University of Southern California Dissertations and Theses

Phytoplankton bloom initiation in the Southern California Bight: a multi-year local and regional analysis

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Phytoplankton bloom initiation in the Southern California Bight: a multi-year local and regional analysis

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Content Phytoplankton
bloom
initiation
in
the
Southern
California
Bight;

A
Multi-‐year
local
and
regional
analysis.

Thesis by
Bridget Noreen Seegers

In Partial Fulfillment of the Requirements for the
Degree of Doctor of Philosophy

University of Southern California
Los Angeles, California

December 2014

i

Table of Contents

Acknowledgements ……………………………………………………………… ii

I. Abstract ………………………………………………………………………. 1
Introduction …………………………………………………………………… 3

II. Chapter 1: Subsurface seeding of surface harmful algal blooms observed through the
integration of autonomous gliders, moored Environmental Sample Processors, and
satellite remote sensing in Southern California ……………………… 15

III. Chapter 2: Pseudo-Nitzschia bloom initiation in the Southern California Bight; Multi-
year local and regional analysis of glider, satellite, and surface current data…….... 51

IX. Chapter 3: Glider and remote sensing perspective of the upper layer response to an
extended shallow coastal diversion of municipal wastewater effluent. ……………. 97

ii

Acknowledgements

The completion of my dissertation required the guidance of my committee
members, the support of lab members, and help from friends and family. It takes a whole
village to raise a graduate student should be a common saying.

Many people have shared their time and thoughtful conversations and comments
with me throughout my graduate school years. I would like to express gratitude to my
advisor, Dr. Burt Jones, for his guidance through the years. He exposed to me to the
exciting research world of optics and autonomous vehicles. He allowed me to take a lead
on many projects as a graduate student giving me the opportunity to work on project
planning and attend primary investigator meetings, which has been an invaluable part of
my graduate education. Dr. Dave Caron was incredibly supportive with his advice and
comments through the years. He helped guide my work to ensure the highest quality and
was available for insightful conversations. Dr. Dale Kiefer is an inspiration in science
and in life. Dr. Doug Hammond was exceptionally supportive with encouraging
conversations and astute comments on my research. Dr. Meredith Howard and Dr. Raphe
Kudela often provided knowledgeable feedback and optimism about my work. Dr. B.
Greg Mitchell inspired this journey with an inspirational conversation on the stern of R/V
Palmer in the Southern Ocean when I was a technician in 2006.

The research I completed required a team to be successful as “autonomous”
robots need quite a bit of attention. Matthew Ragan, Elizabeth Teel, Xiao Liu, Carl Oberg,
Arvind Pereira, Dario Diehl, Alyssa Gellene and Nick Rollins were integral members of
the glider team. In addition to glider operations Nick Rollins assisted with Matlab coding,
insightful conversations, and locating LA’s best surf breaks. Dr. Mattias Cape and Dr.
Randie Bundy are awesome friends that were always willing to give thoughtful reviews
of manuscripts.

The support of my family and friends was immeasurable. Life is about balance
and keeping things in prospective while working hard to accomplish goals. My parents,
Noreen and Jim, and my brothers, Eric, Brian, and Timmy were supportive throughout
the journey. I would like to acknowledge the support of wonderful friends, Elena Perez,
Renee Willette, Seth Azzaline, Jason Vo and the other amazing friends that share the
waves and ocean with me.

1

Abstract
The dissertation research completed was fundamentally an exploration of why, when, and
where do specific types of algal blooms occur with a focus on harmful algal blooms (HABs).
Many bloom events are studied opportunistically or have limited synoptic sampling after the
bloom is established, which leads to an inability to make predictions because bloom initiation
and evolution are seldom observed. The research of blooms often relies on remote sensing and
surface sampling and therefore tends to be 2-D in nature. The problem with this perspective is
that it only sees a fraction of the water column and the euphotic zone, and it has been shown that
subsurface dynamics are important to bloom onset and development especially for localized
events.
I used bio-optical instruments with a focus on multi-month glider deployments combined
with satellite data for in situ and remote sensing monitoring of subsurface and surface ocean
conditions. The gliders provided information about local subsurface ocean biology and physical
dynamics, while satellites give regional large-scale physical and biological data. The gliders
enabled the development of multi-month time series that allowed the study of complex
subsurface ocean dynamics. Gliders can observe physical subsurface features including fronts,
eddies, internal waves, and integrated subsurface current velocities and direction. Additionally,
gliders can lead to better understanding of seasonal variation in phytoplankton blooms related to
a variety of factors including nutrients from upwelling events, rivers, effluent plumes, and
coastal dynamics.
The majority of the research focused on the late winter to spring in the coastal region of
the Southern California Bight. This period was selected, because it historically has the highest
rates of toxic algal blooms dominated by neurotoxin producing Pseudo-Nitzschia genus, which is
a threat to humans and wildlife. Three multi-month field efforts in 2010, 2013 and 2014 were

2

conducted to better understand the initiation and evolution of phytoplankton blooms. Each field
season was successful in monitoring the onset and evolution of a Pseudo-Nitzschia bloom and
revealed a variety of processes associated with bloom initiation. The 2010 revealed for the first
time blooms of toxic Pseudo-nitzschia sp. can develop offshore and subsurface prior to their
manifestation in the surface layer and/or near the coast. The 2013 and 2014 seasons
demonstrated that southward advection and subsequent retention of phytoplankton communities
in the coastal region is at times a primary driver of Pseudo-nitzschia toxic bloom events.
The final chapter combined similar instrumentation to monitor the coastal system during
an extended 3-week wastewater discharge to a near-surface (16 m) near-shore (2 km) outfall.
The combined AUV and remote sensing dataset indicated that in response to the diversion there
was a limited increase in phytoplankton abundance in the upper layer, but that the level of the
response overall was less than expected. A variety of explanation could explain the reduced
phytoplankton response including unexpected high rates of dilution after effluent emission. The
system returned to pre-diversion conditions within 72 hours.
Overall, the research showed that the onset of phytoplankton blooms is the result of a
complex combination of local and regional dynamics. However, the complex nature although it
seems stochastic at times can be understood with extended monitoring and the combination of
advanced instrumentation.

3

Introduction
An introduction to harmful algal blooms (HABs) will give insight into the research
motivation. HABs cause harm by producing toxins or because the accumulated biomass
negatively impacts food-web dynamics and ecosystem structure. HABs can negatively impact
sea-life and human health and additionally hurt economies dependent on healthy oceans
including fisheries, shellfish harvesting, and tourism (e.g., Hoagland, 2002). The negative
impacts of HABs make understanding the physical, chemical, and biological variables
influencing the growth of the phytoplankton community a scientific priority. However, even in
highly studied areas like the California Bight HABs are not easily predicted. Although HABs are
difficult to predict and attempts to forecast bloom events have only been moderately successful,
there is much evidence suggesting that events are not simply stochastic. A clear understanding of
bloom evolution in the region of interest must be temporally and spatially resolved at appropriate
scales before, during, and following the event to recognize the causative processes. Biological
events, such as blooms, often outlast the original conditions that initiated the blooms and can
there for are missed when sampling of a bloom occurs.
HAB diversity
There are hundreds of HAB species and the species differ in the toxins they produce,
which results in a range of deleterious results. The toxins have impacts on wildlife and can cause
human sickness and death. The toxins produce include but are not limited to saxitoxins causing
paralytic fish poisoning (PSP); brevetoxins leading to neurotoxic shellfish poisoning (NSP); and
domoic acid causing amnesic shellfish poisoning (ASP). Dinoflagellates account for about 75%
of toxic HAB species (Smayda, 1997) and produce saxitoxins that causes paralytic fish poisoning

4

(PSP) (Nishitani and Chew, 1988). In addition to producing saxitoxins certain species of
Dinoflagellates are responsible for the “red tide” blooms, which can be toxic or non-toxic.
Dinoflagellate blooms are typically associated with stratified, low nutrient conditions (Shipe et
al., 2008). The Pseudo-nitzschia genus is a pennate diatom with numerous neurotoxin
producing species. Domoic acid (DA) produced by the diatoms Pseudo-nitzschia causes domoic
acid poisoning (DAP) also known as amnesic shellfish poisoning (ASP) (Landsberg, 2002).
ASP negatively impacts a wide range of wildlife from invertebrates to marine mammals and
birds (Wekell et al., 1994, Scholin et al., 2000, Work et al., 1993).

HAB Causes
HABs are difficult to predict and attempts to forecast HAB events have had moderate
success, because of the complexity and uncertainty of the causes. Increase in the reate of HABs
occurrences suggests that anthropogenic causes may be disrupting the phytoplankton
communities. Varying human activities that could be forcing HABs include climate change,
habitat disruption that selects for different algal species, and nutrient loading. Research is
providing insights and information about the consequences of these factors influence on algal
communities, but exactly how these variables independently and collectively influence HABs is
still not fully understood.
HAB events result from the interaction of chemical, physical, and biological ocean dynamics,
which are discussed in details below.

HABs and Nutrients

5

Eutrophication, nutrient loading, of coastal waters is frequently considered an important
cause of HAB events (e.g., Gilbert et al., 2005, 2010, Anderson et al., 2008; Heisler et al., 2008),
although there is still debate about the matter (e.g., Davidson et al., 2012). Large amount of
nutrients are consumed by phytoplankton blooms, and consequently it is reasonable to predict
nutrient loading will lead to blooms. Along the west coast of the USA Trainer et al. (2003)
showed that paralytic shellfish toxins from dinoflagellates over the past 40 years in Puget Sound
have increased with nutrient enrichment of runoff. Howard et al. (2014) calculated that the
steady input of nutrient-rich sewage effluent from ocean outfalls could be an important nutrient
source in the local area with potential to simulate phytoplankton grown if upwelled into the
surface ocean.
Strong upwelling events providing nutrients and therefore some HAB regions are not
traditionally nutrient limited and anthropogenic sources of nutrients would be less likely to be a
driver of bloom formation. California coastal upwelling influences the chemical, physical, and
biological characteristics of the water. The nutrient flux to the upper ocean through upwelling is
generally much greater than anthropogenic sources (Hood et al., 1992; Anderson et al., 2008),
although in specific regions anthropogenic inputs could be on the same order of magnitude
(Howard et al., 2014). Currently, no direct linkages have been made between Pseudo-nitzschia
blooms and run-off events along the southern California coast (Anderson et al., 2008, Schnetzer
et al., 2013). The results linking Pseudo-nitzschia blooms to nutrient sources near Los Angeles
have had contradicting results. Schnetzer et al. (2007) found a negative correlation between
Pseudo-nitzschia abundance and nitrogen, silicon, and phosphate concentration, however the
study was completed after the bloom was established and the nutrients could have been drawn
down from higher phytoplankton concentrations of the bloom. Shipe et al. (2008) found a

6

positive correlation of Pseudo-nitzschia cell concentrations with nitrate, dissolved silicon, and
phosphate early in blooms, but as blooms persisted, nutrients were drawn down and the
correlation was lost. Moreover, the same study found Lingulodidinium polyedrum and
Prorocentrum micans, dinoflagellate species, bloom soccurred during highly stratified, low
nutrient conditions, indicating different nutrient conditions support different HAB species. In
other coastal upwelling regions along the coast nutrient types and input into the system was
found to be important. Kudela et al. (2008) focused on urea concentration in California waters
during past HABs and found that the blooms were sustained by urea that most likely was from
anthropogenic sources. A L. polyedrum red tide bloom in Southern California acquired 38% of
its nitrogen demand from urea, despite low levels of urea relative to ammonium concentrations
(Kudela and Cochlan, 2000). More recently much research has focused on the influence
increased CO
2
may have on HABs with a variety of results including increased growth rates (e.g.,
review Fu et al., 2012). Increased toxin production was measured with increased CO
2
in the
toxic diatom Pseudo-nitzschia sp. (Sun et al., 2011, Tatters et al., 2012). The research
demonstrates that although HABs are naturally occurring HABs are sensitive to a range of
anthropogenic changes in the environment.

Physical Forcing
Nutrients alone are unable to explain the occurrence of HABs and physical environmental
characteristics are another potential HAB driver. Smayda and Reynolds (2001) used an
ecological model to demonstrate that mixing and nutrient conditions have the ability to select for
specific algal groups including HAB species. In the Santa Monica Bay a multivariate analysis by
Shipe et al. (2008) found that temperature and mixed layer depth, in addition to nutrient

7

concentrations, were the primary controls on phytoplankton primary production in HAB species
Pseudo-nitzschia, P. micans, and L. polyedrum. Additionally, in Monterey Bay, California a
predictive model by Lane et al. (2009) found that silicon concentration combined with seasonally
specific temperature, upwelling index, and nitrate concentration provided the strongest predictive
power of Pseudo-nitzschia blooms. These results indicate that nutrients combined with physical
features are significant in HAB formation.
Glider surveillance in the California current off of Southern California has shown that
fronts in seawater properties including seawater density relate to fronts in phytoplankton
communities and that the physical fronts can lead to abrupt biological changes, which sometimes
includes blooms (Davis et al., 2008). Eddies can result in nutrient upwelling and the retention of
phytoplankton within the eddy (Macfadyen et al., 2008, Todd et al., 2009). Macfadyen et al.
(2008) focused on the Juan De Fuca Eddy in the northern section of the California Current and
found that when eddy surface circulation is more retentive HABs are more likely to occur.
Another source for HAB initiation is the subsurface population of HAB species. The
subsurface phytoplankton populations seeding surface blooms had been unobserved until this
dissertation research was completed in the Southern California Bight (Seegers et al. submitted).
Numerous studies have shown that HAB species cells can travel long distances and that offshore
HABs can be the source for the near shore HABs (Trainer et al, 2000, 2002, 2009, Macfadyen et
al., 2008). Upwelling systems are highly productive areas and much focus has been given to
upwelled nutrients influences on primary production generally (e.g. Eppley et al., 1979,
Wilkerson and Dugdale, 1987) and on HABs in particular (e.g. Kudela et al., 2005, 2010, Pitcher
et al., 2010). Although long theorized as potentially important the actual seeding of surface
blooms by the subsurface phytoplankton population during upwelling events has received

8

considerable less attention (Jones and Brink, 1985). Thorough reviews of Pseudo-nitzschia and a
variety of parameters affecting Pseudo-nitzschia blooms, growth, and toxicity by Lelong et al.
(2012), Anderson et al. (2012), Trainer et al. (2012) mention the importance of upwelling
nutrient fueling blooms, but only briefly or do not mention that subsurface populations may seed
surface blooms.
More recently the importance of “thin layers” as a source for surface HAB events has
been used to explain the sudden appearance of HAB species and events (Trainer et al., 2000,
McManus 2008). Focusing on Monterey Bay McManus et al. (2008) completed high resolution
vertical surveying and discovered a subsurface thin layer dominated by HAB species between 10
centimeters and 3 meters thick. In Santa Monica Bay, California during early bloom conditions
Pseudo-nitzschia dominated all depths except the surface five meters, however, 2 weeks later in
established HAB conditions Pseudo-nitzschia dominated all depths with a maximum
concentration at 20 meters, which suggests that subsurface population could be a source (Shipe
et al., 2008). Unfortunately, most of the subsurface distributions are often missed by standard
monitoring methods.

Biological Forcing of HABs
Chemical and physical variables have been addressed to explain HABs, but biological aspects,
especially the impacts of grazing, must be explored to gain a full understanding of HAB
establishments. Top down control of phytoplankton populations by grazing zooplankton can
have a significant impact on primary producer biomass (eg., Calbet and Landry, 2004; Strom et
al., 2007; Chen et al., 2009). Calbet and Landry (2004) completed an extensive review of nearly
800 oceanic autotropic growth and microzooplankton grazing experiments and found that overall

9

67% of growth is lost to grazing. Many HAB species produce toxins that deter zooplankton
grazing, which could provide these species with an opportunity to bloom (Flynn, 2008). Goleski
et al. (2010) demonstrated a lack of grazing pressure enabled the establishment of the HAB
caused by cyanobacteria. Smayda (2008) focused on grazing pressure and HABs in Chesapeake
Bay and found that the bloom initially established after a collapse in grazing pressure and the
eventual restoration of grazing pressure reduced the bloom and deomonstrated that grazers are
important to regulating HABs (Smayda, 2008). Unfortunately, HAB studies often do not include
grazing rates and therefore much remains unknown about HABs and the impacts of grazers.

Conclusion
Harmful algal blooms have been increasing globally with negative consequences for wildlife and
human health and detrimental economic impacts, which led to HABs becoming a recent research
priority. Previous research has shown that chemical, physical, and biological factors are
influencing HABs. The dissertation research presented here is unique bringing together a range
of new instrument technology. The fundamental tool in the work is are gliders (autonomous
underwater vehicles) capable of multi-month in-situ sampling of the region and this data set was
combined with supplementary data sets resulting in new insight into the onset and evolution of
HABs in the Southern California Bight.

10

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McLaughlin K., Sengupta, A. (2014). Anthropogenic nutrient sources rival natural
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Lane JQ, Raimondi PT & Kudela RM. (2009). Development of a logistic regression model for
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13

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Sample Processors, and satellite remote sensing in Southern California. Limnology and
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phytoplankton blooms in the sea. Limnology and Oceanography 42, 1137-1153.
Smayda TJ. (2008). Complexity in the eutrophication-harmful algal bloom relationship, with
comment on the importance of grazing. Harmful Algae 8, 140-151.
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Sun J, Hutchins DA, Feng Y, Seubert EL, Caron DA, Fu FX. (2011). Effects of changing pCO2
and phosphate availability on domoic acid production and physiology of the marine
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Tatters AO, Fu FX, Hutchins DA (2012). A CO
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of the harmful bloom diatom Pseudo-nitzschia fraudulenta. PLoS ONE 7: e32116.
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Paralytic shellfish toxins in Puget Sound, Washington State. Journal of Shellfish
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15

Chapter 1: Subsurface
seeding
of
surface
harmful
algal
blooms
observed
through
the

integration
of
autonomous
gliders,
moored
Environmental
Sample
Processors,
and

satellite
remote
sensing
in
Southern
California.

Originally submitted to Limnology and Oceanography July 10, 2014.
Accepted December 15, 2014

Bridget
N.
Seegers
1
,
James M. Birch
2
, Roman Marin III
2
, Chris
A.
Scholin
2
,
David
A.
Caron
1
,

Erica
L.
Seubert
1
,
Meredith
D.
A.
Howard
3
,
George
L.
Robertson
4
,
and
Burton
H.
Jones
1,
5

1
Department of Biological Sciences, University of Southern California, 3616
Trousdale

Parkway,
Los Angeles, California 90089-0371, USA
2
Monterey Bay Aquarium Research Institute (MBARI), 7700
Sandholdt
Rd,
Moss
Landing,

California
95039, USA
3

Southern
California
Coastal
Water
Research
Project,
3535
Harbor
Blvd
#110,
Costa
Mesa,

California
92626, USA
4
Orange Country Sanitation District, 10844
Ellis
Ave,
Fountain
Valley,
California
92708,
USA
5
King Abdullah University of Science and Technology, 4700 KAUST, 23955-6900, Thuwal,
Kingdom of Saudi Arabia

16

Acknowledgements
We thank the USC glider team for their support, especially M. Ragan, C. Oberg, B.
Stauffer, G. Toro-Farmer, I. Cetinic, E. Teel, and X. Liu. Doug Hammond provided
insightful discussions. Captain Ray Arntz and Sundiver crew ably provided support for
glider deployments and recovery. Captain Jim Christman of the R/V Shana Rae, Scott
Jensen, and volunteer divers from the Long Beach Aquarium of the Pacific assisted in the
ESP deployment and recovery.
The research was supported by NOAA ECOHAB grant NA11NOS4780052, California
Sea Grant, NOAA Monitoring and Event Response for HABs (NA05NO54781228),
California Ocean Protection Council (Grant Agreement 08-095), the State Water
Resources Control Board (Agreement 08-060-250), and USC Sea Grant.

17

Abstract

An observational study was performed in the central Southern California Bight in
Spring 2010 to understand the relationship between seasonal spring phytoplankton
blooms and coastal processes that included nutrient input from upwelling, wastewater
effluent plumes, and other processes. Multi-month Webb Slocum glider deployments
combined with MBARI environmental sample processors (ESPs), weekly pier sampling,
and ocean color data provided a multidimensional characterization of the development
and evolution of harmful algal blooms (HABs). Results from the glider and ESP
observations demonstrated that blooms of toxic Pseudo-nitzschia sp. can develop
offshore and subsurface prior to their manifestation in the surface layer and/or near the
coast. A significant outbreak and surface manifestation of the blooms coincided with
periods of upwelling, or other processes that caused shallowing of the pycnocline and
subsurface chlorophyll maximum. Our results indicate that subsurface populations can
be an important mechanism “seeding” surface Pseudo-nitzschia HAB events in Southern
California.

Keywords: phytoplankton; harmful algal blooms; subsurface chlorophyll maximum;
coastal upwelling;

18

Coastal continental shelf regions are areas of high ocean primary production and
efficient energy transfer to higher trophic levels, contributing to their ecological and
economical value. These shelf regions are also vulnerable to harmful algal blooms
(HABs), which are defined as significant increases in phytoplankton biomass with
harmful consequences such as toxin production or the accumulation of biomass that
negatively impacts food-web dynamics and ecosystem structure. Globally the occurrence
of HABs has been increasing for decades accompanied by longer bloom duration and
increased toxicity (e.g., Hallegraeff, 1993). The diatom Pseudo-nitzschia, a predominant
HAB genus of concern, produces the neurotoxin domoic acid (DA) that threatens the
health of humans and wildlife from invertebrates to marine mammals and birds. Further
details on Pseudo-nitzschia, including its physiology, toxicity, and global impacts of
toxic events, have been thoroughly summarized in reviews by Anderson et al. (2012),
Lelong et al. (2012), and Trainer et al. (2012).
The negative ecological and economic impacts of HABs have resulted in a desire
for increased understanding of the physical, chemical, and biological variables
influencing their success in natural phytoplankton communities. Many HAB events are
studied opportunistically or have limited synoptic sampling, resulting in an inability to
resolve the bloom initiation and subsequent evolution. In addition, HAB research often
relies on remote sensing and surface sampling and therefore limits observations to the
near-surface region. A fundamental drawback of this approach is that it visualizes only a
fraction of the water column and the euphotic zone. In the Southern California Bight
much focus has been given to the upwelling nutrient dynamics influence on HABs
(Kudela et al. 2005, 2010, Pitcher et al. 2010). A variety of predictive models that

19

typically rely on nutrient concentrations and ratios, temperature, mixed layer depth, and
stratification strength have been developed to better understand the conditions under
which Pseudo-nitzschia blooms develop, but these models have had limited predictive
power (e.g., Lane et al., 2009, Anderson et al., 2011). The models often focus on the
availability of upwelled nutrients in surface waters to support growth and accumulation
of the surface phytoplankton community into blooms. The models tend to overlook
subsurface phytoplankton communities that are upwelled along with the nutrients into the
surface layer and affect surface plankton community composition and bloom initiation.
Unfortunately, much of the subsurface structure and dynamics are often missed by
standard monitoring methods.
The advection of HAB species from one location to another and from subsurface
to surface has initiated blooms in the new location. Studies have shown that HABs can be
entrained into surface water masses that can advect cells great distances both along shore
and cross-shelf. Trainer et al. (2002) and Macfadyen et al. (2008) documented this
transport of Pseudo-nitzschia and its impact on coastal waters along the Washington
coast. More recently the importance of subsurface thin layers as a source for surface
HAB events was hypothesized as an explanation for the sudden appearance of HAB
species and events (Trainer et al., 2000, McManus, 2008). Tilestone et al. (2000) showed
that Iberian upwelling could transport diatoms on the shelf and Crespo et al. (2007)
suggested that surface currents could then transport the diatoms. Field observations have
shown the potential importance of upwelling transport of subsurface dinoflagellate
populations to initiate and maintain surface blooms (e.g., Tyler and Seliger 1978, Pitcher
et al., 1998, 2010). Modeling results have also shown wind-driven subsurface Ekman

20

flow could move subsurface phytoplankton population into surface layers initiating
blooms (Janowitz and Kamykowski, 2006), yet these types of movements and initiation
events have been unobserved for diatoms.
The goal of this effort was to better understand the onset and connections between
subsurface and surface blooms of the toxic diatom, Pseudo-nitzschia off the southern
California coast. Toxic blooms of Pseudo-nitzschia are a recurring problem in this area
with some the highest DA concentrations per cell reported for natural populations
(Schnetzer et al., 2007; 2013). San Pedro Bay, in the central Southern California Bight, is
strongly influenced by both anthropogenic urban inputs and coastal upwelling, both of
which can contribute to phytoplankton blooms and HAB events. Major sources of
anthropogenic nutrients in this region include two ocean outfall diffusers operated by the
Orange County Sanitation District (OCSD) and the Los Angeles County Sanitation
District (LACSD) and three channelized riverine sources (Los Angeles River, San
Gabriel River, Santa Ana River). Wastewater effluent from the subsurface outfalls
contains concentrations of nitrogen and phosphorus that are up to three orders of
magnitude greater than maximal ambient nutrient concentrations, and the buoyant
effluent plumes also entrain deeper, nutrient enriched, sub-nutricline water as they rise to
their equilibrium depth. These nutrient fluxes contribute significantly to total nutrient
budgets in this coastal region (Howard et al., 2014), and therefore may contribute to the
growth of subsurface populations of Pseudo-nitzschia.
This project combined multi-month glider deployments, mooring and pier
phytoplankton community composition and temperature data, and remotely sensed
satellite ocean color and temperature data, which allowed for the monitoring of

21

conditions associated with the evolution of a Pseudo-nitzschia bloom from onset to
demise. The moored ESPs confirmed an offshore subsurface population of Pseudo-
nitzschia and the glider data showed that upwelling moved the subsurface plankton
communities into the surface waters, which resulted in a Pseudo-nitzschia bloom and
demonstrated for the first time that upwelled subsurface phytoplankton populations can
initiate HABs in the region.
Methods
The study was conducted in the central Southern California Bight (SCB) with a
focus on the San Pedro Channel, near the Los Angeles Harbor (Figure 1). The San Pedro
Channel provides us with a unique environment to study the seasonal variation in
phytoplankton blooms related to a variety of processes including nutrient inputs from
coastal upwelling, river runoff, and treated sewage effluent plumes, and other coastal
processes.
Equipment and Sampling
Webb Slocum Glider
A major goal of the research was to observe the coastal ocean before, during, and
after HAB events with a particular focus on signs of HAB population advection into the
surface water from the subsurface. Webb Slocum G1 shallow-water gliders were
employed to provide spatial mapping of key variables over an extended period of time,
and data transferred from the gliders were used in the decisional process for triggering
opportunistic sampling (e.g. ship sampling). A glider was deployed continuously during
the spring of 2010 from late February through mid-June, a time window when upwelling
tends to be most intense in the region. The glider ran a zigzag pattern in the San Pedro

22

Bay on and off the shelf (Figure 1). The glider dove in a sawtooth pattern 3 m from the
surface to 4 m from the bottom on the shelf or to a depth of 100 m off the shelf. The
glider was equipped with a Sea-Bird conductivity-temperature-depth sensor (SBE-41cp
CTD), a GPS, Iridium communications enabling daily data transmission, and WET labs
ECO pucks optical instruments. The optical sensors included three fluorometers with
excitation/emission channels that measured chlorophyll a (470nm/695nm), colored
dissolved organic matter (CDOM) (370nm/460nm) and phycoerythrin/ rhodamine
(540nm/570nm), and an optical backscatter sensor at 3 wavelengths.
The glider recoveries occurred approximately every 3 weeks throughout the
deployment period and were based from the University of Southern California’s Wrigley
Institute for Environmental Studies on Catalina Island, where cleaning, calibrations and
battery change could occur quickly, thereby minimizing data gaps. The frequent
recovery and maintenance helped to reduce biofouling on the sensors. The glider
chlorophyll fluorometer was calibrated pre- and post-deployment using a serial dilution
of a local mixture of cultured phytoplankton species (Cetinić et al., 2009). These
measurements allowed us to monitor for long-term stability of the sensors and for effects
of biofouling. A mix culture calibration does not ensure a representative chlorophyll
concentration for all in situ phytoplankton communities encountered, but was
implemented to help reduce any biases. Glider chlorophyll concentrations often show a
diel cycle mainly in the surface 4 to 20 m (Davis et al., 2008), which is largely attributed
to nonphotochemical quenching (Kiefer, 1973). No corrections were made for quenching,
because we were more interested in temporal and spatial patterns than the exact

23

chlorophyll concentration and the values reported should only be considered very
approximate values.
The glider did not have nutrient sensors, but nutrients and temperature are well
correlated in the SCB and the nutricline in the Southern California region has long been
associated approximately with the 13°C isotherm (Armstrong and LaFond 1966).
Therefore, we used temperature to roughly estimate the depth of the nutricline in the
water column. Additionally, the temperature proxy can be used as an indicator for the
appearance of nutrient-rich upwelled waters shoaling into the surface layer. Regional and
seasonal specific temperature to nutrient relationships have been developed using the
nutrient data set from CalCOFI’s (California Cooperative Oceanic Fisheries
Investigations) southern California seasonal transects (Todd et al, 2009, Lucas et al.
2011). We used the CalCOFI 2010 winter and spring cruise data from the San Pedro Bay
study region to develop a 2010 specific nutrient and temperature relationship for the
glider deployments. Temperature was used as opposed to density as a nutrient proxy,
because some of the analyzed data sets had only temperature available.
Barnacle Domoic Acid
Gooseneck barnacles (order Pedunculata) often covered the glider following 3 or
more weeks of deployment. These barnacles were collected and stored in Falcon
®
tubes
at -20°C until analyzed for domoic acid by enzyme-linked immunosorbent assay (ELISA)
by Mercury Science (Durham, NC). A minimum of 1g of whole barnacles were
sonicated in 3mL of 10% methanol until the body tissues were liquefied, typically
between 30 and 60s. Samples were centrifuged for 10 minutes at 4000rpm, the
supernatant was diluted with the sample dilution buffer provided by the manufacturer and

24

the resulting detection limit was 0.005µg domoic acid/g body weight. The accuracy of
the ELISA for DA analysis in shellfish tissues has been validated and the assay gives
results equivalent to those acquired by standard high performance liquid chromatography
(Litaker et al., 2008).
Environmental Sample Processors (ESPs)
Two Environmental Sample Processors (ESPs) were deployed at fixed points in
the San Pedro Channel from 2 to 28 April for in situ measurements of potentially toxic
algal species, and concentrations of particulate domoic acid (Figure 1). The ESP is an
electro-mechanical device that filters seawater and either archives the filtrate for later
analysis, or performs a variety of analytical tests on board the instrument. For this
deployment, the instruments were configured to detect several species of Pseudo-
nitzschia and other HAB targets groups using DNA probes targeted to sequences in the
large subunit of the ribosomal gene (Scholin 1997, Greenfield et al. 2006). The probes
work via a sandwich hybridization array (SHA), resulting in spots of varying intensity
depending on target concentration. The presence and relative abundances of HAB species
were estimated from the intensity of probe spots on a filter membrane relative to filter
background as measured by a CCD camera (Greenfield et al. 2008). In this deployment
we were unable to create standard curves that would assign cell abundances to spot
intensity and thus, report only trends in diatom abundances and domoic acid
concentrations that the ESP measured. The ESP’s were moored near the glider transect
off of Huntington Beach suspended at an average depth of ~17 meters in an attempt to
sample the subsurface chlorophyll maximum. One ESP (“ESPnearshore”) was moored 4
km from shore at the 30m isobaths (33° 36.373'N, 118° 1.284'W). The second ESP

25

(“ESPoffshore”) was placed 7km from shore at the 60m isobath (33° 35.125'N, 118°
2.248'W ) (Figure 1).
MODIS
Level 3 Aqua MODIS sea surface temperature (SST) and chlorophyll-a
concentration (chl-a) data with 0.0125 degree pixel resolution obtained from the West
Coast Regional Node of National Oceanic and Atmospheric Administration (NOAA)
CoastWatch were analyzed throughout the glider deployment to monitor for surface
manifestations of algal blooms. Linking these data from near-surface measurements
(provided by satellite imagery) and subsurface measurements (provided by gliders)
provided a 3-dimensional perspective of bloom development, propagation and density.
Newport Pier Surface Data
The data collected during this project was enriched with data from the Southern
California Coastal Ocean Observing System (SCCOOS). SCCOOS provides a weekly
service of HAB species sampling from six piers including Newport Pier in our sampling
area. The weekly Pseudo-nitzschia counts are separated into Pseudo-nitzschia
delicatissima and seriata groups and we report the total Pseudo-nitzschia abundance.
This ongoing pier monitoring (www.sccoos.org) encompassed several variables
including HAB species, discrete surface chlorophyll concentration, discrete surface
particulate DA (pDA) with a limit of detection of 0.1 µg l
-1
and continuous temperature.
Upwelling Index
Conditions conducive to coastal upwelling in the region were monitored using the
Pacific Fisheries Environmental Laboratory (PFEL)
upwelling index (UI) calculated from
the intensity of upwelling-favorable wind for the southern California location at 33 °N,

26

119 °W, approximately 100 km offshore to the southwest from the study area, and data
were obtained from PFEL website (http://www.pfeg.noaa.gov/).

The offshore water
transport estimates (m
-3
s
-1
per 100m of coastline) were calculated every six hours and
daily averaged UI were available.
Results

The CalCOFI 2010 winter and spring nutrient data overlapped with the glider
deployment revealing that there was a steady increase in nitrate and phosphate
concentrations with decreasing temperature starting at 13.5 °C (Figure 2). The 2010
seasonal-specific information was used to confirm the appropriateness of the 13.5°C
isotherm to estimate the nutricline depth and to roughly approximate the initial
appearance of shoaling nutrient-rich waters into the surface layer.
Compared with other reported observations from the region (Schnetzer et al. 2007,
2013) the 2010 spring deployment season was a relatively uneventful HAB year in the
SCB (Seubert et al, 2013). However, a large Pseudo-nitzschia bloom followed a pair of
2-day upwelling events that occurred 5 days apart in late April. The first upwelling
episode occurred on 20 and 21 April, when the daily UI rose above 300 m
-3
s
-1
per 100 m
of coastline. A 5-day lull in the winds from 22 to 27 April followed, when the UI dropped
to 2 m
-3
s
-1
per 100 m of coastline before upwelling favorable winds returned on 28 April,
when the UI again rose to more than 300 m
-3
s
-1
per 100m of coastline. Surface
temperatures at Newport Pier responded to the upwelling favorable conditions with a
corresponding decrease from near 18˚C on 17 April to below 13˚C on 22 April followed
by a brief warming after which temperatures again decreased below 13˚C on 30 April
(Figure 3). Surface chlorophyll concentrations at the Newport Beach Pier increased from

27

1 µg l
-1
on 12 April to 11.4 µg l
-1
on 26 April (not shown), and the total Pseudo-nitzschia
abundance increased from undetected prior to the wind event to 1.30
x
10
4

cells l
-1
on 26
April and increased to nearly 2.80 x
10
4

cells l
-1
a week later on 3 May (Figure 3).
The two ESPs detected cooling of the surface waters due to the 20 April
upwelling event along with an increase in P.multiseries/pseudodelicatissima probe signal
(Figure 3). At the onset of upwelling, the ESPs were moored just above the subsurface
chlorophyll maximum based on glider and boat observations. Although suspended at the
same depth and moored only 3km apart, the two ESPs experienced the upwelling
response at distinctly different times, as indicated by the temporal patterns of temperature
and Pseudo-nitzschia counts. ESPnearshore, 4km from shore, experienced a sharp
decrease in temperature from 15.5°C to less than 12°C on 20 April and began to warm on
23 April

as the upwelling relaxed (Figure 3). Pseudo-nitzschia was not observed at
ESPnearshore until after the upwelling on 25 April and the population showed a steady
increase until the ESPs were removed on 28 April. ESPoffshore experienced a shorter
period of cooling and the temperature dipped below 12°C only for only a single day on
21 April (Figure 3). The appearance of P.multiseries/pseudodelicatissima coincided with
the initial cooling at ESPoffshore on 21 April and steadily increased until the ESP
stopped sampling on 24 April

(Figure 3).
The glider was removed 19 to 23 April for calibrations and therefore glider data
begins on 23 April and captures the second late-April upwelling event (Figure 4). The
glider observations show upward tilting of isotherms (Figure 4A) and chlorophyll
isopleths (Figure 4B) toward the coast and into the surface waters revealing connectivity
between the subsurface and surface communities. The 13.5°C isotherm indicating the

28

estimated temperature intercept for the top of the nutricline reached the surface
accompanied by elevated chlorophyll and the elevated chlorophyll was sustained in the
surface layer (Figure 4D). The upwelling event marked by the tipping isotherms was
short lived and gliders observed subsequent shoreward advection of the 13.5°C isotherm
and sinking of the nearshore chlorophyll maximum on 3 May, which led to the
reestablishment of a subsurface chlorophyll maximum where the subsurface chlorophyll
concentration was higher after the upwelling event than prior to the event (Figure 4 E, D).
The glider data revealed significant temporal and spatial complexity including the
occurrence of internal waves affecting cross-shelf patterns (not shown). The glider
observations demonstrated continuity between the subsurface and surface layers during
the upwelling event and subsequent relaxation (Figure 4).
The three glider deployments provided sufficient barnacle biomass from the glider
exterior for measurements of DA in the barnacle tissue. The barnacle tissue always
tested positive for DA ranging from 0.32
µg g
-1
to 1.75 µg g
-1
(Table 1). The harvested
glider barnacles tested positive for domoic acid even when the weekly near shore pier
surface samples detected no domoic acid or Pseudo-nitzschia.

MODIS SST and chlorophyll images show regional change associated with the
late April upwelling event. On 19 April SST in the San Pedro Channel ranged from 16 to
17°C (Figure 5A) and elevated chlorophyll concentrations ranging from 2 to10 µg l
-1

were found within 2 km of the coast (Figure 5B). On 24 April the regional SST had
cooled 1 to 3°C with the most dramatic cooling nearshore where temperatures had
dropped to 13.5°C due to upwelling (Figure 5C). MODIS chlorophyll imagery provides
an effective view of the spatial extent of surface phytoplankton concentrations.

29

Chlorophyll concentrations on 24 April were greater than 10 µg l
-1
throughout the
nearshore region (Figure 5D). Both the glider chlorophyll fluorescence and satellite
chlorophyll show elevated surface chlorophyll concentrations close to the coast. The
combined images demonstrate continuity between the high chlorophyll region at the
surface close to the coast and deepening into the subsurface chlorophyll maximum away
from the coast. The combined glider and MODIS chlorophyll pattern verified that the
high nearshore MODIS chlorophyll was not an artifact resulting from either elevated
suspended particle concentrations, that characterize Case 2 waters, or land effects (Figure
5E).
Discussion

The development, establishment, and dissipation of a HAB event were observed
through a combination of glider observations, pier sampling, ESPs, and satellite ocean
color imagery. The continuity between the subsurface phytoplankton community and the
surface community during an upwelling event suggests that upwelling both transported
nutrient-rich waters and seeded HAB populations into the surface waters, resulting in an
intensified and sustained bloom event.
A bloom resulting from a nutrient rich upwelling event is not surprising, but the
demonstrated subsurface phytoplankton population seeding of a surface bloom was new.
Seasonal upwelling brings deep nutrient-rich waters to the surface waters providing
nutrients to support blooms. Nutrients must be available to support high levels of
primary production that support HABs, but nutrients alone do not tell the story. Our
results revealed a direct connection between subsurface and surface populations at the
time of the appearance of the surface bloom, indicating that subsurface populations could

30

influence surface community composition by seeding the surface outbreaks. The
existence of a subsurface offshore Pseudo-nitzschia population was confirmed by the
ESP results and the connection of the subsurface phytoplankton populations to the
surface was shown by the glider observations.
The initiation of the observed surface bloom event through advection is further
supported, because the rate of population increase of Pseudo-nitzschia was much greater
than could be explained solely by cell division. If the bloom was simply a growth rate
response to the influx of nutrient-rich upwelled waters on 23 April, then a growth rate of
about 1.8 day
-1
, which exceeds maximum observed growth rates in the region, would be
necessary to increase the Pseudo-nitzschia surface population in 4 days from below the
detection limit of 2,600 cells l
-1
to the observed 1.4 X 10
5
cells l
-1
for Pseudo-nitzschia
seriata and delicatissima classes combined on 26 April. The species P. multiseries and P.
australis, common along the California coast, have reported growth rates for cultures of
0.3-0.9 day
-1
depending on species, strain, light intensity, and nitrogen source (Hillebrand
and Sommer, 1996, Howard et al., 2007, Auro and Cochlan, 2013). Reported growth
rates of natural populations during short incubations are from 0.88 to 1.19 day
-1
(Howard
et al., 2007). Therefore, growth rate alone is unlikely to account for the quick increase in
Pseudo-nitzschia population.
Domoic acid results from the barnacles support the persistence of a subsurface
population of toxic Pseudo-nitzschia. Tissue samples from barnacles that grew on the
gliders during deployments contained low levels of domoic acid, indicative of the
presence of the Pseudo-nitzschia throughout much of the year in the area where the glider
was deployed. The barnacles harvested from the glider contained domoic acid even when

31

the weekly near shore pier surface samples detect no domoic acid or Pseudo-nitzschia.
Although the ELISA results do not identify exactly when and where the domoic acid was
encountered, positive results confirmed that during the glider deployment the barnacles
encountered domoic acid-laden Pseudo-nitzschia.
Subsurface seeding populations influencing surface blooms has long been
theorized as an important mechanism (Wilkerson and Dugdale 1987), but research efforts
have not focused on the subsurface seeding mechanism for initiating Pseudo-nitzschia
events. Thorough reviews of Pseudo-nitzschia and a variety of parameters affecting
Pseudo-nitzschia blooms, growth, and toxicity by Lelong et al. (2012), Anderson et al.
(2012), Trainer et al. (2012) have noted the importance of upwelled nutrients fueling
blooms, but the role of subsurface populations in seeding surface blooms was rarely
addressed. Yet, the evidence supporting the presence of subsurface seeding populations
is increasing. Pseudo-Nitzschia dominated subsurface chlorophyll maximums (Ryan et
al., 2005, Shipe et al., 2008) and thin layers have been observed along the California
coast (e.g., Rines et al. 2002, McManus et al., 2008). In Santa Monica Bay, California
prior to a surface bloom, Pseudo-nitzschia dominated all depths except the surface 5
meters. However, 2 weeks later Pseudo-nitzschia dominated all depths with a maximum
concentration at 20 meters, that indicated the subsurface population could be particularly
important (Shipe et al., 2008). Thin layers have been implicated as an explanation for the
sudden appearance of a large HAB event as well as “cryptic blooms”, toxicity without
large increases in surface phytoplankton (Rines et al., 2002, McManus et al., 2008).
The cross-shelf subsurface transport of phytoplankton along shoaling isopycnals
was demonstrated by the combined glider and ESP observations and has been shown in

32

other studies to occur coastally in the SCB. Noble et al. (2009) completed a study in the
San Pedro Channel showing cross-shelf transport of subthermocline water and dissolved
and particulate materials including phytoplankton associated with shoaling internal tides.
Lucas et al. (2011) in the SCB demonstrated potential effects of subsurface isopycnal tilt
and thermal stratification on surface phytoplankton productivity, biomass, and
community composition. Likewise, the offshore ESP detected a subsurface population of
Pseudo-nitzschia that steadily increased in abundance along shoaling isopycnals prior to
mixing with the nutrient-rich deep waters, suggesting that shoaling may relieve light
limitation, possibly promoting increased subsurface phytoplankton growth.
An important role for the seeding of surface blooms by subsurface algal
populations might also provide an explanation why nutrient rich surface run-off events
have not been strongly linked to Pseudo-nitzschia blooms along the southern California
coast (Anderson et al., 2009; Schnetzer et al., 2013). Surface nutrients augmented by a
storm event may support algae already present in surface waters, but would not trigger a
Pseudo-nitzschia bloom if the population is located in deeper waters not directly coupled
to the surface.
Anthropogenic inputs in the region could remain an important HAB variable
although anthropogenic nutrient enrichment may not have directly initiated this Pseudo-
nitzschia HAB events. Howard et al (2014) showed that wastewater effluent could make
a significant contribution to the total nitrogen in the San Pedro region and potentially
these effluent derived nutrients could contribute to primary production when upwelled to
surface waters. Anthropogenically influenced nutrient regimes can affect Pseudo-
nitzschia HAB events in a variety of ways including shifting nutrient ratios and forms

33

(e.g. nitrate, ammonia, or urea), that may sustain an event, shift the community species
composition, or increase the toxicity of the cells (e.g. Kudela et al., 2008, Loureiro et al.,
2009). Howard et al. (2007) have shown that some natural assemblages of Pseudo-
nitzschia can double their domoic acid content when utilizing urea, an indicator of
eutrophication, as a nitrogen source as opposed to either nitrate or ammonium.
Furthermore, anthropogenic nutrient enrichment modifies the nutrient ratios within an
environment, and domoic acid production is sensitive to shifting macronutrient ratios
(Anderson et al., 2006).
The contribution of a seed population to nearshore surface blooms suggests that
bloom development depends on an upwelling event, but does not ensure that every
upwelling event will lead to a bloom of Pseudo-nitzschia. A variety of factors can
influence bloom establishment such as upwelling duration, intensity, frequency,
subsurface population structure, and subsequent stratification of the water column.
Upwelling duration will influence the nutrient concentrations and ratios injected into the
surface waters. If the upwelling is too intense or persistent the subsurface populations
could be pushed offshore resulting in no nearshore surface bloom. In the Santa Barbara
Channel Anderson et al. (2011) observed a decoupling of nearshore and offshore HAB
events, which may be explained by prolonged upwelling-driven offshore transport of the
phytoplankton. A combination of upwelling and relaxation events has been shown to be
important in bloom establishment and the Pseudo-nitzschia bloom observed in this study
resulted after an upwelling-relaxation-upwelling cycle comprised of a pair of 2-day
upwelling events separated by a 5-day relaxation period. Wilkerson et al. (2006)
demonstrated the importance of upwelling duration and relaxation along the California

34

coast and found an optimal 3-7 day window of relaxed winds after an upwelling event to
allow for chlorophyll accumulation. Velo-Suárez et al. (2010) showed the combination
upwelling and relaxing events can also be important to the formation and maintenance of
thin layers that may serve as incubator for HABs. Therefore, a consideration of the
duration of upwelling and the timing of a series of upwelling/relaxation sequences along
with water column physical structure such as persistent stability could improve model
success in predicting Pseudo-nitzschia bloom establishment and dynamics.
MODIS satellite remote sensing observations enabled the extrapolation of the
glider observations to regions beyond the operational region of the gliders by providing
synoptic snapshots of the near-surface ocean on larger space and longer temporal scales
(Figure 5). Satellites have been used to monitor the extent of HABs and satellite analysis
is becoming an increasing popular method for detecting blooms along the California
coast (Anderson, et al. 2009, 2011, Nezlin et al. 2012). Satellite ocean color imagery
provides an estimate of ocean near surface chlorophyll, which can indicate bloom
occurrence. Combining glider data with satellite imagery provides a more complete
resolution of the temporal and spatial history of HAB initiation and establishment. The
offshore extent of the surface chlorophyll seen by the glider aligns well with the offshore
extent observed by satellite imagery. Gliders are an effective way to expand the surface
satellite imagery to observe subsurface phytoplankton populations and their variability.
In situ subsurface measurements remain essential to fully understand the development
and evolution of phytoplankton populations.
The combined approach of using multi-month in situ monitoring and high
resolution remote sensing of Southern California Bight coastal blooms provided unique

35

insight into the subsurface phytoplankton population seeding of a coastal surface Pseudo-
nitzschia HAB event. Data integration and high frequency sampling greatly increase the
ability to monitor bloom development. In situ genetic sampling by the moored ESPs
verified the presences of a subsurface Pseudo-nitzschia population. The glider
observations detailed the upwelling transport of deep nutrient rich waters along with the
subsurface phytoplankton communities, which resulted in a surface Pseudo-nitzschia
bloom. These results revealed for the first time that upwelled subsurface phytoplankton
populations can initiate surface HAB expressions in the region.

36

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43

Table
1.
Domoic
acid
concentrations
from
barnacles
collected
from
the

exterior
of
the
glider
throughout
glider
deployments.

Deployment
–

Recovery
Date

Barnacles

weight
(g)

Barnacle
Tissue

Domoic
Acid
Concentration

(µg
g
-‐1
)
±
sd

24
March
-‐
19
April
2.16
(2
samples)
0.32
±
0.05

23
April
-‐
19
May

1.80
(1
sample)
1.75

24
May
-‐
17
June

0.32
(1
sample)
0.44

44

Figure 1. Map of the Southern California Bight (SCB) and the small rectangle marks the
study area (top). Lower planel shows the Central Southern California Bight , San
Pedro Channel, with locations of the glider track indicated by the dashed line
pattern, the MBARI EPS mooring locations by the gray circles, the Newport Pier
by the gray star, and the OCSD outfall pipe north by the dash-dot lines. The
letters (A-F) on the glider pattern indicate turning points and are used to clarify
glider transect locations throughout the manuscript.
Figure 2. The temeperature versus PO
4
and NO
3
concentrations from the 2010 CalCOFI
winter and spring cruises data sets in the Central SCB. The solid, vertical black
line indicates 13.5°C.
Figure 3.The times series of Newport Pier automated pier station surface temperature and
subsurface ESP ctd temperature data. The 13.5˚C is indicated by the horizontal
dashed line. Pseudo-nitzschia abundances from discrete weekly surface samples
at Newport Pier are shown separated into seriata class and delicatissima class.
The ESP SHA probes produced CCD values for combined P.
multiseries/pseudodelicatissima and P. australis relative abundance at
ESPnearshore and ESPoffshore. All Pseudo-nitzschia abundances are below
detection 18 April.
Figure 4. San Pedro Bay regional glider time series showing (A,C,E) temperature and
(B,D,F) chlorophyll fluorescence from 23 April to 7 May. For each time period
the top image in each panel shows the curtian plot of the region and the lower
image is the southernmost transect rotated to display as a flat section (line EF
details Fig 1). The white line is the 13.5˚C isotherm, a proxy for the top of the

45

nutricline. The tan areas indicate bottom topography. The red lines extending
along the bottom from the coast show the location of the OCSD outfall pipe.
Figure 5. MODIS images of sea surface temperature (A, C) and chlorophyll a (D, E) from
San Pedro Bay for 19 April and 24 April. The glider track and the OCSD outfall
are indicated by dashed black lines, black dots indicate ESP mooring locations
and the Newport Pier is indicated by the star symbol. (Details in Figure 1). Panel
E shows the MODIS chlorophyll image overlaid 3-dimensionally on the
southernmost glider transect, line E-F, from 27 April demonstrating the continuity
between subsurface and surface phytoplankton communities, as well as the
consistency between and in situ and remotely sensed chlorophyll.

46

Figure 1

47

Figure 2.

24.8
kg
m
-‐3

A

B

48

Figure 3.

49

Figure
4.

50

Figure
5.

51

Chapter 2: Pseudo-Nitzschia bloom initiation in the Southern California
Bight; Multi-year local and regional analysis of glider, satellite, and
surface current data.

Abstract
Two multi-month field efforts in 2013 and 2014 were conducted in the central Southern
California Bight to better understand the initiation and evolution of phytoplankton
blooms in the region with a focus on the genus Pseudo-nitzschia, a toxin-producing
diatom. Webb Slocum glider deployments combined with moored environmental sample
processors (ESPs), MODIS Aqua remote sensing, and a variety of supplementary data
sets were combined to enable an increased understanding of the development of harmful
algal blooms (HABs). The southward advection and subsequent retention of
phytoplankton communities in the coastal region was with a primary driver of Pseudo-
nitzschia toxic bloom events. Similar cell abundances were observed in both 2013 and
2014, but interestingly, toxin concentration differed by an order of magnitude between
the two observation periods. This may be explained by the consistent input of upwelled
nutrient-rich waters in 2014, which resulting in a less toxic population. This unique
dataset also demonstrated a connection between surface and subsurface phytoplankton
communities, where the subduction of a surface Pseudo-nitzschia population led to the
initiation of a subsurface toxic bloom. Overall, understanding the onset of HABs was
shown to be the result of a complex combination of local and regional dynamics.

Keywords: phytoplankton; harmful algal blooms; subsurface chlorophyll maximum;
Pseudo-nitzschia; gliders.

52

Introduction
Harmful Algal Blooms (HABs) are apparently increasing in intensity, toxicity, and
duration globally (e.g., Anderson et al., 2002; Gilbert et al., 2005). Although HABs are a
naturally occurring event, recent observed increases in their frequency and the negative
economic consequences associated with these blooms has sparked intense research efforts
to better understand the causative factors of bloom initiation and dissipation.
Throughout the Southern California Bight (SCB) HABs have been associated with the
genus of neurotoxin producing pennate diatom, Pseudo-Nitzschia (Busse et al. 2006,
Anderson et al, 2006, 2009, Schnetzer et al., 2007, 2013, Sekula-Wood et al., 2011).
The Pseudo-Nitzschia genus contains many species that produce the neurotoxin domoic
acid (DA), which causes domoic acid poisoning, also known as amnesic shellfish
poisoning (ASP). DA was discovered to be a threat to humans after 140 people became ill
due to mussel consumption in 1987 on the east coast of Canada (Wright et al., 1989). DA
also negatively impacts a wide range of wildlife including mussels, razor clams (Wekell
et al.,1994), marine mammals (Scholin et al., 2000), cormorants, and pelicans (Work et
al.,1993). Blooms of Pseudo-nitzschia can be expansive. A 1991 bloom extended from
Washington State to Southern California (Villac et al.,1993). In addition to the health
threats posed by these blooms, the economic implications can be extensive. For example,
high levels of DA have lead to the closure of shellfish collection and have caused
millions of dollars of economic losses along the Washington coast alone (Trainer et al.,
2009). Further details on Pseudo-nitzschia are well covered in recent extensive reviews
on Pseudo-nitzschia including its physiology, toxicity, and global impact of toxic events
(Anderson et al., 2012, Lelong et al., 2012, and Trainer et al., 2012).

53

A major goal of this effort was to better understand the initiation and evolution of HABs
in the SCB, specifically in the San Pedro Channel. This research was part of a large
NOAA funded Eco-HAB project, “ECOHAB: A Regional Comparison of Upwelling and
Coastal Land Use Patterns on the Development of HAB Hotspots Along the California
Coast.” The project was designed to address a series of hypotheses about HAB initiation
in the SCB with a particular focus on the toxic diatom, Pseudo-nitzschia spp.
The Eco-HAB proposal laid out clear hypotheses that were tested during the 2013 and
2014 field seasons. These included the following:
Hypothesis 1: blooms initiate as subsurface features (subsurface maxima) and eventually
manifest as surface blooms.
Hypothesis 2: blooms are predominantly the result of advective processes and retention
in eddy-like circulation; subsurface maxima are less important.
Hypothesis 3: there are a unique set of environmental conditions leading from bloom
initiation to toxicity that can be identified through a comparative approach, allowing us to
contrast potential factors (such as stratification, nutrient load, nutrient type) between
regions.
A secondary goal of the glider deployments was to seek evidence for the impact of
subsurface offshore effluent outfalls on the regional phytoplankton community. Howard
et al. (2014) compared sources of nitrogen into the coastal region and found that the
contribution of effluent might be significant in the San Pedro coastal region. The effluent
is especially enriched in nitrogen, but also phosphate and silicate (Petrenko et al., 1997,
Lyon and Sutula, 2011). These variables could influence the phytoplankton community
generally and the development of HABs particularly.

54

The present paper combines a variety of tools including gliders, moorings, MODIS
satellite data, and surface current mapping, over two multi-month field seasons, March-
May 2013 and 2014, to monitor the onset of HABS in the SCB. We show that the
southward advection and then retention of phytoplankton was associated with Pseudo-
nitzschia toxic bloom events. The sampling seasons were similar with respect to Pseudo-
nitzschia cell counts, but differed substantially with respect to observed concentrations
the DA toxin. In addition, a surface to subsurface connection of phytoplankton blooms
was observed, with a surface Pseudo-nitzschia bloom subducting below the surface and
initiating a subsurface toxic bloom event. The onset of HABs was shown to be due to a
complex mix of local and regional physical, biological, and chemical dynamics.

Methods
Location
The research in Southern California Bight (SCB) focused on the San Pedro
Channel (SPC) along the Orange County Coast south of the Los Angeles Harbor (Figure
1). The San Pedro Channel includes the area between Catalina and the mainland and
extends over the San Pedro shelf that extends from Los Angeles Harbor to near Newport
Beach. The shelf dynamics play an important role in the region’s physical and therefore
biological features. The SPC is a “hotspot” for Pseudo-nitzschia blooms in terms both of
Pseudo-nitzschia spp. abundance and toxicity (Schnetzer et al., 2007, 2013). The SPC
provides an opportunity to study HABs related to a mixture of both natural and
anthropogenic processes. The SPC is influenced by coastal upwelling, river runoff, as
well as anthropogenic inputs such as sewage effluent from the highly developed urban
coastline. The Orange County Sanitation District (OCSD) discharges approximately

55

5.3x10
8
L/day through the primary outfall diffuser located 7 km offshore at 56 m depth
and this offshore effluent pipe is included in the area of study (Figure 1).

Defining blooms
There are often inconsistencies in the use of the term “blooms” when referring to
phytoplankton communities. The definition can vary based on location, species, and
toxicity. Anderson et al (2009), which focused on the SCB, defined Pseudo-Nitzschia
abundances of less than 1x10
4
cells l
-1
, 1x10
4
to 1x10
5
cells l
-1
, and greater than 1x10
5

cells l
-1
, as low, medium, and high respectively with corresponding particulate domoic
acid (pDA) concentrations of less than 64 ng l
-1
, 64 – 500 ng l
-1
, and greater than 500 ng
l
-1
. The high pDA values were selected to correspond approximately with expectations of
elevated rates of DA-linked mammal stranding. The Anderson et al (2009) bloom
definition correspond relatively well with Seubert at al. (2013) who looked at anomalies
in weekly nearshore pier based surface samples of Pseudo-nitzschia spp. abundances,
chlorophyll a (chl-a) concentrations, and pDA concentrations. They defined a minor
bloom based on chl-a concentrations between 9.74 to 12.9 µg l
-1
and a major bloom as
greater than 12.9 µg l
-1
. Pseudo-nitzschia blooms were defined using abundances of
Pseudo-nitzschia seriata size class with minor blooms consisting of 4x10
4
to 8.8x10
4
cells l
-1
and major blooms greater than 8.8x10
5
cells l
-1
. Pseudo-nitzschia seriata size
class was the focus for blooms as opposed to total Pseudo-nitzschia cells, because toxic
blooms in Southern California are typically dominated by P. australis and P. multiseries,
both of which are part of the P. seriata size class (Anderson et al., 2006, Schnetzer et al.,
2007, 2012). In this paper “bloom” will follow the Seubert et al. (2013) convention
described above and focus on the P. seriata size class, because this definition was

56

developed for the SPC and corresponds well with the Anderson et al. (2009) definition
for the Santa Barbara Channel. The pDA levels of concern (low, medium, high) will
follow the Anderson (2009) toxin concentration, because it is based on potential impacts
to the biological community.

Slocum Glider Transects
This project utilized a pair of Webb Slocum G1 shallow-water gliders to sustain
repeated transects in the San Pedro Channel. Gliders are buoyancy-neutral autonomous
underwater vehicles (AUVs) that glide through the water by adjusting their pitch and
buoyancy using wings to transfer what would otherwise be vertical momentum into
horizontal movement. The gliders were deployed for extended periods of time enabling
them to provide spatial and temporal mapping of key variables. The gliders were
equipped with GPS positioning and Iridium communications enabling in-situ data
transmissions. The scientific instrumentation included a Sea-Bird conductivity-
temperature-depth sensor (SBE-41cp CTD) and WET labs ECO pucks optical
instruments. The optical sensors included three fluorometers with excitation/emission
channels that measured chlorophyll a (470nm/695nm), colored dissolved organic matter
(CDOM) (370nm/460nm) and phycoerythrin/ rhodamine (540nm/570nm), and an optical
backscatter sensor measuring at 3 wavelengths. The glider CDOM and chl-a fluorometers
were calibrated pre- and post-deployment using Sprite Zero for the CDOM calibration
and a local mixture of cultured phytoplankton species for chl-a calibration (Cetinić et al.,
2009). Gliders were recovered approximately every 23 days throughout the deployment
period for calibration, cleaning, and battery change and then returned to the transects
within 24 hours to minimize the gap in data. The glider calibrations were based at the

57

University of Southern California’s Wrigley Institute for Environmental Studies on
Catalina Island.
Although the gliders are not equipped with nutrient sensors, however, the nutricline in the
SCB has consistently been found to be associated with the 13.5°C isotherm (Armstrong
and LaFond 1966, Lucas et al. 2011, Seegers et al. submitted) Therefore, this temperature
proxy can be used as an indicator of the upper boundary of the nutricline.
The gliders were deployed on transects in the San Pedro Bay during 2013 and
2014. In 2013, the glider ran a box shaped pattern off the Orange County coast near
Newport Beach on and off the shelf in the area centered near the OCSD offshore sewage
effluent outfall (Figure 1). The total transect length of the Newport box was 47 km
taking the glider about 48 hours to complete a lap. The 2014 Newport glider transect was
adjusted to an “L” shape with a 14.5 km offshore leg and a 8.5 km along shore leg to
maximize coverage near the ESP moorings and along the shelf break (Figure 1). In both
2013 and 2014 a glider transect ran from the mainland near Palos Verde to Catalina
Island (PV-Cat line) covering 28km across the entrance into the San Pedro Channel
taking the glider about 1.2 days to complete a crossing (Figure 1). The primary analysis
in this manuscript will focus on the Newport transects with brief comments on the PV-
Cat line. Full analysis of the PV-Cat line will be presented in a paper by Teel et al. (in
prep).

Environmental Sample Processors
Two Environmental Sample Processors (ESPs) were moored near the glider
transect above the San Pedro shelf for the period of 7 March to 10 April 2013 and 1 to 30
April 2014 (Figure 1). The ESPs were equipped with a CTD (temperature, salinity, and

58

depth) and were set up to measure in-situ abundance measurements of potentially toxic
algae and pDA concentrations (Figure 1). The ESP is an electro-mechanical instrument
that filters seawater and either archives the filtrate for later analysis, or performs a variety
of analytical tests on board the device. For these field seasons, the instruments were
configured to detect several species of Pseudo-nitzschia and other HAB targets groups
using DNA probes targeted to sequences in the large subunit of the ribosomal gene
(Scholin 1997, Greenfield et al. 2006). The specific probes usedduring this deployment
included toxin-producing P. australis, P. multiseries, and P.
multiseries/pseudodelicatissima. The probes use a sandwich hybridization array that
produces spots of varying intensity depending on target concentration. The probe spot
intensity on a filter membrane compared to filter background as measured by a CCD
camera determines the presence and relative abundances of species (Greenfield et al.
2008). One ESP, “ESPoffshore”, (33.58°N, 118.03°W) was located offshore about 8 km
from the coast near the 60 m isobath with the instrument placed at a depth of 24 m
beneath the surface. A second ESP, “ESPnearshore”, (33.61°N, 118.02°W) was at the
30m isobath and placed about 8 m beneath the surface (Figure 1). The ESP’s moored
depths were selected in an attempt to sample the subsurface chlorophyll maximum
(SCM) based on previous field studies.

Southern California Coastal Ocean Observing System (SCCOOS) Data
The data collected during this project was augmented with harmful algal counts and
surface current data supported by the Southern California Coastal Ocean Observing
System (www.sccoos.org). SCCOOS provides a weekly service of HAB species
sampling from six piers including Newport Pier in our sampling area (33° 36′ N, 117° 55′

59

W). The weekly HAB counts separated Pseudo-nitzschia into two size classes;
delicatissima and seriata groups and we report the Pseudo-nitzschia seriata size class
abundance. In addition to cell counts supporting data encompassed several variables
including other HAB species, discrete surface chl-a concentration, continuous surface
temperature, and pDA. pDA is measured by filtering to 200 ml onto a glass fiber filter
(GF/F) and then it was tested for the presence of DA using an enzyme-linked
immunosorbent assay (ELISA; Mercury Science Durham, NC) with a limit of detection
of 0.02 µg l
-1
.
SCCOOS supports High Frequency (HF) Radar for surface current mapping along the
southern California Coast. The data is public available in a variety of resolutions and
formats (www.sccoos.org/data/hfrnet/). The daily surface currents from the region were
used in the paper.

MODIS
Sea surface temperature (SST) and chl-a concentration (chl-a) were analyzed from level 3
Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua data with 0.0125
degree pixel resolution obtained from the West Coast Regional Node of National Oceanic
and Atmospheric Administration (NOAA) CoastWatch
(http://coastwatch.pfeg.noaa.gov/coastwatch/CWBrowser.jsp). The MODIS data
expanded regional coverage and was used to monitor for surface physical events
including advection and eddies and biological features such as algal blooms.

Results
Pseudo-Nitzschia Abundance and pDA

60

March – May 2013
High levels of Pseudo-Nitzschia abundances and pDA concentrations were observed in
2013 (Figure 2). While no Pseudo-Nitzschia cells were counted at the Newport Pier on
11 and 25 March, positive Pseudo-Nitzschia counts occurred on the 4, 18, and 30 of
March at the Newport Pier with a range of 10,000 -13,000 cells l
-1
and discrete chl-a
concentrations of 0.83 – 2 µg l
-1
. Throughout March pDA concentrations remained below
12 ng l
-1
. April had much higher levels of Pseudo-Nitzschia and pDA with a peak on 2
April with 230,000 cells l
-1
, a pDA concentration of 2560 ng l
-1
, and chl-a concentrations
of 4.97µg l
-1
. The Pseudo-Nitzschia seriata counts decreased on 9 April to about 40,000
cells l
-1
and pDA concentrations to 51 ng l
-1
accompanied by a slight increase in chl-a
concentration to 5.24 µg l
-1
. On 15 and 22 April Pseudo-Nitzschia seriata abundance
increased again to major bloom levels of about 125,000 cells l
-1
with pDA concentrations
of 7420 ng l
-1
and 1230 ng l
-1
and corresponding chl-a concentrations of 2.79 and 4.3 ng
l
-1
, respectively.
The two ESPs were separated horizontally by 2 km and vertically by 16m, which resulted
in large difference between observations (Figure 3). ESPoffshore had no positive
Pseudo-Nitzschia counts and low to nondetectable pDA. In contrast ESPnearshore
throughout mid-March had P. australis abundances around 5,000 cells l
-1
with a mean
chl-a concentration near 10 µg l
-1
. On 1 April a large increase in P. australis and P
multiseries was observed with total abundance near 200,000 cells l
-1
, mean chl-a
concentration about 5 µg l
-1
, and pDA concentration of greater than 1000 ng l
-1
. Pseudo-
Nitzschia abundances remained elevated (10,000 – 30,000 cells l
-1
) at ESPnearshore until
ESPs stopped sampling on 3 April. ESPnearshore and the Newport Pier Pseudo-

61

Nitzschia abundances had similar trends and counts. However, the pier had nearly double
the concentration of pDA.

March to April 2014
In 2014 the Pseudo-Nitzschia event lasted 3-weeks and was characterized by
record setting Pseudo-Nitzschia abundances, but relatively low DA toxicity (Figure 2).
Newport Pier surface cell counts had about 40,000 Pseudo-Nitzschia cells l
-1
on 1 April
increasing to 325,000 cells l
-1
on 8 April and 47,000 cells l
-1
on 15 April with
corresponding pDA concentrations of 130 ng l
-1
on 8 April and 60 ng l
-1
on 15 April.
pDA was below detection on 1 April. The 8 April cell count of greater than 300,000 was
the highest Newport Pier Pseudo-Nitzschia cell count since counts started in 2008, but the
corresponding pDA was an order of magnitude less than the highest values sampled at the
pier.
The ESPs were deployed 1 April 2014 and both instruments detected low levels of toxins
immediately (Figure 4). The ESPoffshore had low to no counts of Pseudo-Nitzschia
throughout the deployment (not shown). However, ESPnearshore had the largest
abundances from 2- 11 April after which there was a steady decrease in Pseudo-Nitzschia
starting on 13 April following a pattern similar to Newport Pier abundances (Figure 4).
Low levels of pDA were measured at ESPnearshore from 1 – 15 April ranging from 20 to
220 ng l
-1
, with maximum pDA concentrations on 7 and 9 April as the Pseudo-Nitzschia
abundances began to decline.

Physical and Biological Features from Glider, Satellite, and Surface Currents
March – May 2013

62

The coastal ocean surveyed by the glider in 2013 during the late March pre-bloom
period had surface temperatures of 15 -16°C. A pre-bloom snapshot of conditions shows
stratification corresponding with a weak subsurface chlorophyll maximum (SCM) with
chl-a concentrations less than 3 µg l
-1
(Figure 5). The onset of the large Pseudo-
Nitzschia bloom began 1 April with an increase in subsurface chl-a concentrations off the
shelf associated with the 13.5 °C isotherm and the eventual shoaling of the this isotherm
to less than 10 m on the shelf, resulting in elevated chl-a throughout the top 20m. On 31
March on the shelf chl-a patches were present throughout the water column to the shelf
bottom (Figure 6). Although the deep cool isotherms shoaled to near the surface, the
surface layer remained warm with temperature greater than 16°C. The glider data
suggest that the shoaling isotherm could be associated with an internal wave leading to
high counts of Pseudo-Nitzschia at ESPnearshore and at the Newport Pier on 30-31
March (Figure 5). There is no surface signal of isotherm shoaling impacting the system
beyond the sudden appearance of modestly elevated chl-a 3 µg l
-1
in the surface layer.
The MODIS data from this period shows relatively warm nearshore waters coupled with
elevated chl-a concentrations (Figure 6). A week after the internal wave event, the
surface chl-a feature was lost and the dominant biological feature became the SCM with
concentrations greater than 8 µg l
-1
;

more than double the SCM chl-a concentration
throughout late March (Figure 5).
The vertically integrated currents from the glider showed interesting shifts during
this early April period associated with the onset of the Pseudo-Nitzschia event. After
relatively weak currents through March the overall current strength increased in April
(Figure 7). Particularly noteworthy are the nearshore currents that went from weak along
shore to strong onshore currents 29 March to 10 April.

63

A local upwelling event off the Palos Verdes peninsula resulted in cold water and
elevated chl-a mid-channel co-occurring with the nearshore high Pseudo-Nitzschia event
in early April. This event was captured in the 2 April MODIS ocean color image (Figure
6). This mid-channel feature was associated with a surface water temperatures of 15 °C,
which was 1-2°C cooler than surrounding sea surface temperatures. The cool mid-
channel water also had chl-a concentrations 4-7.5 µg l
-1
compared to 1.5 µg l
-1
of the
surrounding surface water. On April 6 the cool water and elevated chl-a associated with
the Palos Verdes upwelling was reduced in the near surface layer measured by MODIS
(Figure 6). However, the glider data shows that in the shallow subsurface 5 -15m
elevated chl-a greater than 8 µg l
-1
creating an SCM. On 6 and 7 April the SCM is
nearsurface enough that when displaced by an internal wave it resulted in a decrease in
sea surface temperature and elevated chl-a patches in the surface layer (Figure 6).
On April 8 the region experienced an advection event transporting cold water 12-
13 °C with relatively low surface chl-a (Figure 6). The regional connection seen in the
MODIS images suggest this feature is being advected into the system from the north.
This advected feature was observed to a 30 m depth with temperatures of 12-13°C
(Figure 8). Although MODIS data shows little chl-a being advected, the subsurface chl-a
was a prominent feature on the Newport transect and the PalosVerde to Catalina transect
with temperature ranging from 13-14°C and elevated chl-a 3.5 – 8 µg l
-1
to 40m (Figure
9).
The offshore feature began to move onshore on 10 April (Figure 10). The integrated
currents show dramatic changes during this period moving on shore and along shore to
the north, which is consistent with a retentive current pattern (Figure 9). Once the feature
moved nearshore the satellite images show the retention of the cool high chl-a waters in

64

the study area (Figure 11). This onshore movement of the offshore community and the
subsequent retention, corresponded with high abundance of extremely toxic Pseudo-
Nitzschia at the Newport Pier on 15 and 22 April of approximately 125,000 cells l
-1
with
pDA concentrations of 7420 ng l
-1
and 1230 ng l
-1
, respectively. The on-shelf surface
feature began to weaken on April 21 as the sea surface temperatures warmed and the
SCM became the dominant biological feature (Figure 12). The on-shelf surface
phytoplankton community dominated by Pseudo-Nitzschia on April 20 was physically
connected to the offshore subsurface chl-a community, and within days the SCM was
dominated by Pseudo-Nitzschia (Figure 8). The SCM on 22 April had chl-a
concentrations greater than 15 µg l
-1
and cruise data revealed that the phytoplankton
community was dominated by Pseudo-Nitzschia (Figure 12). OCSD cruise data from 24
April at 7 stations along the glider station showed that the SCM had mean Pseudo-
Nitzschia seriata abundances 8.1 x 10
5
± 3.3 x 10
5
cells l
-1
compared to the surface mean
abundance of 5.3 x 10
4
± 3.9 x 10
4
cells l
-1
. The station maximum for Pseudo-Nitzschia
abundances was 1.37 x 10
6
cells l
-1
The SCM was also highly toxic with a mean DA
concentration 4,000 ± 2.4 ng l
-1
and the surface DA concentration was an order of
magnitude less 290 ± 270 ng l
-1
. The SCM had evolved through out the March and April
with weekly SCM concentrations varying from less than 2 µg l
-1
to greater than 9

µg l
-1
(Figure 11).

March to April 2014
The 2014 Pseudo-Nitzschia event began early April with elevated Pseudo-Nitzschia at
the Newport Pier and at ESPnearshore (Figures 2, 4). An upwelling event began on
March 31 with tipping isopycnals causing nearshore temperatures to drop below 14°C

65

compared to warmer offshore sea surface temperatures ranging from 15 to 16°C. This
pattern was seen in both the San Pedro and PV-Cat gliders (Figure 12) as well as in
MODIS images (Figure 13). At the onset of the upwelling event the region was
dominated by low chl-a waters (<1 µg l
-1
) with patches of elevated chl-a (Figure 13).
Patterns in the region changed dramatically on 4 April with a high chl-a and low
temperature feature advected from the north. On-shelf and the near shore region had
elevated chl-a throughout the surface 15 m (Figure 12). The PV-Cat glider showed
tipping isopycnals associated with local upwelling in addition to the cold chl-a rich water
advected from the north with chl-a concentrations from 4-9 µg l
-1
through the surface 25
m (Figure 13). The north to south connection is evident in the MODIS figures from 5
April with sea surface temperatures of 14°C associated with elevated surface chl-a
concentrations (10 to 20 µg l
-1
) throughout the SCM (Figure 15). Integrated glider
currents from this early April period were very weak in the area suggesting little
advection out of the system (Figure 16). Surface currents estimated by HF radar in the
region showed strong southward currents (30 – 50 cm l
-1
) entering the San Pedro bay
from late March until April 5 (Figure 17). An overall weakening of surface currents was
seen in the region starting on 5 April accompanied by a change in flow directions with
the development weak on-shore flow near Newport. These onshore currents allow for
retention in the region. An area of elevated chl-a and cold water was maintained along
the Newport coast on the San Pedro shelf, as observed in the MODIS image (Figure 14).
During this retentive period Newport Pier had the highest Pseudo-Nitzschia on record
with over 300,000 cells l
-1
, but relatively low pDA.

Influence of Plume on Phytoplankton biomass and distribution

66

The OCSD effluent plume can be followed using glider CDOM fluorescence as a passive
tracer. The effluent plume typically is located deeper than the bulk of phytoplankton
(Figure 5, 8, 12). However, occasionally the effluent is found on the shelf near the
bottom at 30 m depth as is demonstrated on 21-22 April 2013 (Figure 8). In late April
2014 there was clear evidence of the on-shelf CDOM effluent feature directly interacting
with the phytoplankton on the shelf (Figure 12).
In 2013 and 2014 mean profiles were created for on-shelf (<60m) and off-shelf (>60m)
profiles and all glider profiles were analyzed for plume presence and absence throughout
the profile. Once characterized as “plume- present’ or ‘plume-absent’ then entire profiles
could be analyzed and compared to look for influence of the effluent on phytoplankton
distribution and abundance. Mean profiles were created from profiles at least 7 km from
the outfall pipe. The distance (> 7 km) was selected because Todd et al. (2009) found in a
San Pedro Bay plume distribution study that 96% of plume-present profiles were less
than 6 km from the outfall and therefore profiles greater than7 km from the pipe were
selected. Plume-present profiles were defined as a positive CDOM anomaly of greater
than 1.25 QSE and a corresponding negative salinity anomaly less than -.04 using 1 m
binned depths.
In both years the majority of the present-profiles were found within 6km of the outfall
pipe (Figure 18). In 2013 159 of 1722 (9%) of on-shelf profiles were plume-present and
off-the shelf the number of plume-present profiles increased to 19% (290 of 1550). In
2014 413 of 3165 profiles (13%) were considered plume-positive and 100 of the 1534
off-shelf profiles (7%) were plume-present profiles.

Discussion

67

The 2013 and 2014 results demonstrated that physical events including advection and
retention are important drivers of Pseudo-Nitzschia events in the San Pedro Bay. In 2013
and 2014 the region had periodic advection of chl-a enriched waters from the north, with
chl-a concentrations often greater than 10 µg l
-1
measured to depths greater than 25m
(Figures 11, 18). The long distance transport of Pseudo-nitzschia has been shown to be
important in Pseudo-Nitzschia blooms in the northern section of the CA current along the
Washington coast (Trainer et al., 2002, Macfadyen et al., 2008). Studies there showed
that the offshore Juan de Fuca Eddy retains high abundances of Pseudo-Nitzschia and if
the eddy becomes “leaky” during a HAB, then the offshore eddy bloom can impact
coastal waters and be the source for near shore blooms (Trainer et al. 2002; Macfadyen et
al., 2008; Trainer et al., 2009). In the San Pedro region the source population is not an
offshore eddy, but rather phytoplankton communities advected from the north. The Santa
Barbara Channel is considered a hotspot for Pseudo-Nitzschia blooms (Fryxell et al.,
1997, Anderson et al., 2006) and in 2014 the the connectivity and transport from this
region into the San Pedro region was apparent (Figure 15). The Santa Monica Bay just
north of San Pedro Bay has also experienced Pseudo-Nitzschia related HAB events
(Shipe et al., 2008) and could be a potential local source for Pseudo-Nitzschia seeding
populations. In contrast, the importance of regional advection during the 2013 and 2014
Pseudo-Nitzschia events is unlike the Pseudo-Nitzschia bloom observed in 2010 when a
local upwelling event of subsurface Pseudo-Nitzschia communities into the surface layer
was shown to play a role in the bloom, with no apparent regional advection (Seegers et al,
submitted). The variety of trigger mechanisms within the same region confirms the
complexity of these HAB events.

68

The 2013 and 2014 observations suggest that after a phytoplankton population was
advected into the San Pedro Channel retention caused by the local circulation becomes
important for the development of high abundances of Pseudo-Nitzschia along the coast.
Analysis of surface and integrated subsurface currents showed that the region was
dominated by along-shore flow during the most intense advection periods and advected
features typically stayed offshore until a shift in currents occurred. The shift currents
resulted in onshore flow and retention in the area. The importance of retention has also
been shown in other regions within the California Current. Macfadyen et al. (2008)
focused on the Juan De Fuca Eddy in the northern section of the California Current and
found that when eddy surface circulation is more retentive HABs are more likely to occur.
In the Santa Barbara Channel, Anderson et al (2006) suggested that the retention of
phytoplankton plays an important role in Pseudo-nitzschia blooms and toxicity.
A comparison between 2013 and 2014 shows that these years had similar Pseudo-
Nitzschia abundances throughout the season, while DA concentrations were beyond an
order of magnitude less during 2014 relative to the extremely toxic 2013 season. In-situ
sampling has shown that Pseudo-nitzschia spp. abundances are not always correlated to
DA concentrations within the California Current (Trainer et al., 2002, Marchetti et al.,
2004, Anderson et al., 2006) and in San Pedro Bay specifically (Schnetzer et al., 2013,
Suebert et al., 2013). Schnetzer at al. (2013) showed some differences in Pseudo-
nitzschia spp. abundances between high toxic and low toxic events, suggesting that
species distribution with in the Pseudo-nitzschia genus could be important, but is unable
to be addressed with our data.
In addition to Pseudo-nitzschia community composition, physical features have been
shown to impact Pseudo-nitzschia bloom toxicity. Physical events such as upwelling

69

and eddies can impact the nutrient distribution and concentration in a region and Pseudo-
nitzschia spp. toxicity has been shown to be sensitive to a variety of nutrient limitations
and ratios in the central SCB (Anderson et al., 2006, Schnetzer et al., 2007, 2012).
Although both 2013 and 2014 Pseudo-nitzschia events resulted from an advection event
followed by retention, these events had some distinguishing characteristics. The most
toxic period during the 2013 event was late April near the end of a month of elevated
Pseudo-nitzschia abundances above 1x10
5
cells l
-1
. It is possible that the long retention
of phytoplankton in the area allowed for nutrient draw-down that impacted toxicity.
Anderson et al. (2006) found eddy retention of cells in surface waters could lead to
nutrient draw down and enhanced DA production. In 2014, a relatively low DA year, the
bloom was relatively short with only a single week having Pseudo-nitzschia abundances
greater than 1x10
5
cells l
-1
and therefore shorter phytoplankton retention time. In
addition, in 2014 upwelling was more frequent along the coast and these waters were
presumably nutrient-rich due to the low temperatures (<13.5°C, an estimate of the
nutricline temperature). These nutrient inputs could potentially explain the difference in
toxin levels between 2013 and 2014. In 2014, coastal upwelling was observed off the
Palos Verde peninsula and the Orange County coast. Nutrient enriched upwelling could
limit nutrient draw down even by a large phytoplankton community. In comparison,
2013 had only a single local Palos Verde upwelling event that impacted the mid-channel
area and resulted in temperature dropping below 13.5°C on April 8-9 (Figure 10),
corresponding to the single pDA measurement below 1000 ng l
-1
throughout the month of
April. Toxic Pseudo-nitzschia blooms often occur in the Santa Barbara Channel and the
2014 data suggests it could be a source for blooms down the coast (Figure 15). If
advected waters are exposed to upwelled nutrient rich waters along the coast it is

70

theoretically possible that this nutrient enhancements could influence the toxicity of the
Pseudo-nitzschia population as it moves southward.
The observations during the 2013 and 2014 seasons contrast with the spring 2010 season
when the surface expression of a Pseudo-nitzschia bloom appeared to be locally initiated
by transport of a subsurface Pseudo-nitzschia population upwelled into the surface ocean
(Seegers et al, submitted). Although the subsurface was not shown to initiate a surface
bloom in 2013 and 2014 connection between the subsurface and surface was apparent. In
2013 a surface bloom subducted resulting in a toxic subsurface Pseudo-nitzschia
population that was maintained after the surface bloom and dissipated. This seeding of
the SCM with a surface toxic bloom could create the necessary conditions that for an
upwelled SCM triggering a subsequent surface bloom. The pattern and intensity of
advection, retention, and upwelling would all influence HAB occurrences.
The San Pedro Shelf is an important feature in the region’s dynamics. In this study we
observed that the shelf break caused internal waves to be created and causing shoaling of
isopycnals. The shelf allowed colder, deeper water to shoal up into coastal regions with
significant mixing in shallow waters. The glider data also showed that shoaling
isotherms were often associated with higher chlorophyll concentrations, demonstrating a
link between physical forcing and the occurrence of HABs in this region. In the SCB
much of the water-column variability is related to the internal waves, which can cause
displacements of isopycnals that exceed 15 m and are associated with strong alongshore
and cross shore currents (> 0.25 m s
-1
) (Lerczak et al., 2003). Also, in the SCB internal
tides have been linked to tipping nitriclines that can significantly impact phytoplankton
community composition and coastal primary production (Lucas et al., 2003). Noble et al
(2009) showed that energetic internal waves on the San Pedro Shelf can transport

71

dissolved and particulate materials. Our results support that internal waves are influential
on phytoplankton distribution and on HABs initiation in the SPC.
The effluent plume tended to be deeper than the phytoplankton. However, there were
times when the effluent signal was seen close to the shelf and pushed up onto the shelf
where effluent was in close proximity or direct contact with the phytoplankton
communities. The location of plume-present profiles tends to be north of the outfall
plume. The area would be a good location for further studies looking at how effluent may
be impacting the local phytoplankton communities.

Conclusions
The understanding of Pseudo-nitzschia blooms requires determining the mechanisms of
how elevated populations of phytoplankton can develop in surface waters. The research
presented here demonstrated the importance of regional advection of chlorophyll-
enriched waters from the north into the San Pedro Bay. The advected high chlorophyll
concentrations were was not limited to the surface, but often was often observed to
depths greater than 25 m. A shift in currents from along-shore to onshore combined with
coastal retention led to the highest abundances of Pseudo-nitzschia along the coastal
region. The 2014 season had the highest Pseudo-nitzschia abundances, but overall low
DA toxicity. The impacts of upwelled nutrient-enriched waters could influence the
toxicity of the population, because Pseudo-nitzschia toxicity is sensitive to nutrient shifts
and ratios. A complicated and diverse set of potential triggers for Pseudo-Nitzschia
events are involved in HABs along the Southern California Coast.

72

Acknowledgements
Matthew Ragan, Elizabeth Teel, Xiao Liu, Carl Oberg, Dario Diehl, and Nick Rollins
were integral members of the glider team. Arvind Pereira assisted with computer
programming, glider operations, and data processing. In addition to glider operations
Nick Rollins assisted with Matlab coding and insightful conversations. Mattias Cape and
Randie Bundy for a thoughtful review of the manuscript and general awesomeness.
Captain Ray Arntz and Captain Kyaa Heller of the SunDiver assisted with glider
deployments. Jayme Smith provided the OCSD 2013 cruise data. We also thank the staff
members of the Wrigley Marine Science Center, especially Lauren Czarnecki, Kellie
Spafford, Captain Trevor Oudin, and Captain Gordon Boivin, for their consistent support
throughout the diversion glider effort. We worked closely with the Caron Lab at USC,
Raphe Kudela’s group at UCSC, Chris Scholin, John Ryan, Jim Birch, and the MBARI
ESP team, Southern California Coastal Water Research Projec (SCCWRP), Yi Chao,
modeler, at UCLA, and Greg Doucette at NOAA. This research was supported by
National Oceanic and Atmospheric Administration grants NA11NOS4780052 and
NA08OAR4320894. Additional glider operation funding came from National Science
Foundation grants to D. Hammond OCE-1260692 and to M.Prokopenko OCE-1260296.

73

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Southern California. Limnology and Oceanography.
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Figure 1. Southern California Bight Map with a square marking the study area (top left),
Point Dume to Newport Map showing glider transects off of Newport and between Palos
Verdes and Catalina Island (top right), individual field seasons Newport glider tracks in
the San Pedro Channel showing the glider transects and ESP mooring locations (black
diamonds) in 2013 (bottom left) and 2014 (bottom right). The bold red line is the OCSD
effluent offshore outfall. The 20 and 60 m isobaths are shown.

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Figure 2. Newport Pier 2013 and 2014 weekly surface Pseudo-nitzschia seriata size class
abundances (left axis) and pDA concentrations (right axis). Glider deployment dates are
marked by light shaded grey rectangles.

Figure 3. ESP 2013 sandwich hybridization array estimated Pseudo-nitzschia abundances
and pDA (top) temperature (middle) and chlorophyll fluorescence (bottom) for
ESPnearshore at 10 m. Figure from MBARI.

81

Figure 4. ESP 2014 temperature and salinity (top), nitrate and oxygen, chlorophyll and
transmission, sandwich hybridization array estimated Pseudo-nitzschia abundances and
pDA (bottom) for ESPnearshore at 10 m. Figure from MBARI.

ESPs%
deployed%

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Figure 5. San Pedro Channel near Newport Beach temperature (right), chlorophyll
fluorescence (middle), and CDOM fluorescence (right) from glider for 29-30 March, 30-
31 March, and 31 March – 1April 2013. The white line is the 13.5 °C isotherm associated
with the top of the nutricline. The bottom bathymetry is shown in light brown. Each row
has a small map to show the glider location (thick black line), ESPs (black dots), OCSD
outfall (red line), 20 and 60m isobath (light grey), and Newport Pier (star). An internal
wave displacing the isotherm nearly 20m causing a near surface shoaling of isotherms
nearshore and elevated chlorophyll is seen throughout the surface layer on 30-31 March
(middle row).

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Figure 6. San Pedro Channel chlorophyll (left) and sea surface temperature (right) from
MODIS Aqua from 2013 2 April (top), 6 April (middle), and 9 April (bottom). The PV-
Cat and Newport glider transects are show in black. The Newport pier is located with a
grey star. The OCSD outfall is shown in black coming offshore.

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Figure 7. Vertically integrated currents near Newport Beach region of the San Pedro
Channel during the 2013 observation period. Integrated currents estimates are created
each time a glider surfaces. A vector representing a current of 0.1 m s
-1
is shown in the
upper right.

85

Figure 8. San Pedro Channel near Newport Beach temperature (left), chlorophyll
fluorescence (middle), and CDOM fluorescence (right) from a variety of April 2013 dates
on left. The white line is the 13.5 °C isotherm associated with the top of the nutricline.
The bottom bathymetry is shown in light brown. Each row has a small map to show the
glider location (details Figure 5). 6 April 2013 the subsurface chlorophyll maximum is a
dominant biological feature established above and below the 13.5°C isotherm. The black
circle indicates a surface cool water and chlorophyll feature.

86

Figure 9. Palos Verdes to Catalina temperature (left) and chlorophyll (right) from the
glider transect on north end of the San Pedro Channel from 9 -11 April 2013. Catalina
and Palos Verdes are labelled.

87

Figure 10. San Pedro Channel chlorophyll (left) and sea surface temperature (right) from
MODIS Aqua from 16,17,18, 20 April 2013. The PV-Cat and Newport glider transects
are shown in black. The Newport pier is located with a grey star. The OCSD outfall is
shown in black coming offshore.

88

Figure 11. San Pedro Channel near Newport Beach weekly mean glider profiles of
chlorophyll fluorescence (top) and temperature (bottom) from 2013 (left) and 2014
(right). Color represents date.

89

90

Figure 12. San Pedro Channel near Newport Beach temperature (right), chlorophyll
fluorescence (middle), and CDOM fluorescence (right) from the glider for a variety of
March –April 2014 dates from glider. (details Figure 5)

91

Figure 13. Palos Verdes to Catalina temperature (left) and chlorophyll (right) from the
glider transect on north end of the San Pedro Channel from 30-31 March and 2-4 April,
2014. Catalina and Palos Verdes are labelled.

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Figure 14. San Pedro Channel chlorophyll (left) and sea surface temperature (right) from
MODIS Aqua from 2,3,5,7 April 2014. The PV-Cat and Newport glider transects are
show in black. The Newport Pier is located with a grey star. The OCSD outfall is
the black line coming offshore near Newport Pier.

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Figure 15. Southern California Bight (left) and sea surface temperature (right) from
MODIS Aqua from 5 April 2014 demonstrating regional connectivity. The PV-Cat and
Newport glider transects are show in black. The Newport Pier is located with a grey star.

94

Figure 16 Vertically integrated currents near Newport Beach region of the San Pedro
Channel during the 2013 observation period as estimated by the glider a surfacings. A
vector representing a current of 0.1 m s
-1
is shown in the upper right.

95

Figure 17. San Pedro Channel 6km 25 hour average surface currents from March and
April 2014 from SCCOOS.

96

Figure 18. Location of plume profiles (light gray dots) and no-plume profiles (dark dots).
Shown are the OCSD offshore outfall (red) and the 20m and 60m isobaths.

97

Chapter 3: Glider and remote sensing perspective of the upper layer response to an
extended shallow coastal diversion of municipal wastewater effluent.

Submitted to Estuarine, Coastal and Shelf Science on October 15, 2014

Bridget N. Seegers
a*
, Elizabeth N. Teel
a
, Raphael M. Kudela
b
, David A. Caron
a
,
Burton H. Jones
a,c

a
Department of Biological Sciences, University of Southern California, 3616 Trousdale
Parkway, AHF 301, Los Angeles, CA 90089-0371

b
Ocean Sciences and Institute for Marine Sciences, University of California, Santa Cruz,
1156 High Street, Santa Cruz, CA 95064

c
Present address: King Abdullah University of Science and Technology, 4700 KAUST,
23955-6900, Thuwal, Kingdom of Saudi Arabia

* Author for Correspondence: seegers@usc.edu

98

Abstract
For a 3-week period in September 2012 the Orange County Sanitation District (OCSD)
diverted its wastewater discharge (5.3x10
8
L/day) from OCSD’s primary deep (56m)
outfall, 7 km offshore, to a secondary shallower (16 m) outfall 2 km offshore. It was
predicted that the low salinity and low density of the effluent would cause it to rise to the
surface with limited dilution, thus elevating the surface nutrient levels in the well-lit
shallow waters and stimulating significant algal blooms in the region surrounding the
nearshore discharge. To acquire high spatial and temporal coverage of the affected region
before, during, and after the wastewater diversion, three Teledyne Webb Slocum gliders
and a Liquid Robotics surface wave glider were deployed on transects near the outfall
pipes. The combined AUV and remote sensing dataset indicated that the phytoplankton
abundance increased in the upper layer in response to the diversion, but that the
magnitude of the response was less than expected and was spatially patchy. Variation
between predicted and observed phytoplankton response may be attributed to unexpected
high rates of dilution after effluent emission, such that at times the effluent plume was
mixed throughout the upper 20 meters and occasionally through the upper 40m.
Following the diversion, the system returned to conditions similar to pre-diversion
conditions within 72 hours.

Key Words: phytoplankton; waste-water treatment; sewage; outfalls; AUVs; Southern
California Bight

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1. Introduction
The Southern California Bight coastline runs about 700 km from Point Conception in the
north to San Diego in the south. The coast is highly impacted by human activities with
nearly 20 million people in the region. One large anthropogenic input into the coastal
system is treated sewage effluent, which enters the ocean from subsurface and offshore
ocean outfall pipes. The outfall pipes have been designed to minimize the effluent
impacts on the coast. Occasionally these primary outfall pipes need to be repaired, and
during the repairs the effluent is often redirected to outfalls that are shallower and closer
to shore. The Orange County Sanitation District (OCSD) needed to repair their primary
offshore deep outfall in September 2012, therefore, for 3 weeks all effluent was diverted
to a secondary shallow nearshore outfall.
The effluent’s buoyancy, due to low salinity and density, was expected to transport
nitrogen-rich effluent into the surface waters with reduced dilution, which would bring
nutrients into the well-lit, nutrient-depleted shallow waters with the potential to stimulate
algal blooms. The City of Los Angeles carried out a similar diversion in November 2006
into Santa Monica Bay (65 km north of OCSD) with a comparable rate of effluent
discharge. Although the L.A. city diversion lasted only 50 hours the subsequent
phytoplankton bloom was dominated by Cochlodinium sp., a toxic dinoflagellate, and
reached chlorophyll concentrations up to 100 µg l
-1
(Riefel et al 2013). It was expected
that the OCSD diversion could have similar consequences. Concerns about harmful algal
blooms and coastal water quality led to an intense monitoring and research effort.
The diversion not only provided the opportunity to study the effects of relocating the
effluent discharge nearshore in shallower waters, but allowed us to examine the effect of
turning off the offshore, subpycnocline discharge. The steady input of nutrient rich

100

waters has been shown to be an important nutrient source in the local area (Howard et al.
2014). The temporary removal of the offshore, subsurface effluent nutrient source
provided a unique opportunity to observe the response of a system that typically has a
large, continuous, and potentially influential anthropogenic input.

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2. Location and Methods
2.1 Location
OCSD discharges its treated wastewater into San Pedro Bay off the coast of Orange
County, located in the central Southern California Bight (Figure 1). OCSD typically
discharges approximately 5.3x10
8
L/day through the primary outfall diffuser located 7
km offshore at 56 m. From September 11, 2012 to October 3, 2012 OCSD completed a 3-
week diversion of their effluent to a shallower (16 m) outfall located 2 km from shore.
The response to this large nutrient addition to the shallow nearshore and near surface
waters was closely monitored. The effluent is especially enriched with nitrogen with
nitrogen to phosphorus ratio (N:P) often near 100:1 and concentrations of ammonia
around 2.1 mmol l
-1
and phosphate 8.5 µmol l
-1
(Lyon and Sutula, 2011). Additionally,
silicate is often found in sewage effluent with concentrations of greater than 550 µmol l
-1
(Petrenko et al., 1997). Table 1 summarizes nutrient concentrations of pure OCSD
effluent, 100:1 effluent dilutions, and in-situ coastal water from a pre-diversion cruises. A
full summary of nutrients from the OCSD diversion is covered in Caron et al. (this issue).

2.2 Slocum and Wave Gliders
During OCSD’s diversion a combination of Teledyne Webb Slocum gliders and a Liquid
Robotics surface Wave Glider were deployed on transects near the outfall pipes to
provide spatial and temporal characterization of the region’s biology and physical
structure before, during, and after the diversion event. Gliders are an effective tool for
tracking effluent plumes, especially, because the patchy nature of the response makes it
difficult to track the plume with traditional boat sampling transects (Rogowski et al.,
2013).

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The Slocum gliders were equipped with a flow-through Seabird CTD, WET labs ECO
Puck Fluorometer (excitation/emission), Chl-a (470/695 nm), color dissolved organic
matter (CDOM) (370/460 nm), Phycoerythrin (540/570 nm), and WET labs ECO Puck
Backscattering Sensor at 532, 660, and 880 nm. The estimated vertical resolution of
glider fluorescence and backscattering ECO Pucks was 30 cm and the CTD vertical
resolution was 60 cm. The horizontal resolution of a Slocum glider can be estimated as
three times the dive depth with an estimated horizontal speed of 0.3 m/s. Data was binned
to 1 m for use in profile analysis. The Slocum gliders were removed every 22-26 days
for a battery change, cleaning, and CDOM and chlorophyll calibrations following the
protocol described in Cetinić et al. (2009).
The Slocum gliders covered 3 different along-coast zigzag transects designed to
maximize spatial coverage and the time spent around the outfall itself. The Slocum
gliders profiled from the 3 to 90 meters or 5 meters from the bottom when on the shelf.
Two glider transects covered the nearshore from approximately the 20 meter isobath to
beyond the shelf break offshore. OCSD-N covered an alongshore distance of 12 km
north/northwest of the outfalls and OCSD-S covered a distance 17 km downcoast from
the outfalls. The alongshore coverage was greater to the south, based on the expectation
that late summer, nearsurface currents tend to be to the south (Dong et al 2009, Hamilton
et al 2006, Noble et al 2009). The OCSD-N and OCSD-S transects overlapped near the
outfalls to maximize coverage (Figure 1). A third glider transect, OCSD-O, covered the
offshore region up to 20 km from the nearshore outfall (Figure 1).
Wave Glider SV2 by Liquid Robotics uses ocean wave energy for propulsion. The Wave
Glider was equipped with an above surface Airmar PB200WX weather station, a SeaBird
GPCTD, and a Turner Designs C3 Fluorometer measuring CDOM, chlorophyll, and

103

crude oil at 20 cm depth. The CDOM and chlorophyll fluorescence are reported in
relative fluorescence units (RFUs) to identify patterns and trends. CTD data collection
ceased after September 15
th
as the CTD was sheared off the Wave Glider. The Wave
Glider traversed a nearshore zigzag pattern that overlapped the Slocum glider OCSD-S
transect (Figure 1).

2.3 MODIS
Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua 250m ocean color
images provided expanded regional coverage of near surface chlorophyll and CDOM
throughout the event period. MODIS Aqua data were acquired as Level 0 files from the
NASA Ocean Biology Processing Group. Files were processed to Level 2 using SeaDAS
7.0 at 250 m resolution using NIR/SWIR atmospheric correction. The chlorophyll
concentration was calculated with the OC2 algorithm and the Quasi Analytical Algorithm
(QAA) model was used to estimate CDOM (a
g
) absorption at 443nm, which are products
derived from the inversion algorithm of Maritorena et al. (2002). MODIS 250m ocean
color images are touched on briefly here, but are covered in more details in Gierach et al.
(this issue).

2.4 Effluent Characterization for Tracking
The ability of gliders to track both the effluent plume and the plume’s potential
influence on the system depends on the reliability of identifying the plume in the water
column. A variety of approaches have been taken by previous researchers to map
effluent plumes. Early efforts relied on ammonium and coliform bacteria as an
unambiguous tracer for the plume because plume concentrations generally exceeded

104

ambient concentrations (e.g., Jones et al., 1987). Later work attempted to identify the
plumes on the basis of temperature, salinity, turbidity and chlorophyll fluorescence
anomalies relative to ambient characteristics (Washburn et al 1992, Wu et al 1994). In the
San Pedro Region studies have used a combination of salinity and fecal indicator levels to
track the plume (Jones et al., 2002). Todd et al. (2009) used a combination of glider
measurements of temperature, salinity, and density data to manually and automatically
detect plume-present profiles. The advancement of optical instruments and autonomous
research vehicles has broadened the tools available to track effluent plumes. More recent
work has shown that CDOM is a robust and reliable tracer at concentrations above the
ambient background (Petrenko et al 1997, Rogowski et al 2012; 2013). Rogowski et al.
(2012) used salinity, temperature, and CDOM measurements from an REMUS to
successfully track an effluent plume off the southern California coast near San Diego in
temporally and spatially variable coastal ocean. Their results showed that CDOM as a
tracer can track further than salinity gradients. In this study the glider data showed that
the effluent plume was identifiable by a low salinity and elevated CDOM signal in the
area near the OCSD outfall (Figure 2B,D). The inherent variability of vertical profile
structures made it difficult to identify the plume based on fixed salinity and CDOM
values. Instead we used corresponding salinity and CDOM anomalies in individual
profiles as evidence of the effluent plume presence in the profile. Representative mean
salinity and CDOM profiles were created for the area using profiles unaffected by
effluent. In order to avoid the effects of effluent on the representative mean profile we
used all glider profiles that were greater than 12 kilometers from the OCSD offshore
ocean outfall. Our approach followed a method similar to Todd et al (2009), which
focused on salinity anomalies to indicate effluent plume. Once mean profiles were

105

determined, individual profiles could be sorted and any profile that had a salinity
anomaly less than -0.04 (same salinity anomaly used by Todd et al., 2009) and a
corresponding CDOM anomaly greater than 1.25 ppb QSE was considered to have a
positive plume signal. The pre-diversion and post-diversion salinity and CDOM
anomalies had to be between 20-65 m to be considered an effluent plume signal this was
done to exclude the low salinity, high CDOM surface signal from rivers being incorrectly
labelled as effluent plume-present. Throughout the diversion the anomalies in the surface
30 m were considered effluent plume-present. This characterization of “plume-present”
profiles versus “plume-absent” profiles enabled tracking of effluent plume water
throughout the diversion. Unpaired 2-sample t-tests processed with Matlab were used to
test if the plume-present and plume-absent values were significantly different from one
another.

3. Results and Discussion

3.1 Pre-Diversion Conditions
The Slocum gliders began mapping the area nearly two weeks (August 29 to September
11) before the nearshore diversion began, providing a baseline for pre-diversion
conditions. A snapshot of pre-diversion conditions shows strong summer stratification
with surface temperatures of 18-22°C (Figure 2). Monthly sea surface temperature
climatologies (2003-2013) from MODIS Aqua showed September temperature were
above average with a SST anomaly of 1.37° C (Kudela et al., this issue). The
phytoplankton distribution was characterized by a subsurface chlorophyll maximum
(SCM) centered at 38.6 ± 6.8 m with a mean chlorophyll concentration of each profile

106

maximum of 6.0 ± 2.2 µg l
-1
(n=870) off shore of the shelf break (Figure 2). It shoaled to
27.6 ± 5.9 m over the shelf where the mean chlorophyll concentration of profile
maximums was 5.3 ± 1.8 µg l
-1
(n=923). The effluent plume, characterized by high
CDOM and reduced salinity, was very evident in the section nearest the primary outfall
(Figure 2), but can be seen extending in both directions along coast from the outfall. The
plots indicate that the effluent plume can disrupt the subsurface chlorophyll as the low-
chlorophyll effluent water enters into the water column. In Figure 2 both the center
section and the section to the northwest (left) show evidence of a reduction in the
chlorophyll fluorescence where the plume, as indicated by elevated CDOM, is present.
Elevated CDOM also appears near-bottom over the shelf. This near-bottom elevated
CDOM is associated with increases in backscatter (not shown) and therefore is particulate
in nature. This near-bottom CDOM could result from internal tides that carry the effluent
plume shoreward over the shelf. It may not necessarily be associated with effluent, but
related to resuspension of the bottom layer where there is organic matter that has similar
excitation/emission to effluent CDOM.
Elevated CDOM and reduced salinity anomalies were used to detect effluent in individual
profiles from the gliders, and thus identify individual profiles where effluent was present.
This enabled the horizontal mapping of the plume distribution based on these
characteristics. Of the total 1793 pre-diversion profiles, 534 (30%) were positive for the
presence of effluent plume, “plume-present”, and1259 (70%) were “plume-absent”, i.e.
not significantly different from ambient salinity and CDOM characteristics. Most of the
plume-present profiles were located on the shelf to the west northwest of the outfall,
however plume-present profiles were also found along the coast to the east/southeast of

107

the outfall and south and offshore of the outfall demonstrating that with time effluent
impacted profiles can be found throughout the study region (Figure 3).
The ability to track the effluent plume creates the ability to evaluate effluent impacts on
physical and biological aspects of the local ocean. The offshore ocean outfall pipe is at a
depth of 56m. The depth of the pre-diversion mean CDOM maximum in plume-present
profiles was 47 m and that value was used to estimate the depth of the effluent plume
(Figure 4). Both plume-present and plume-absent profiles had a mean subsurface salinity
minimum between 42-43 meters. However a t-test showed that plume-present profiles
(n=534) had a significant lower salinity at the subsurface minimum compared to plume-
absent profiles (n=1259) (p<0.05 at all depths).
The biological community was monitored using chlorophyll fluorescence measured by
the gliders as a proxy for phytoplankton biomass. Effluent is nutrient rich and its
presence in the euphotic zone could fuel phytoplankton growth especially during the low
nutrient and strongly stratified period of late summer. A two sample t-test showed that
the mean chlorophyll was significantly different (p<.05) for plume-present and plume-
absent profiles at all depths except from 36 -38 m and at depths greater than 80 m when
profiles ran together (Figure 4). The mean chlorophyll concentration was greater in
plume-present profiles at all depths less than 36 m. The plume-present mean SCM
(n=127) was at 32 m with Chl 4.3 µg l
-1
± 1.7, which was shallower than the mean SCM
no-plume profiles (n=735) with a SCM at 39 m with Chl 4.0 µg l
-1
± 2 (Figure 4). Below
38 m the plume-present profiles had mean chlorophyll concentrations significantly lower
than the plume-absent profiles. This deep layer low chlorophyll concentration could be
due the effluent entering the water column and disrupting the subsurface chlorophyll
layers (Figure 2).

108

The Wave Glider was deployed on September 7 for 4 days of pre-diversion surface
observations with measurement depths at 20-30 cm. Pre-diversion surface temperatures
ranged from 20 to 22 °C along the Wave Glider transect (Figure 5). On-shelf, both
temperatures and salinities tended to be lower than off-shelf measurements. Chlorophyll
fluorescence was elevated off-shelf in the vicinity of Newport Harbor from September 7-
9 in contrast with the on-shelf elevated chlorophyll fluorescence from September 9-11.
The CDOM fluorescence showed little pattern.
The pre-diversion MODIS Aqua 250m ocean color images from September 2 gave a
regional overview of nearsurface conditions. Nearsurface chlorophyll concentrations
were generally less than 1 µg l
-1
near the outfall pipes. CDOM absorption was also low
with values less than 0.1 m
-1
indicating low concentrations of CDOM (Figure 6).

3.3 Diversion Conditions
All of the glider profiles for the 22 day diversion period were complied into a mean
profiles for each variable to summarize diversion conditions. The warm surface waters
remained as in pre-diversion conditions (Figure 4). The chlorophyll profiles showed that
the subsurface chlorophyll maximum remained a dominant feature, but profiles also
showed elevated chlorophyll in the surface 20 meters (Figure 4). During the diversion
733 of the 2943 Slocum glider profiles had their maximum chlorophyll value in the
surface 20 m with a mean maximum surface chlorophyll value of 5.09 ± 2.75 µg l
-1
. In
addition to the elevated surface chlorophyll, the diversion profiles also show scattered
elevated CDOM fluorescence and reduced salinity in the surface 20m (Figure 4),
indicative of the presences of wastewater effluent in the upper layer during the diversion.

109

Although the regional response during the diversion was patchy, the increased
phytoplankton biomass appeared to respond directly to the presence of effluent plume
(Figure 7). A notable upper layer chlorophyll feature extended downcoast from the
location of the OCDS outfall during the period of September 29 to October 3 (diversion
days 17 – 22). Chlorophyll concentrations in this feature exceeded 8 µg l
-1
in the patch,
whereas chlorophyll fluorescence was less than 2 µg l
-1
in most of the surrounding
nearsurface region and less than 5 µg l
-1
in the subsurface chlorophyll maximum (Figure
7). The elevated chlorophyll directly coincided with the elevated CDOM and reduced
salinity of the effluent plume, demonstrating the phytoplankton community’s ability to
respond to the nutrients provided by the effluent input. The lower salinity effluent plume
feature also has a slightly lower temperature than the surrounding surface ocean water
leading to a minimal density difference between the effluent plume and ocean, which
would encourage mixing (Figure 7).
The profiles from throughout the diversion were separated into plume-present and plume-
absent profiles to examine the effluent influence on the coastal system. The majority of
plume-present profiles during the diversion were located on the shelf west northwest of
the outfall and showed a similar distribution as the pre-diversion plume-present profiles
(Figure 3). Plume-present profiles (n=1305) had significantly lower salinity and higher
CDOM in the surface 42 m compared to plume-absent profiles (n=1649) indicative of the
effluent signature. The plume-present profiles had significantly higher chlorophyll at all
depths in the surface 33 m layer compared to the no-plume profiles (t-test, p<0.05). The
absolute value of the increase in plume-present mean chlorophyll was depth dependent
and ranged from 0.14 µg l
-1
at 33 m to 1.77 µg l
-1
at 2m (Figure 4). Although the values

110

are modest it resulted in a 2-3 fold increase in mean chlorophyll at depths shallower than
14m (Figure 4).
Glider profiles from the diversion were compared to pre-diversion profiles to highlight
diversion influences on the system. There was a significant reduction in the intensity of
the SCM throughout the diversion (Figure 4). Pre-diversion SCM chlorophyll
concentrations were greater than 4 µg l
-1
regardless of plume-present or plume-absent
distinctions. The mean chlorophyll concentration of the SCM throughout the diversion
was less than 3 µg l
-1
.
A Wave Glider surveyed surface waters throughout the nearshore diversion area until
September 19. The patchy distribution of the plume and the patchiness of the surface
response of increased chlorophyll can also be seen in the Wave Glider data. The surface
effluent distribution indicated by elevated CDOM and reduced salinity, was patchy
throughout the surveyed area (Figure 5). Chlorophyll showed a delayed and limited
response as indicated by elevated chlorophyll RFUs occurring Sept 17-19.
MODIS Aqua 250m resolution ocean color images for chlorophyll and CDOM estimate,
QAA(a
g
) (443), clearly show the response to the diversion in elevated surface chlorophyll
and CDOM (Figure 6, September 20 and October 1). The response is very localized with
limited offshore and along shore transport. Chlorophyll and CDOM distributions follow
similar pattern in the region near the outfall pipe. The September 20 and October 1
images show the highest chlorophyll estimates on the shelf to the west/southwest and a
narrow band of elevated chlorophyll along coast to the southeast. CDOM indicative of
the surface effluent plume overlaps with the elevated chlorophyll. There is good
agreement between the MODIS elevated CDOM location and the general location of
many of the plume-present glider profiles (Figure 3).

111

3.4 Post-Diversion
The region quickly returned to pre-diversion conditions following the diversion. Glider
profiles from the 2 weeks post diversion showed a reduction in the surface chlorophyll
and CDOM (Figure 4). The SCM returned as the dominant biological feature at 28m,
which is 10 meter shallower than pre-diversion conditions. Along with a shallowing of
the SCM there was a reduction in chlorophyll concentrations from nearly 4 µg l
-1
during
pre-diversion conditions to 2.57 ± 2.3 µg l
-1
for plume-present and 1.89 ±1.843 µg l
-1

plume -absent mean profiles. A snap shot from October 5 -8, only 3-6 days after the
diversion, showed low surface chlorophyll throughout much of the region accompanied
by low surface CDOM concentrations (Figure 9).
The MODIS Aqua 250m ocean color images from October 8
th
showed neither elevated
chlorophyll nor elevated CDOM in the region near the outfall pipes (Figure 6) suggesting
the post-diversion surface conditions quickly returned to pre-diversion conditions.

4. Discussion
The diversion produced a local response to the nearshore effluent discharge, but the
response was very limited compared to pre-diversion expectations based in part on
previous effluent diversions in the region where chlorophyll concentrations exceeded 100
µg l
-1
(Riefel et al 2013). During the OCSD diversion, the maximum chlorophyll value
occurred in the upper 20 m in 25% of the glider profiles with a corresponding mean
maximum chlorophyll value of 5.09 ± 2.75 µg l
-1
. Likewise, elevated CDOM
fluorescence and reduced salinity were similarly observed in the upper 20 m of the water
column (Figure 4), indicative of entrainment of the effluent plume in the surface layer

112

during the diversion. Furthermore, profiles that showed evidence of being plume-present
had higher chlorophyll concentrations in the surface layer than plume-absent profiles.
Nonetheless, the response was limited and there are many possible mechanisms that
could explain the limited phytoplankton response.
High dilution rates would reduce the maximum nutrient concentrations and thus reduce
the system’s maximum potential phytoplankton response. The previously studied Los
Angeles Hyperion diversion into Santa Monica Bay was diverted to a pipe without
diffusers, which minimized initial mixing, created a concentrated surface plume and
triggered a significant phytoplankton response. The OCSD secondary diversion pipe
includes a 295 meter long diffuser section of the secondary outfall is outfitted 120 circular
effluent ports each with 15.9 cm diameter, which are designed to increase initial dilution
rates into the system (OCSD, 2009). The plume-present glider profiles, as indicated by
elevated CDOM fluorescence, showed that the plume was often mixed throughout the
surface 20 m (Figure 4). Warm water ambient ocean water conditions minimized the
density differences between effluent and the surrounding ocean and allowed for increased
mixing of low salinity effluent throughout the surface layer. A modeling study of
effluent dispersion in Santa Monica Bay and San Pedro Basin found that Santa Monica
Bay had a much higher retention rate than the San Pedro Basin, which could also
contribute to the higher phytoplankton biomass observed during the Hyperion diversion
(Uchiyama et al, 2014). Ohlmann (this issue) used Lagrangian drifters to follow the
plume and used CDOM and salinity values to estimate surface effluent dilutions of
greater than 100:1 within a kilometer of the secondary outfall pipe. A 100:1 effluent
dilution predicted surface nutrient values of 24.5 µM total inorganic nitrogen
(NO2+NO3+NH4) and 0.4 µM phosphate (Table 1). Nutrient concentrations throughout

113

the diversion were routinely lower than the 100:1 estimate with only 2 of 154 (1.3%) of
nitrogen measurements above 25 µM and 1 of 158 phosphate concentration above 0.6 µM
(Caron et al, this issue) suggesting dilutions rates greater than 100:1. In comparison to the
OCSD diversion the L.A. city Hyperion diversion had estimated initial dilution of 11:1
based on salinity measurements (Reifel et al., 2013). In addition to the physical
explanations for the limited phytoplankton response throughout the diversion possible
biological explanations include detrimental effects of excessive chlorination byproducts
in the effluent on phytoplankton growth rates (Kudela et al., this issue) and bacteria out
competing phytoplankton for nutrients (Caron et al., this issue).
The OCSD offshore outfall has been a continuous input to the coastal ocean for greater
than 40 years and the diversion and the sudden removal of that long-term subsurface
effluent discharge created a unique opportunity to examine the effects of the effluent on
the coastal ecosystem. The primary offshore outfall is at a depth of 56 m and during the
pre-diversion conditions the plume was found to reach density equilibrium at 47 m at the
25.4 kg m
-3
isopycnal based on the depth of the CDOM maximum. Our results are
similar to a previous statistical analysis of glider observations that found the plume sits
near the 25 kg m
-3
isopycnal (Todd et al., 2009) and a modeled plume study that found
plume stabilizing at a depth of 46 m ± 5 m (Uchiyama et al., 2014). The locations of
plume-present profiles were primarily on the shelf to the west northwest (Figure 3). The
modeling results and the integrated glider velocities (Farrara et al, this issue) showed
general surface and subsurface nearshore currents tend to be weak and variable, but when
currents near the pipe were strongest they were northward, thus transporting the effluent
plume towards the north. In addition, throughout the diversion ADCP current data

114

showed retention rates on the shelf were at least 48 hours in the area near the outfall
(Kudela et al., this issue).
Although the majority of the plume-present profiles were found on the shelf plume-
present profiles were also observed in a narrow band along the coast to the east/southeast
of the outfall. A few additional plume-present profiles were detected south and offshore
from the outfall demonstrating that the effluent could be dispersed throughout the region
(Figure 3). The plume-present locations align well with the elevated MODIS CDOM
distribution from the diversion period (Figure 6). The distribution of plume-present
profiles that we observed compare with the distribution observed by Todd et al. (2009)
and the modeling results for the plume dispersal by Uchiyama et al. (2014).
The comparison of pre-diversion mean profiles showed a significant shift in the depth of
the SCM in plume-present profiles, when compared with plume-absent profiles. The
mean depth of the SCM in plume-present profiles was of 32 m with a mean chlorophyll
concentration of 4.3 µg l
-1
± 1.7 (n=127), which was about 7 m shallower than the mean
SCM no-plume profiles SCM at 39m with a mean chlorophyll concentration of 4.0 µg l
-
1
± 2 (n=735) (Figure 4). This result suggests that the effluent could be contributing to
and modifying the distribution of the phytoplankton biomass.
Although the observed extent of plume-present profiles is limited, the effluent
could have a variety of potential effects beyond simply supplying nutrients, shifting the
vertical distribution of phytoplankton and increasing the biomass in the water column.
Phytoplankton community composition has been shown to be sensitive to anthropogenic
nutrient inputs into the coastal ocean that may shift nutrient ratios and forms (e.g. nitrate,
ammonia, or urea). In particular much research has been done on harmful algal bloom
(HAB) species, their sensitivity or affinity for anthropogenic nutrient inputs to shift in

115

community composition or increases in the toxicity of cells along the California coast
(e.g. Anderson et al., 2006, Kudela et al., 2008, Loureiro et al., 2009). Kinetics
experiments showed that a variety of HAB organisms can utilize nitrate, ammonium, and
urea, and a comparison of maximum uptake rates of nitrogen species showed many HAB
organisms, including L. polyedrum, prefer urea (Kudela et al., 2008). A L. polyedrum
red tide bloom in Southern California acquired 38% of its nitrogen demand from urea,
despite low levels of urea relative to ammonium concentrations (Kudela and Cochlan,
2000). Natural assemblages of the neurotoxin producing diatom, Pseudo-nitzschia, can
double their domoic acid production when they obtain nitrogen by utilizing urea, an
indicator of eutrophication, compared with either nitrate or ammonium sources (Howard
et al. 2007) Anderson et al. (2006) demonstrated that Pseudo-nitzschia’s neurotoxin
domoic acid production is sensitive to shifting macronutrient ratios. It is worth noting that
toxic blooms of Pseudo-nitzschia are a reoccurring problem in the San Pedro Bay area
where some of the highest DA concentrations per cell have been reported for natural
populations (Schnetzer et al., 2007; 2013). However, nutrient rich surface run-off events
are not strongly linked to Pseudo-nitzschia blooms along the southern California coast
(Anderson et al., 2008, Schnetzer et al., 2013). Howard et al. (2014) showed the regional
anthropogenic inputs from outfalls could be a major contributor to nitrogen in the San
Pedro Basin and therefore could potentially contribute to the region’s primary production.
The observations from this study indicate that subsurface anthropogenic inputs influences
the local subsurface phytoplankton population. Previous glider work in the San Pedro
Basin demonstrated that blooms of toxic Pseudo-nitzschia sp. can develop in the offshore,
subsurface region prior to their manifestation in the surface layer and/or near the coast
creating a link between the subsurface phytoplankton communities and surface blooms

116

(Seegers et al., submitted). More research is necessary in the San Pedro region to
determine if the outfalls are impacting the phytoplankton community composition,
toxicity, and the manifestation of HABs.

5. Conclusion

The OCSD three-week effluent diversion to a nearshore shallow outfall caused a modest
increase in chlorophyll throughout the surface 30 m. The overall phytoplankton response
was less than expected based on previous regional outfall diversions. The expected
concentrated surface effluent plume was rarely observed. Instead the effluent plume was
often mixed throughout the surface 20 m and at times down to 40 m as shown in reduced
salinity and elevated CDOM throughout the surface layer. The mixing and increased
dilution likely explains why the phytoplankton biomass increase was not as high as
observed in other diversions. The higher phytoplankton biomass distribution generally
followed the plume distribution pattern, but the highest chlorophyll concentrations were
not associated with highest plume concentration. The effluent itself lacked chlorophyll
and was shown to dilute the subsurface chlorophyll maximum as it initially mixed into
the coastal ocean. In addition to initial dilution of the effluent that limited phytoplankton
response there is evidence of chemical and biological controls. During the OCSD
diversion the effluent received enhanced chlorination and dechlorination, creating
byproducts that were shown to inhibit phytoplankton growth rates (Kudela et al, this
issue). Additionally, the bacteria responding to the effluent discharge may have
outcompeted the phytoplankton for nutrients (Caron et al, this issue). The observed

117

response to the nearshore, shallow discharge diversion event appears to have been the
result of a combination of physical, chemical and biological factors.

Acknowledgements
Matthew Ragan, Xiao Liu, Carl Oberg, Dario Diehl, Kendra Hayashi Negrey,
Christopher Wahl, and Evan Randall-Goodwin were integral members of the glider team
during the diversion. Arvind Pereira assisted with computer programming, glider
operations, and data processing. Nick Rollins assisted with Matlab coding. Captain Ray
Arntz and Captain Kyaa Heller of the SunDiver assisted with glider deployments. We
also thank the staff members of the Wrigley Marine Science Center, especially Lauren
Czarnecki, Kellie Spafford, Captain Trevor Oudin, and Captain Gordon Boivin, for their
consistent support throughout the diversion glider effort. This research was supported by
National Oceanic and Atmospheric Administration grants NA11NOS4780052 and
NA08OAR4320894, Orange County Sanitation District research funds, and the
University of Southern California Provost Fellowship.

118

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environmental conditions during a toxigenic Pseudo-nitzschia australis bloom in
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G, McLaughlin K., Sengupta, A. (2014). Anthropogenic nutrient sources rival
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122

Water Sample NH
4
(µM)
NO3
(µM)
N02
(µM)
PO4
(µM)
SiO3
(µM)
N:P
Pre-diversion Surface 1.39 0.23 0 0.2 4.19 8.1
Pre-diversion
Subsurface Chl Max
3.08 2.18 0.1 0.22 4.78 24.4
Pure Effluent 1690 336 104 22.1 585 96.4
Estimated Surface Dilution 100:1 18.9 4.5 1.1 0.4 10.2 57.5

Table 1. Nutrients from cruise data (11 September) in surface and subsurface chlorophyll
max before the diversion began compared with effluent nutrient and the expected
nutrients in plume after initial 100:1 diffuser dilution. (data adapted from Caron et al,
this issue).

123

Figure 1. A Map of the Southern California Bight with a square indicating project area.
A map of Slocum glider and Wave Glider transects in the San Pedro Bay off the coast of
Orange County near Newport Beach. The OCSD primary outfall is in red and the
secondary shallow pipe in bold black. The 20 and 60 meter isobaths are shown.

124

Figure 2. Pre-diversion Slocum glider curtain plots from August 29 to September 3
showing temperature (A), chlorophyll fluorescence (B), Sigma θ (C), CDOM
fluorescence (D), salinity (E), and a map of the curtain plot shown in dark grey with the
transects covered throughout the entire diversion sampling in light gray (F). The brown
color is the bottom bathymetry. The OCSD offshore outfall (red) and the nearshore
diversion outfall (bold black) are shown.

125

Figure 3. Pre-diversion, diversion, and post-diversion location of plume profiles (light
gray dots) and no-plume profiles (dark dots). Also, shown is the OCSD offshore outfall
(red), the nearshore diversion outfall (bold black), and the 20m and 60m isobaths.

126

Figure 4 Pre-diversion (left), diversion (center), and post-diversion (right) glider profiles
of temperature, chlorophyll fluorescence, CDOM fluorescence, and salinity of plume-
present profiles (light gray dots) and no-plume profiles (dark dots) and the mean plume-
present profile (solid line) and mean plume-absent profile (dashed line).

127

Figure
5.
Pre-‐diversion
and
diversion
Wave
Glider
maps
of
chlorophyll,
CDOM,
temperature
and
salinity
data
measured
at

20
cm.
The
OCSD
offshore
outfall
(red)
and
the
nearshore
diversion
outfall
(bold
black)
are
shown.

128

Figure 6. Pre-diversion, diversion, and post-diversion MODIS 250m ocean color
estimates of chlorophyll concentrations (left) and CDOM (a
g
) absorption (right) ocean
color estimates. The OCSD outfall pipes are shown in red and gray.

129

Figure 7. Diversion glider curtain plots from September 29 to October 3 showing
temperature (A), chlorophyll fluorescence (B), Sigma θ (C), CDOM fluorescence (D),
salinity (E). The map of the glider paths (F) shows the transects for these curtain plots in
in dark grey and transects for the entire diversion sampling in light gray.

130

Figure 8. Post-diversion glider curtain plots from October 5 -8 (3-6 days post-diversion)
showing temperature (A), chlorophyll fluorescence (B), Sigma θ (C), CDOM
fluorescence (D), salinity (E), and a map of the curtain plot shown in dark grey with the
transects covered throughout the entire diversion sampling in light gray.

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Asset Metadata

Creator Seegers, Bridget Noreen (author)

Core Title Phytoplankton bloom initiation in the Southern California Bight: a multi-year local and regional analysis

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Marine and Environmental Biology

Publication Date 01/29/2015

Defense Date 12/09/2014

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag gliders,harmful algal blooms,OAI-PMH Harvest,Southern California Bight

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Advisor Jones, Burton H. (committee chair), Caron, David A. (committee member), Hammond, Douglas E. (committee member), Kiefer, Dale A. (committee member)

Creator Email bridgetseegers@gmail.com,seegers@usc.edu

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