Thesis Defenses

Thesis Defense by Stephen Pang-April 12th

Mina Sattari

The effect of sex ratio on the reproductive biology of two sex changing fish (Lythrypnus dalli and Rhinogobiops nicholsii)

A Thesis Defense by Stephen Pang

The Ichthyology Lab

Friday, April 12th, 2019 at 12 pm

MLML Seminar Room

Stephen Pang is a master's student under Dr. Scott Hamilton in the Ichthyology Lab. He graduated from the University of Washington in 2012 with a B.S. in biological oceanography. Prior to starting at Moss Landing Marine Labs, Stephen worked in Idaho and central Washington doing salmonid research. He recently completed the Sea Grant State Fellowship (where he was placed with the Delta Stewardship Council in Sacramento) and has recently joined an environmental consulting firm where he continues his work with salmonids and conservation.

Thesis Abstract:

By targeting the largest individuals in a population, size-selective fisheries can influence the life history traits and population parameters of exploited fish stocks. For protogynous (female-to-male) hermaphrodites, this type of harvest is also sex-selective since it preferentially removes males from the population. These differences in sex-specific survival can lead to populations that are heavily female-biased. While males historically have not been considered a limiting factor when assessing the health of gonochoristic populations, modeling work suggests that reduced male abundance and skewed sex ratios could cause a concomitant decline in the reproductive output of protogynous hermaphrodite populations. This study used two nest-brooding sex-changers, Lythrypnus dalli and Rhinogobiops nicholsii, to examine the effect of operational sex ratio on reproductive and nesting success, growth, and rates of sex change. Fish were outplanted on artificial patch reefs at varying sex ratios and their reproductive output was monitored by photographing eggs laid in artificial nests. Sex ratios ranged from 1:1 to 1:19 male:female. Fish were tagged so that growth and sex change could be determined upon recollection from the artificial reefs. For both L. dalli and R. nicholsii, total egg production, female per capita production, average production per nest, and the number of nests per reef were not affected by sex ratio. By contrast, male per capita production and the percentage of nesting males significantly increased as sex ratios became more female-biased. For R. nicholsii, growth rates were highest for individuals that completed sex change during the experimental period. During the breeding season, the frequency of sex change for R. nicholsii was highest on reefs that were strongly female-biased; there was no effect of sex ratio on the frequency of sex change during the non-breeding season. In L. dalli and R. nicholsii, it appears that males do not limit the reproductive output of heavily female-biased populations—as had been predicted by previous modeling work. Instead, for species that defend demersal nests, intrasexual competition between males (i.e., territory and mate monopolization) or females (i.e. competition for nest space) may limit total production when operational sex ratios are more balanced or more female-biased, respectively. As sex ratios became skewed in favor of females, male-male competition was relaxed and individual males became more reproductively successful; the discrepancy in per capita production between males and females at skewed sex ratios indicates that some females would increase their reproductive success by undergoing sex reversal (as demonstrated by R. nicholsii during the breeding season). It is possible that many of the results on reproductive success from this study are specific to nest-brooding species; this highlights the importance of mating systems and reproductive behavior when considering the impact of fisheries on the population dynamics of exploited populations.

Thesis Defense by Alex Olson – December 3rd, 2018

Kimberly Elson

The Biogeochemical Behavior and Speciation of Mercury in the Sea Surface Microlayer:

Implications for Transport to Watersheds via Fog

A Thesis Defense by Alex Olson

Chemical Oceanography Lab

Monday, December 3rd, 2018 at 10am

MLML Seminar Room

Since graduating from CSU Monterey Bay in 2010 with a B.S. in Marine and Coastal Ecology, Alex has worked as a research diver (UCSC, UCSB), fisheries observer (NOAA) and charter boat captain. As a graduate student in the Chemical Oceanography Lab under Kenneth Coale (now Max Grand), his interests center on mechanisms potentially responsible for the transfer of mono-methylmercury in the surface ocean to coastal marine fog. Specifically, he is studying the thin (100 microns) skin layer of the sea surface, building and tuning equipment to collect and eventually analyze material from this layer in the coastal zone. As a student assistant he worked with MLML's Marine Operations Facility, helping maintain the lab's fleet of small research vessels. Alex also assisted in coastal air-sea interaction studies with the Naval Postgraduate School's (NPS) Meteorology Department, first as a MLML student and currently as an employee. 

Thesis Abstract:

Neurotoxic monomethylmercury (MMHg) found in coastal Central California marine advective fog is thought to be a source of elevated MMHg levels throughout the terrestrial coastal foodweb. While not currently present at hazardous concentrations for human exposure directly (17-54 pM), MMHg in fog along the coast poses potential health and ecosystem threats via food-web bioaccumulation and biomagnification processes. The likely marine source and the mechanism of its transport remain unknown. While 2014 vertical profiles from coastal California show surface waters (<6 m) relatively deplete in MMHg (25-185 fM), similar to other ocean basin , surface grab sampling revealed elevated concentrations of MMHg in the uppermost (top ~100mm) portion of the water column known as the surface microlayer (SML). When corrected for dilution during sampling, this could represent a SML concentration of MMHg as high as 1.3 nM, orders of magnitude greater than the localized seawater and fog water; as well as the first such known measurements. Further refined sampling in 2015 of nearshore and offshore waters of California and Oregon supported 2014 findings, with underlying bulk water and SML concentrations from 16 - 380 fM and 4 – 48 fM respectively (Enrichment factors (EF) of 2.5 – 30) These are the first such measurements of MMHg in the SML to our knowledge. SML concentrations were highly variable, likely due to the variable and patchy nature of the SML and its constituents. This may also account for little variability among different surface areas of glass sampling methods. While not statistically significant, these EFs trend with certain oceanographic conditions (temperature, solar radiation, and fluorescence [Chl-a proxy]) suggesting photodegradation and or photodemethylation as major factors affecting enrichment. Although limited, bubble induced SML sea spray aerosol (SSA) production, and thus the ejection of MMHg into the atmosphere as fog nuclei, was also shown to be a potential contributing mechanism to MMHg in fog. Incubation experiments of acidified bulk seawater points to acidolysis of gaseous Dimethylmercury (DMHg) into MMHg as the major pathway of MMHg into regional marine advective fog. Continued comprehensive monitoring via California coastal fog sampling sites (FogNet) and coastal marine features and processes are needed to establish and discern changes in spatio-temporal patterns of the MMHg marine-terrestrial flux.

Thesis Defense by Laurel Lam – December 4th, 2018

Kimberly Elson

Geographic and habitat-based variation in Lingcod (Ophiodon elongatus) demography and life history along the U.S. West Coast

A Thesis Defense by Laurel Lam

Ichthyology Lab

Tuesday, December 4th, 2018 at 12pm

MLML Seminar Room

Laurel is a Master's student under Dr. Scott Hamilton in the Ichthyology Lab. She graduated from UC Santa Barbara with a B.S. in Aquatic Biology and spent several years working for the CA Department of Fish and Wildlife and the Aquarium of the Bay in San Francisco before starting her master's at MLML. Laurel came into the master's program with an interest in fish population biology and working with local fishing communities, so studying Lingcod life-history along the U.S West Coast seemed like the perfect thesis project for her. Throughout her master's career, Laurel has worked closely with state and federal fisheries agencies and has volunteered on several annual research cruises conducted by the NOAA Northwest Fisheries Science Center. In addition, she assisted with conducting entrainment and impingement surveys at the Moss Landing Power Plant with Tenera Environmental and currently works with the Marine Pollution Studies Lab as part of the Bioaccumulation Oversight Group, which investigates harmful levels of organic and man-made contaminates in recreationally caught sportfish in California.

Thesis Abstract:

Fish populations are known to exhibit spatial variability in life history demography due to factors such as temperature, productivity, habitat, and fishing pressure. However, most stock assessment methods neglect to account for these differences and assume that life history traits are constant and unchanging across space and time. As a result, stocks are managed across broad geographic areas with catch quotas, size limits and other regulations applying equally in all places, running the risk of over- or under-harvesting on a regional scale. In this study, Lingcod (Ophiodon elongatus) were collected throughout their U.S. range from 7 geographically distinct areas (Alaska to Southern California) and two habitat types (high-relief versus low-relief) in collaboration with volunteer anglers, recreational party boats, and the federal West Coast Groundfish Bottom Trawl Survey. I evaluated and compared regional and habitat-based differences in Lingcod size and age structure, growth parameters, timing at 50% maturity, total mortality rates and condition indices. Size structure, growth, and maturity rates were found to exhibit a latitudinal cline, where Lingcod in northern waters grew faster and larger, matured at larger sizes than Lingcod in southern waters. There was no latitudinal trend in total mortality, however, Lingcod from Southern California and Washington had the highest total mortality rates compared to all other regions. Between habitats, Lingcod from rocky high-relief habitats grew faster and larger, matured at smaller sizes, and had higher total mortality than fish from trawlable, low-relief habitats. Condition differences were not significant between habitats and did not follow a latitudinal trend, however Lingcod in the Southern California region were in the best condition. Overall, these findings demonstrate significant latitudinal and habitat-based variability in life history and demography of the West Coast Lingcod stock. Differences in growth, maturity, and condition appear to be strongly linked to coastwide patterns seen in sea surface temperature and productivity, while differences in total mortality and demography seem to be influenced by historic and current fishing pressure.

Thesis Defense by Jen Chiu – August 17th, 2018

Kimberly Elson

Diets and stable isotope signatures of Yellowtail Rockfish (Sebastes flavidus) in central California

A Thesis Defense by Jen Chiu

Fisheries & Conservation Biology Lab

Friday, August 17th, 2018 at 12pm

MLML Seminar Room

Jen Chiu is a Master’s student under Dr. Rick Starr in the Fisheries and Conservation Biology Lab.  She graduated from the University of California, Santa Barbara with a B.S. in Ecology and Evolution and a minor in Asian American Studies.  During her time at UCSB, she assisted with research focusing on the non-consumptive effects of predators on prey in the intertidal zone, coupled with the effects of climate change and habitat complexity.  Prior to beginning her graduate work at MLML, she assisted with fisheries ecology research in the Gulf of Mexico, as well as studied the distribution and biomass of benthic invertebrates in the San Francisco Bay.  In addition to her conducting her thesis work, Jen has been a part of the California Collaborative Fisheries Research Program (CCFRP) throughout her entire time at MLML.  She currently serves as the Lead Field Scientist for MLML and the Statewide Coordinator for the program, where she is responsible for managing the MPA monitoring efforts of all academic partners across the state.  She plans to continue her involvement with CCFRP after her defense.

Thesis Abstract:

Studies of fish diets can be used to improve the understanding of feeding habits, trophic distributions, and the predatory role of a species in an ecosystem.  Identifying the spatial and temporal variability in the diets of fishes can provide useful information for stock assessments and fisheries management. Yellowtail Rockfish (Sebastes flavidus) are an important part of the U.S. west-coast commercial groundfish fishery, and abundant along the central California coast.  The most recent studies of Yellowtail Rockfish diets occurred over 20 years ago and originated primarily from studies in Oregon and Washington.  To provide more current information on trophic ecology from California, I examined the food habits of Yellowtail Rockfish collected near Cordell Bank, the Farallon Islands, and Half Moon Bay in 2013 and 2014 using gut content and stable isotope analyses. Yellowtail Rockfish analyzed in this study were semi-pelagic predators, feeding primarily on tunicates, crustaceans, and teleosts.  Based on δ15N values, fish caught in 2013, on average, were feeding at lower trophic levels than those caught in 2014.  δ13C values indicated that fish caught at the northern-most sites were feeding on more pelagic-influenced carbon sources, while those caught at the southern-most sites were feeding on more benthic-influenced carbon sources.  Yellowtail Rockfish in central California can be described as opportunistic feeders because predation patterns were temporally localized, and diets consisted mostly of transitory prey sources.  The Yellowtail Rockfish diet information presented in this study fills data gaps of a key life history component, and will be useful for future stock assessments.

Watch Jen Chiu’s Thesis Defense below:

Thesis Defense by Natalie Yingling – July 20th, 2018

Kimberly Elson

ATP as a Quantitative Proxy for Living Microbial Biomass: Cellular ATP Content Under Stress

A Thesis Defense by Natalie Yingling

Biological Oceanography Lab

Friday, July 20th, 2018 at 4pm

MLML Seminar Room

Natalie Yingling is a Master’s student under the guidance of Dr. Nick Welschmeyer in the Biological Oceanography lab. She started at MLML in Fall 2015 after earning her B.S. degree in Marine Science with a concentration in biological oceanography from North Carolina State University in Spring 2015. During her time at MLML she has participated in various research cruises, worked as a research assistant for Dr. Welschmeyer as part of the ballast water testing team that works in conjunction with Cal Maritime, was vice president of MLML in 2016 and has participated every year in MLML’s annual open house. In Fall 2018 she will be starting a Ph.D. program at Florida State University in the department of Earth, Ocean and Atmospheric Science. Her thesis focuses on implementing measurements of adenosine triphosphate as a proxy of microbial biomass in stressed and dying cells.

Thesis Defense by Tyler Barnes – June 21st, 2018

Kimberly Elson

Assessing beach variability & shoreline change in Monterey Bay, CA

A Thesis Defense by Tyler Barnes

Geological Oceanography Lab

Thursday, June 21st, 2018 at 12pm

MLML Seminar Room

Tyler Barnes is a graduate student in the Geological Oceanography Lab at MLML. His curiosity in in coastal processes was sparked as an undergraduate at the University of San Diego where he joined a research lab investigating sedimentation in bays with coral reefs in St. John, USVI. Soon after, Tyler began his master’s degree in which his research assesses geomorphologic change on beaches in Monterey Bay using a terrestrial laser scanner (ground-based LiDAR that creates 3-D models of surveyed surfaces). Simultaneously, Tyler has worked as a researcher for Central Coast Wetlands Group where he has assisted on projects monitoring bar-built estuary hydrology/ecology throughout California and completed topographic surveys for restoration projects.

Watch Tyler Barnes’s Thesis Defense below:

Thesis Defense by Catarina Pien – June 29th, 2018

Kimberly Elson

Changes in the elasmobranch assemblage in a California estuary

A Thesis Defense by Catarina Pien

Pacific Shark Research Center

Friday, June 29th, 2018 at 12pm

MLML Seminar Room

Catarina Pien is a Master's student under Dr. David Ebert in the Pacific Shark Research Lab. She received her B.A. in Biological Sciences from Wellesley College, where she spent some time abroad in the Caribbean studying mangroves and their associated species assemblages. After coming to the Moss Landing Marine Laboratories, Catarina continued to work in estuarine systems, focusing her work on the life history and ecology of shark and ray species in Elkhorn Slough. While at MLML, Catarina worked as museum curator for several years, getting to know the many interesting organisms collected and donated over the years, as well as for Tenera Environmental, and the California Department of Fish and Wildlife. She recently started as a Sea Grant State Fellow for the Delta Stewardship Council in Sacramento, where she is helping review science and adaptive management in the Sacramento-San Joaquin Delta. 

 

Thesis Abstract:

Elkhorn Slough is an estuarine system that provides habitat for several elasmobranch species. During the past century, the hydrography and habitat of Elkhorn Slough have dramatically changed. Previous studies suggest shifts in the species composition and habitat usage patterns of elasmobranchs. This study characterizes the elasmobranch species composition, and examines the environmental conditions associated with differences in distribution by sex and life stage. Elasmobranchs were sampled from 2015 –2016 by longline and gillnet. Bat rays (Myliobatis californicus), leopard sharks (Triakis semifasciata), and thornback rays (Platyrhinoidis triseriata) were most commonly observed, and were generally more abundant during the dry seasons and in the mid-slough, where environmental conditions were more similar to those in Monterey Bay. Differences in distribution by sex and life stage were associated with season, zone, and associated environmental variables including temperature and salinity. Historical analyses indicate that changes in the assemblage occurred over decadal time scales, associated with increases in mudflat habitat and large-scale climatic shifts (i.e., Pacific Decadal Oscillation), indicating that both habitat and climatic changes may continue to influence the estuarine assemblage in the future.

Watch Catarina Pien’s Thesis Defense below:

Thesis Defense by Evan Mattiasen – June 6th, 2018

Kimberly Elson

Effects Of Hypoxia on the behavior and physiology of juvenile state temperate reef fishes (genus: Sebastes)

A Thesis Defense by Evan Mattiasen

Ichthyology Lab

Wednesday, June 6th, 2018 at 4pm

MLML Seminar Room

Thesis Abstract:

The progression of climate change is predicted to cause large-scale changes to ocean chemistry (i.e., shifts in temperatures, salinity, ocean acidification, etc.) within the California Current. Forecasts from climate models and oceanographic observations indicate an increase in the frequency and duration of hypoxic events in the coastal zone, which have the potential to affect marine biodiversity and fisheries. Many studies have shown that exposure to extreme low dissolved oxygen (pO2) conditions can have deleterious effects on fish in early life stages, such as inhibition to growth and reproduction. Rockfish (Sebastes spp.) are a diverse group of species composed of fishes with varying life history characteristics. This study aims to determine how exposure of two species of young-of-the-year (YOY) juvenile rockfishes will perform under chronic exposure to varying dissolved oxygen levels. Copper rockfish (Sebastes caurinus) and Blue rockfish (Sebastes mystinus) are two closely related species that differ in early life history traits. Copper rockfish have a short pelagic duration that begins with parturition in the spring and ends with recruitment to the kelp forest canopy after 1-2 months. Blue rockfish have a longer pelagic duration that begins in the winter and ends with recruitment to the benthic kelp forest habitat after 3-6 months. I compared how behavior and physiology were affected under chronic exposure to low pO2 at four treatment levels (ambient = 9.0 mg O2 L-1, moderate = 6.0 mg O2 L-1, low = 4.0 mg O2 L-1, hypoxic = 2.0 mg O2 L-1). Behavioral tests were aimed at identifying changes in exploratory behavior (i.e., escape response trial), predator detection through olfactory perception (i.e., olfactory choice test), and changes in turning preference (i.e., behavioral lateralization). Physiological tests focused on determining changes in hypoxia tolerance (critical oxygen tension, pCrit), the capacity for aerobic activity (i.e., aerobic scope), and ventilation rates. Changes in growth rates of both species were also measured. The findings of this study indicate that both species express sensitivity to low pO2; however, the strength of the response differed between species. Copper rockfish exhibited decreased growth rates and reduced absolute lateralization following chronic exposure to the lowest oxygen levels. Behavioral tests did not differ with treatment for blue rockfish. Additionally, growth rates for Blue rockfish followed the opposite trend of Copper rockfish where individuals in the lowest oxygen treatment grew more than those in the control treatment. Both species exhibited decreases in aerobic scope and increases in ventilation rates with decreasing oxygen levels. Copper rockfish had a lower tolerance of hypoxia and weaker acclimation response compared to Blue rockfish as measured by critical oxygen tension threshold (pCrit). A lower pCrit for fish exposed to low oxygen conditions indicates the potential for acclimation to those conditions. Despite the physiological changes that occurred for both species in low oxygen conditions, these results provide evidence of acclimation to chronic hypoxia. Species with a greater capacity for acclimatization are potentially those with life history characteristics where larvae/juveniles have a higher probability of exposure to low oxygen conditions, leading to either acclimatization in the field or pre-adaptation to hypoxia over multiple generations. The differences expressed by each species suggest that acclimatization to changing ocean conditions may vary across closely related species, leading to winners and losers under future ocean conditions. Overall, increases in strength and frequency of coastal hypoxia events may have severe impacts on juvenile stage rockfishes that reside in kelp forests. While this study highlights adaptations to low oxygen, extended exposure to hypoxia decreased fitness of individuals through metabolic and aerobic depression, and changes to behavior. The information gathered in this study is critical for advancing the understanding of how these economically valuable species will fair in the future, and the information presented here will help inform policy makers to protect populations at risk.

Watch Evan Mattiasen’s Thesis Defense below:

Thesis Defense By Cody Dawson – May 7th, 2018

Kimberly Elson

Phenology and the Response to Disturbance of the fucoid, Stephanocystis osmundacea

A Thesis Defense by Cody Dawson

Phycology Lab

Monday, May 7th, 2018 at 4pm

MLML Seminar Room

Cody Dawson is a Master's student in the Phycology Lab under the expert tutelage of Mike Graham. He received his BS in Biology from Humboldt State University where he was mainly working with invertebrates and predator-prey dynamics. Upon joining MLML in 2014, he discovered a love for seaweed which led him to a project surrounding their physiology that would become his life for the next 3 years. With the completion of his MS, he will be moving onto to study the trophic ecology of nearshore ecosystems in the Alaskan Beaufort Sea at the University of Texas at Austin as a part of his PhD.

Thesis Abstract:

Nearshore rocky ecosystems along exposed shorelines experience frequent disturbances due to turbulent swells and wave action. These disturbances directly affect subtidal algal communities that provide biogenic habitat along the coast. This habitat shapes faunal communities by providing refuge through structural complexity. In central California, kelps are the most notable providers of biogenic habitat, but, seasonally, a prolific fucoid, Stephanocystis osmundacea, adds a considerable amount of habitat into the environment. While diminutive and bushy during the winter, this alga produces canopy-forming reproductive fronds during the spring and summer months that add to the biogenic refuge. The purpose behind this study was to understand how the frequency and timing of disturbances affect the physiology of Stephanocystis. This was accomplished by performing manipulations on the reproductive and vegetative tissues of the alga, including: full reproductive removal (-R), haphazard vegetative blade damage (-V), no removal (C), and damage of both reproductive and vegetative structures (-All). Using measurements of changes in total length (cm) as a proxy for biomass allowed for an in situ assessment of the response by the alga. This external response measurement was coupled with stable isotope analysis of internal response using carbon and nitrogen as a bioindication of fitness. Removal of reproductive fronds during spring elicited a dormancy response, while damage to the vegetative tissue reduced growth, possibly by limiting overall photosynthetic capacity. These results suggest that spring frond growth is important to reproductive fitness and removal can stimulate a life history trade-off between reproduction and survival. Winter manipulations elicited no response due to the dormancy period of this species. Enrichment values for ∂C and ∂N were consistent with reported values for other brown algal species but, because of the timing of extraction, the internal chemistry of the individuals rebounded and the ability to detect a response was lost. Both the natural and manipulated populations had similar ∂C and ∂N when separated by tissue and time of year, which indicates that while the alga may be impacted from an external perspective, it will recover internally and stay as a viable part of the reproductive population. Understanding how these seaweeds respond to biomass loss provides a better perspective of disturbance effects on this species and the ecosystem it helps support.