Thesis Defense by Victoria Dickey – November 30th


"The Distribution of Microplastics in Marshlands Surrounded by Agriculture Fields: Elkhorn Slough (CA)"
A Thesis Defense by Victoria Dickey

Geological Oceanography Lab

Zoom | Live-Stream | November 30th, 2022 at 4:00 pm PDT


Victoria joined Moss Landing Marine Labs in 2018 after earning a BS in Oceanography at Hawaii Pacific University. She is in the Geological Oceanography lab under Ivano Aiello’s advisement and has enjoyed building skills in GIS, grain size analysis, and operating the Scanning Electron Microscope. Victoria came up with the idea to sample sediment to find microplastics after driving past the fields of plastic mulch on her way to school every day. She is a strong advocate for ocean conservation and has played a role in the local chapter of the Surfrider Foundation as well as on the advisory council for the Monterey Bay National Marine Sanctuary. Victoria believes strongly in the necessity of communicating science and conservation to people of all ages and demographics and hopes to continue to build that skill in her future careers.

Thesis Abstract

The wide-spread use and subsequent recycling of plastics in the agriculture industry promotes improper disposal and poses a threat to important wetland habitats. When plastics degrade, they break up into smaller pieces that pose serious threats to organisms that ingest them and to habitats they settle in. This study quantifies the estimated concentration, types, and lengths of microplastics (< 5mm plastic particles) in the marsh environments of Elkhorn Slough, California’s second largest estuary. Replicate samples of marsh soil samples were extracted from seven Elkhorn Slough marshes at varying distances from the head and the mouth of the estuary and potential sources of agricultural plastic. Using a safe and cost-effective density separation technique, microplastics were separated from the soil, identified, and counted on micro-filters using a dissecting microscope, then further analyzed with a Scanning Electron Microscope equipped with an Energy-Dispersive Spectrometer (SEM/EDS) to analyze surface microstructures and the elemental compositions of the particles. Two main microplastic morphotypes, fragments and fibers were observed. The average concentration of microplastics estimated by this study is ~1600 particles per kg of wet soil, which is comparable to the average concentration of microplastics found in the sediment of the Venice Lagoon. Fragments are statistically smaller but more abundant (making up 85% of microplastics found) than fibers and with an average length of ~85 µm and ~500 µm respectively. Fragment lengths at agriculture sites are larger than the rest of the sampling sites, indicating a shorter residence time in these locations and highlighting agriculture plastics as a potential source. All microplastics found in collected samples exhibit signs of weathering, like pitting and fractures on the surface.  This study explores the particle size distributions of microplastics and the sediment they were sampled from to highlight the similarities in the physical influences controlling their distributions. Importantly, the federally protected Monterey Bay National Marine Sanctuary exchanges an extensive tidal range with Elkhorn Slough. This study identifies potential sources of microplastics to the Monterey Bay National Marine Sanctuary and the surrounding shores with an emphasis on the agriculture industry.

Thesis Defense by Hannah Bruzzio – August 30th (Zoom)


"Effects of Ocean Acidification and Hypoxia on Stress and Growth Hormone Responses in Juvenile Blue Rockfish (Sebastes mystinus)"
A Thesis Defense by Hannah Bruzzio

Ichthyology Lab

Zoom | Live-Stream | August 30th, 2022 at 2:00 pm PDT


Hannah Bruzzio is a graduate student in the Ichthyology Lab at Moss Landing Marine Labs. In the spring of 2018, she got her BS from the College of William & Mary in Williamsburg, VA. While there she completed her honor’s thesis researching particle interactions with the gill arch/gill raker morphology of the American shad to investigate the fluid dynamics of filter-feeding fish. She joined MLML in the fall of 2018. 
For her master’s thesis, Hannah looked at how the environmental stressors of ocean acidification and hypoxia affects the hormonal stress response of juvenile blue rockfish. In addition to her research, Hannah worked as the MLML Environmental, Health and Safety assistant under Jocelyn Douglas. She also designed the open house t-shirts for 2019, 2020 and 2022. She also volunteered at the Monterey Bay Aquarium where she worked with the jellyfish and schooling fish husbandry staff. In April of 2022, Hannah returned to the east coast to accept a job at the Institute of Marine and Environmental Technology (IMET) as the Senior Biological Technician for their Aquaculture Research Center (ARC) in Baltimore, MD. There she maintains populations of Atlantic salmon, Tilapia, Rainbow trout, Nurse Shark, Blue gill, Hybrid striped bass, Blue crab, White-leg shrimp and Zebrafish for use in a wide range of RAS-aquaculture based research projects.

Thesis Abstract

Global climate change is causing increasing ocean acidification (OA) and deoxygenation (hypoxia) of coastal oceans. Along the coast of California, where upwelling is a dominant seasonal physical process, these environmental stressors often co-occur and are intensified in nearshore ecosystems. For juvenile nearshore fishes, who spend a crucial developmental life stage in coastal kelp forests during the upwelling season, these stressors are experienced concurrently and may have large implications for fitness. Environmental stress can set off an endocrine response, which impacts physiology, energy allocation, growth, and behavior. To test the effects of climate change on juvenile blue rockfish, I measured the endocrine response to single and combined stressors of OA and hypoxia after one week of exposure. Assays of cortisol and IGF-1 hormone responses, served as proxies for stress and growth, respectively. Full organismal effects of environmental stressors were evaluated using a scototaxis (i.e., light/dark anxiety) behavior test, and measures of physiological changes in maximum metabolic rate (MMR) and body condition (i.e., Fulton’s K condition index). I found that peak (~1 hour) cortisol levels were highest in the single stressor low pH (7.3 pH), followed by the combined stressor (7.3 pH and 2.0 mg/L O2) and then the single stressor hypoxic treatment (2.0 mg/l O2). This high peak cortisol associated with low pH may indicate the role of cortisol in acid-base regulation. Only the low DO (dissolved oxygen) group did not exhibit a recovery of cortisol levels by the end of one week. There was no observable difference in IGF-1 in juvenile blue rockfish after a week of exposure to any of the pH or DO stressors. When cortisol levels were high, the same fish had low levels of IGF-1, and when cortisol levels were lower, the same fish had highly variable levels of IGF-1. At one-week of exposure, cortisol exhibited a positive relationship with MMR, such that higher stress levels were associated with greater oxygen consumption by the fish. MMR values themselves were highest in the low DO fish, which subsequently also had slightly higher cortisol levels at one-week. Juvenile blue rockfish were largely robust to any behavioral changes associated with stress across treatments. Hypoxic treatment fish had significantly lower body condition than fish from treatments with ambient DO levels after one week. Overall, the results indicated that pH levels influenced hormonal stress physiology, while DO levels contributed to observed differences in metabolism, body condition, and behavioral anxiety in juvenile blue rockfish. I was unable to tease apart and classify whether OA and hypoxia work in an additive, antagonistic, or synergistic way. Continued research should include more experimental stressor treatment levels of varying intensity of both individual and combined treatments as well as upwelling/relaxation fluctuating treatment levels. Elucidating the effects of climate change on fish endocrine response and physiology is important for fish population management and can help inform stock assessment models of blue rockfish in a rapidly changing ocean.


Hannah Bruzzio Presents: Effects of Ocean Acidification and Hypoxia on Stress and Growth Hormone Responses in Juvenile Blue Rockfish (Sebastes mystinus)

Thesis defense by Caroline Rodriguez – August 22nd (Zoom)


"Measuring the Impact of Thermal Stress on Coral Reef Resilience in Hawaii Using Large-Area Imagery"
A Thesis Defense by Caroline Rodriguez

Marine Environmental Physiology Lab | Invertebrate Ecology Lab

Zoom | Live-Stream | August 22nd, 2022 at 3:00 pm PDT


Caroline Rodriguez graduated from Duke University with a B.S. in Environmental Sciences in 2013 and completed internships at the North Carolina Coastal Federation and the Maryland Sea Grant Research Experience for Undergraduates (REU) program. After graduating, Caroline was chosen for the Chesapeake Conservation Corps program and spent two years working as a water quality technician and outreach coordinator for the Arundel Rivers Federation in Edgewater, Maryland. Caroline then spent two and a half years serving as a Peace Corps Volunteer in Nicaragua where she co-taught natural science courses in rural elementary schools and co-led environmental projects including school gardening and environmental summer camps. 

After the Peace Corps, Caroline began her M.S. in Marine Science in the Marine Environmental Physiology Lab at California State University Monterey Bay and the Invertebrate Ecology Lab at Moss Landing Marine Labs. Caroline was awarded the NOAA Center for Coastal Marine Ecosystems (CCME) Graduate Fellowship, which funded her thesis research. During her time in the CCME Fellowship program, Caroline completed a NOAA Experiential Research and Training Opportunity (NERTO) at NOAA Pacific Islands Fisheries Science Center in Honolulu, Hawaii where she developed a workflow to generate accurate growth, survival, and recruitment estimates for thousands of coral colonies using large-area imagery. She built on this work for her master’s thesis and investigated coral population dynamics for the dominant coral species across the Hawaiian archipelago and assessed the impact of thermal stress on coral populations. In addition to her research work, Caroline worked at the MLML Front Desk throughout her time at MLML, helped lead the Future Leaders in Marine Science mentorship program at the North Monterey County High School, and served as the CSUMB representative on the MLML Student Body. In 2022, Caroline was selected for the John A. Knauss Marine Policy Fellowship Program and moved to Washington, D.C. to work with NOAA’s Office of International Affairs. She hopes to continue working with diverse communities at the intersection of science and policy to advance equitable ocean and coastal policy.

Thesis Abstract

Coral reefs worldwide are declining due to several anthropogenic stressors, but rising ocean temperature is the most serious threat to coral reef persistence. Developing models that document changes in coral communities following thermal stress events and project trends in reef recovery is crucial in identifying resilient reefs. Traditional approaches to generating the coral vital rates necessary for demographic modeling are time consuming and field intensive; however, by leveraging Structure from Motion photogrammetry, we can accurately track populations over time at a large spatial scale. In this study, we assessed the population dynamics of the dominant coral species across the Hawaiian archipelago and investigated the impact of thermal stress on coral populations. The annual growth, survival and recruitment of 3,852 coral colonies (5,636 unique colony-level transitions) for 3 genera was recorded at 16 sites spanning the Hawaiian archipelago across 14 intervals from 2013 to 2019, including 3 bleaching events. These data were used to parameterize integral projection models to determine the impact of thermal stress on population growth. Degree Heating Week output from the NOAA Coral Reef Watch daily global 5km satellite was used to estimate thermal conditions at each site by calculating temperature stress severity (the mean of all maximum thermal anomalies) and frequency (number of thermal stress events per 10 years). We found that all three coral genera, which have different morphologies and life-history strategies, had negative population growth rates. As expected, smaller colonies experienced faster growth, but large colonies had a high probability of shrinking, due to partial mortality. Therefore, it may be biologically advantageous for larger colonies to fragment into smaller pieces and avoid total mortality. Population dynamics were primarily driven by coral growth and survival and should be targeted in future restoration and adaptation projects. Additionally, across all taxa, population growth rates (λ) varied spatiotemporally, but most sites exhibited a declining population growth rate (λ < 1). While increased severity and frequency of thermal stress events negatively impacted the population growth rate of massive Porites corals, there was no signal of this effect on encrusting Montipora corals. We demonstrate that despite variations in the responses observed among taxa, there is an overall expected population decline across the Hawaiian archipelago. While coral population growth rates are higher following bleaching events, signifying recovery, the projected increase in both the severity and frequency of thermal anomalies may overwhelm corals’ ability to recover and threaten coral population persistence.

Caroline Rodriguez Presents: “Measuring the Impact of Thermal Stress on Coral Resilience in Hawaii Using Large-Area Imagery”

Thesis Defense by Katie Neylan – August 12th (Seminar Room/Zoom)


"Evaluating a microalga (Schizochytrium sp.) as an alternative lipid source in fish-free feeds for sablefish (Anoplopoma fimbria) aquaculture"
A Thesis Defense by Katie Neylan

Ichthyology Lab

Zoom | Live-Stream | August 12th, 2022 at 1:00 pm PDT


Katie graduated from CSU Monterey Bay in 2016 with a B.S. in Marine Science. While there, Katie worked for a few MLML Ichthyology lab graduate students. Her undergrad research included two main projects: "Investigating the condition of surgeonfish along a nutrient gradient in the southern line islands" and "Examining the effects of size-selective mortality on sex change in a protogenous hermaphrodite species of goby, rhinogobiops nicholsii". Following her graduation, Katie worked for California Department of Fish and Wildlife (CDFW) as a Scientific Aid and collected data for the California Recreational Fisheries Survey in Santa Cruz, CA. 

Katie joined the Ichthyology lab at MLML in Fall 2018 and is co-advised by Dr. Scott Hamilton and Dr. Luke Gardner. Katie was awarded the California Sea Grant Graduate Research Fellowship in 2019, which funded her thesis research. For her thesis, Katie designed a feed experiment to test a microalga as an alternative lipid source in fish-free feeds for sablefish (Anoplopoma fimbria) aquaculture. She presented the results of her thesis research at the 2022 Aquaculture America conference. Katie is looking forward to pursuing a career in resource management and policy after completing her degree at MLML.

Thesis Abstract

Alternative feeds for finfish aquaculture are critical for the sustainable expansion of the aquaculture industry. Fish that are farmed for human consumption are often carnivorous; therefore, the industry uses wild-caught forage fish as a primary ingredient in farmed fish feeds in the form of fish meal (FM) and fish oil (FO). With the aquaculture industry expanding, alternative ingredients are needed to safeguard fisheries' sustainability and future aquaculture development. While some alternative feed ingredients have been identified, it is necessary to improve the existing options and identify alternative ingredients with higher concentrations of omega-3 polyunsaturated fatty acids (PUFAs). This study was designed with six feed treatments to test a microalga, Schizochytrium sp., as an alternative feed ingredient for sablefish (Anoplopoma fimbria). The two fish ingredient control diets are called +FM+FO (contains both FM and FO) and -FM+FO (contains FO). The fish-free diets completely replace FO with flax oil (FF Flax) or a combination of flax oil and low, moderate, or high inclusion of Schizochytrium sp. (FF LowSc, FF ModSc, and FF HighSc) in the feeds. After a five-month feeding trial, sablefish condition metrics, whole-body proximate composition, and apparent digestibility coefficients were not different across diet treatments. In contrast, sablefish growth was influenced by treatment, with the high microalga-inclusion diet (FF HighSc) performing as well as the fish-ingredient controls. Fillet fatty acid profiles were also influenced by diet treatment, generally reflecting the fatty acid profiles of the feed. Total PUFAs were higher in the fish-free diets than in the controls. These results suggest Schizochytrium sp. can increase PUFA concentrations in fish fillets, while not compromising fish health and growth, making it a viable ingredient for alternative sablefish feeds.


Thesis Defense by Alora Yarbrough – July 22nd (Livestream)


"The impacts of climate change on blackeye goby (Rhinogobiops nicholsii) stress responses, reproduction, and offspring fitness"
A Thesis Defense by Alora Yarbrough

Ichthyology Lab

Zoom | Live-Stream | July 22nd, 2022 at 4:00 pm PST


Alora Yarbrough is a graduate student in the Ichthyology Lab at Moss Landing Marine Labs (MLML). She received her BA in Biology from Pepperdine University in 2017. While there, she completed an undergraduate honor's thesis researching the effects of variable incubation conditions on the development of the California grunion which she presented at the Western Society of Naturalists Annual Meeting, the Joint Meeting of Ichthyologists and Herpetologists, and the Society for Integrative and Comparative Biology's Annual Meeting. After graduating, she completed internships with Heal the Bay at the Santa Monica Pier Aquarium and with Disney World's Animal, Science, and Environment Program in Florida. She then accepted a position in Dr. Scott Hamilton's lab at MLML in the fall of 2018.

For her Master's thesis, Alora examined how climate change affects the stress response, reproduction, and offspring fitness of blackeye gobies, a demersal reef fish common off the west coast of the United States and Mexico. In addition to her master's work, Alora joined the MLML IT department as a Help Desk Technician in 2019 through which she implemented projects such as the Student Life Website and headed the first media committee for the annual Open House fundraiser. In April 2022, Alora returned to southern California to join the Yelon Lab at the University of California, San Diego (UCSD) as a staff research associate supporting research investigating cardiac development in zebrafish.


Thesis Abstract

Climate change poses a major threat to marine ecosystems and the organisms living within them. Along with warming and sea level rise, the increasing intensity of ocean acidification and hypoxia events in coastal environments is of large concern. Weakened immune function, tissue damage, and altered reproductive output are only some of the detrimental effects of decreased pH in ocean waters. Hypoxia has also shown major consequences including decreased aerobic scope, altering predator-prey interactions, and inducing hyperventilation. Additionally, animals living in eastern boundary currents, such as off the coast of California, experience a regional phenomenon known as upwelling. As surface waters are directed offshore due to wind patterns, deep, acidic, hypoxic water is brought up to the surface magnifying the effects of ocean acidification and hypoxia for up to two weeks at a time. Both low pH and low amounts of dissolved oxygen (DO) characterize stressful conditions for many marine species. Under stress, one of the main hormones organisms will produce to maintain homeostasis is cortisol, therefore cortisol can act as a marker to determine the relative stress an animal is under. This study evaluated the stress response of adult female blackeye gobies when under both acute and chronic climate change stress by measuring muscular cortisol concentrations at specific time points while under one of four treatments: control (8.1 pH; ~9 mg/L O2), low DO (8.1 pH; 2.0 mg/L O2), low pH (7.3 pH; ~9 mg/L O2), and a combination of low DO and low pH (7.3 pH; 2.0 mg/L O2). In addition, the stress response differs for organisms at varying life stages. Notably, some larval fish species rely entirely on maternally derived hormones supplied by the yolk sac. An increase in cortisol in the yolk supply may impose developmental disadvantages on the larvae, but there is also evidence that it can better equip offspring to face the stressors experienced by their mothers. Therefore, the relationship between maternal and egg cortisol concentrations was investigated with females laying clutches under each of the four treatments. After laying, clutches were split to be incubated under the same conditions their mothers experienced or the control treatment. At 1 day post hatch, offspring physiological fitness was evaluated based on morphometric characteristics and standard metabolic rate. This study found adult female blackeye gobies experiencing acute stress tend to have higher cortisol concentrations than those under chronic stress. When evaluating how stress is translated generationally, a positive relationship between maternal and egg cortisol concentrations was found. However, blackeye gobies were not able to successfully fertilize eggs under the low pH treatment. In addition, clutches with higher initial cortisol concentrations showed trends of increased time to hatching and standard metabolic rate and decreased length and weight at 1 day post hatch. The results of this study suggest decreased pH and dissolved oxygen are harmful to both adult and larval blackeye gobies. Due to the disruption of successful reproduction under low pH and the developmental and physiological disadvantages under low DO, future populations of blackeye gobies could suffer greatly as anthropogenic climate change progresses.


Alora Yarbrough Presents: “The impacts of climate change on blackeye goby (Rhinogobiops nicholsii…

Thesis Defense by Rachel Aitchison – June 24th (MLML Seminar Room / Livestream)


"Redescription of Southwestern Indian Ocean guitarfishes Rhinobatos (Rhinopristiformes: Rhinobatidae)"
A Thesis Defense by Rachel Aitchison

Pacific Shark Research Center

Zoom | Live-Stream | June 24th, 2022 at 4:00 pm pst


Rachel graduated from the University of Oregon in December of 2018 with a B.S. in Marine Biology. While she was there, she spent three semesters at the Oregon Institute of Marine Biology (OIMB) exploring the tidepools, catching fish, and searching for whales. She also joined the Everblue team, a nonprofit organization that uses social media to share the latest marine science research, and spent a semester in the Maslakova lab working on a Nemertean DNA barcoding project. After graduating, she worked as a Teaching Assistant and joined the Pacific Shark Research Center in the fall of 2019.

For her thesis, Rachel analyzed the morphology of three Data Deficient species of guitarfish from the Southwestern Indian Ocean in order to revise their species descriptions. She presented this research at the American Elasmobranch Society International Wedgefish and Guitarfish Symposium, which she also co-organized, and the Northeast Pacific Shark Symposium. While at MLML, Rachel also helped with several student thesis projects including the surf zone Marine Protected Area (MPA) monitoring project and understanding salmonid environmental DNA (eDNA) movement in rivers. When she's not working, Rachel enjoys hiking, painting, and caring for her many plants. After graduation, Rachel is looking forward to moving back to the Pacific Northwest to ski, prepare for a PhD program, and get married.

Thesis Abstract

The shark-like rays (Rhinopristiformes) are found worldwide and are among the most threatened species of cartilaginous fishes. The guitarfishes (Rhinobatidae) are one of five families in this order, with many species being assessed as vulnerable, endangered, or critically endangered by the International Union for Conservation of Nature (IUCN). Current fisheries and conservation efforts are limited, however, due to unresolved taxonomic issues and poor species descriptions. Presently, there are three described species of Rhinobatos from the Southwestern Indian Ocean: Rhinobatos austini, R. holcorhynchus, and R. nudidorsalis. These three species of Rhinobatos are often mistaken for one another and are assessed as Data Deficient (DD). Until its description in 2017, R. austini was misidentified with the poorly defined, offshore occurring R. holcorhynchus. Rhinobatos nudidorsalis was described from a single specimen caught near the Mascarene Ridge in 2004, but may have been previously misidentified as R. holcorhynchus. The issue of misidentification is also often amplified by the lack of consistency in terminology and measurements for the Rhinopristiformes. Since the descriptions of R. austini and R. nudidorsalis, additional specimens have become available. Thus, a redescription of these three species is needed to clarify their taxonomic status. In addition, a guide to guitarfish morphology is needed to standardize measurements for this group by clarifying techniques and minimizing error across research groups.

            Several Rhinobatos species descriptions and FAO (Food and Agricultural Organization of the United Nations) catalogs for cartilaginous fishes were reviewed to describe and define guitarfish measurements. Morphometrics from four congener species of Rhinobatos from the Indian Ocean that have been assessed by the IUCN were analyzed and served as comparative material for the three DD species. In addition to the traditional morphological analyses used to distinguish guitarfish species, morphometrics from all seven species were analyzed using three multivariate statistics: a Non-Metric Multidimensional Scaling (nMDS), a Principal Component Analysis (PCA), and a Linear Discriminant Analysis (LDA). Results from the LDA show distinct clusters for species of Indian Ocean Rhinobatos and indicate that the oronasal region is effective in differentiating Southwestern Indian Ocean species. In addition, R. austini, R. holcorhynchus, and R. nudidorsalis are confirmed as distinct species and redescribed based on new material. These redescriptions provide taxonomic clarity for Southwestern Indian Ocean guitarfishes and will aid in species-specific identification, leading to improvements in conservation and fisheries monitoring and management.

Thesis Defense by Lauren Cooley – May 9th (Livestream)


"Research handling effects on stress hormones, blood parameters, and heart rate in juvenile northern elephant seals (Mirounga angustirostris)"
A Thesis Defense by Lauren Cooley

The Vertebrate Ecology Lab

Zoom | Live-Stream | May 9th, 2022 at 12:00 pm pst


Lauren Cooley is a graduate student in the Vertebrate Ecology Lab at Moss Landing Marine Labs (MLML). She received her BS in Animal Science from Cornell University in 2016 and completed internships at the Alaska SeaLife Center and Florida Fish & Wildlife Conservation Commission. After two years working as a marine mammal and sea turtle stranding technician at the Institute for Marine Mammal Studies in Gulfport, Mississippi, Lauren moved to California to join Dr. Gitte McDonald's lab group in 2018. Her research interests include the ecology, physiology, and conservation of marine mammals and sea turtles with a focus on animal welfare.

For her master's thesis, Lauren investigated the effects of research handling activities on stress levels in juvenile northern elephant seals using hormone, blood parameter, and heart rate data. She also worked as the Data Manager and later Stranding Coordinator for the MLML Marine Mammal & Sea Turtle Stranding Network. In addition to her research work, Lauren is passionate about science communication and served as MLML Social Media Coordinator, Editor of the MLML Drop-In Blog, and Outreach Chair for the Vertebrate Ecology Lab. In February 2022, Lauren moved back east to Cape Cod, Massachusetts to begin a new job as a Stranding Biologist with the International Fund for Animal Welfare (IFAW). She looks forward to a long career in the always exciting marine mammal stranding field and is very thankful for the opportunity to use her fieldwork and research skills in this new conservation-focused role.

Thesis Abstract

Wildlife researchers must balance the need to safely capture and handle their study animals to sample tissues, collect morphological measurements, and attach dataloggers while simultaneously ensuring their results are not confounded by stress artifacts caused by handling. To determine the physiological effects of research activities including chemical immobilization, transport, instrumentation with biologgers, and overnight holding on a model marine mammal species, I collected hormone, blood chemistry, hematology, and heart rate data from 19 juvenile northern elephant seals (Mirounga angustirostris) throughout a translocation experiment. Across my six sampling timepoints, cortisol and aldosterone data revealed a moderate hormonal stress response to handling that was accompanied by minor changes in hematocrit, blood glucose, and blood lactate, but not ketone bodies or erythrocyte sedimentation rate. I also performed the first assessment of heart rate as a stress indicator in this species and found that mean heart rate, interbeat interval range, and apnea-eupnea cycles were influenced by handling. However, by the time seals were recaptured after several days at sea, all hormonal and hematological parameters had returned to baseline levels and 95% of study animals were resighted in the wild up to two years post-translocation. Together these findings suggest that while northern elephant seals exhibit mild physiological stress responses to handling activities in the short term, they recover rapidly and show no long-term deleterious effects, making them a robust species for ecological and physiological research.

Lauren Cooley Presents: Research handling effects on stress hormones, blood parameters, and heart rate in juvenile northern elephant seals (Mirounga angustirostris

Thesis Defense by Juliana Cornett – May 6th (MLML Seminar Room / Livestream)


"Physiological Responses to Hypoxia in Juvenile Flatfishes"
A Thesis Defense by Juliana Cornett

The Ichthyology Lab | The Logan Lab (CSUMB)

MLML Seminar Room | Live-Stream | May 6th, 2022 at 4:30 pm

Juliana graduated from the University Honors Program at the University of California, Davis in spring 2018 with a B.S. in Biological Sciences. While there, Juliana participated in undergraduate research in the Grosberg Lab, where she assisted with a project on population genetics of symbionts hosted by sea anemones, and conducted an independent research project on symbiont photosystem performance for her undergraduate honors thesis. She also spent a semester studying abroad at the University of Queensland in Australia. After graduation, Juliana took a gap year, which included work in environmental education and volunteer work in museum education, before beginning her M.S. in Marine Science in the Logan Lab at CSUMB and the Ichthyology Lab at MLML in fall 2019. 

For her thesis, Juliana investigated physiological responses to hypoxia in juvenile flatfishes to determine the implications of hypoxic events in their important nursery habitat in Elkhorn Slough. She presented this research at the SACNAS National Diversity in STEM conference, the Western Society of Naturalists Annual Meeting (where she was awarded “Best Graduate Poster”), and the Ocean Sciences Meeting, in addition to presenting this research in the inaugural “Grad Slam” (3-minute thesis) competition at CSUMB, where she won first place. 

Juliana worked as a teaching associate at CSUMB during her first year of graduate school, before beginning a position as a program assistant for the Coastal and Marine Ecosystems Program (CMEP) at CSUMB. In that role, Juliana helps plan, run, and evaluate all of the educational programs within CMEP, including the Research Experience for Undergraduates (REU) program and the annual Sea Lion Bowl. She also works as a naturalist on a whale watching boat in Moss Landing. When not working, Juliana enjoys spending time with her pets, hiking, photography, and art - mostly watercolor painting and digital illustration. Following graduation, Juliana will be starting an Alaska Sea Grant State Fellowship at the Alaska Fisheries Science Center.

Thesis Abstract:

Estuaries serve numerous important ecosystem roles, including providing critical nursery habitat for juvenile fish. However, due to eutrophication and climate change, estuaries experience highly variable dissolved oxygen (DO) levels and hypoxic conditions. Though hypoxia negatively impacts juvenile fish, there are physiological compensatory mechanisms fish utilize to prevent tissue-level hypoxia. This study examines the effects of hypoxia on two ecologically and economically important flatfish species in Elkhorn Slough on California’s central coast: juvenile English sole, Parophrys vetulus, and juvenile speckled sanddabs, Citharichthys stigmaeus. I measured metabolic rate, ventilation rate, and hematocrit, as well as biochemical indicators of hypoxia (HIF-1a and L-lactate) and oxidative stress (superoxide dismutase), following an acute, six-hour exposure to six DO levels ranging from ambient to severely hypoxic: 8.0, 6.0, 4.0, 3.0, 2.0, and 1.5 mg/L O2. I found that both standard metabolic rate (SMR) and maximum metabolic rate (MMR) in English sole decreased as DO level decreased. A more significant change in MMR compared to SMR also led to a significant decrease in aerobic scope (the ability to increase metabolic rate over resting levels) with decreasing DO levels. For both species, ventilation rate increased as DO level decreased, likely as a mechanism to increase oxygen supply. Both species also exhibited a significant increase in anaerobic activity (increased lactate in muscle tissue) at low DO levels (1.5 mg/L O2 for English sole and 2.0 mg/L O2 for speckled sanddabs). English sole also experienced a significant increase in oxidative stress (as measured by SOD in gill tissue) at 1.5 mg/L O2. Overall, all of these factors can lead to or indicate decreased survival and fitness of juvenile flatfish in hypoxic conditions, with decreased survival potentially reducing population size and fishery success. Evaluating thresholds for tolerance of hypoxia may allow us to predict these changes, as well as determine areas of suitable nursery habitat and targets for estuarine restoration. Since many responses to hypoxia were only observed only at very low DO levels (i.e., 2.0 or 1.5 mg/L O2), these flatfish species appear to have a higher tolerance for hypoxic conditions than other teleost fishes and may be able to withstand many of the environmental hypoxia events observed in Elkhorn Slough, as long as DO levels do not drop below lethal thresholds. Species-specific differences were also found. For two metrics measured, ventilation rate and L-lactate, speckled sanddabs exhibit a nonlinear response, with highest values at mid DO levels, in contrast to a more linear response for English sole, with highest values at low DO levels, suggesting responses to hypoxia may be employed at different DO thresholds for the two species. Additionally, an oxidative stress response was only present in English sole, and not in speckled sanddabs, potentially indicating that speckled sanddabs are better able to withstand hypoxic conditions compared to English sole. If English sole are less tolerant of hypoxic conditions, suitable nursery habitat for this species could be reduced more significantly than for speckled sanddabs, potentially altering the relative distribution and abundance of the two species. 

Juliana Cornett Presents: Physiological Responses to Hypoxia in Juvenile Flatfishes