Upcoming Thesis Defenses

Thesis Defense by Shelby Penn – May 9th

Olivia Beaudoin

"Comparing mercury accumulation and the macroalgal microbiome between coastal and estuarine populations of sea lettuce (Ulva spp.)"

A Thesis Defense by Shelby Penn

MLML Phycology

Live-Stream | May 9th, 2025 at 10:30 am PDT

ABSTRACT

Mercury is a potent neurotoxin that bioaccumulates and biomagnifies in marine environments. Most research on mercury cycling in the ocean focuses on pelagic food webs, leaving a gap in knowledge regarding macroalgal-based food webs. Seaweed from the genus Ulva is globally distributed in marine and brackish habitats, accumulating metals and toxins with minimal impact on the host. While the mechanisms behind Ulva’s tolerance to marine pollution are unclear, studies suggest that the macroalgal microbiome may play a crucial role. This study investigates how collection location influences mercury uptake and bacterial community composition in Ulva. Estuarine and coastal Ulva were subjected to 1, 50, and 200 ng/L of mercury in 6-day laboratory experiments. Total mercury concentrations were measured using a Direct Mercury Analyzer-80, while the Ulva microbiome's taxonomic composition was estimated from the V3-V4 regions of the 16s rDNA gene. Results indicated that estuarine samples accumulated higher mercury concentrations than coastal samples (PERMANOVA, p < 0.001). The microbial community structure differed between coastal and estuarine Ulva samples (PERMANOVA, p = 0.1) at various taxonomic levels. Differential abundance analysis revealed that 81 operational taxonomic units (OTUs) from 8 classes were enriched in coastal Ulva, while 147 OTUs from 12 classes were enriched in estuarine Ulva. This study demonstrates that the Ulva microbiome and mercury uptake are influenced by habitat. Additionally, the microbiome differences due to habitat may affect mercury uptake. Although the microbiome of Ulva in estuarine environments potentially enhances the macroalgal holobiont's resilience to nutrient and toxin loads, host health must also be considered given the toxicity of mercury and the lower accumulation observed in coastal Ulva populations.

BIO

Originally from Virginia, Shelby earned a B.S. from Allegheny College in 2013. During her undergraduate studies, she spent a semester abroad in Bonaire, Dutch Caribbean, where she studied marine ecology and conservation and became certified as a Scientific Diver. While there, she conducted a SCUBA-based research project on the behavior of diseased ocean surgeonfish. She also completed internships at MarineLab in Key Largo, FL, and at the National Aquarium. Her senior thesis focused on the feeding morphologies of two species of darter fish.

Before beginning her graduate studies at Moss Landing Marine Laboratories (MLML), Shelby worked as a marine science instructor, Divemaster, and expedition guide on Catalina Island, in Hawaii, and throughout Southeast Alaska. She joined the Phycology Lab at MLML in 2018, where her master's research focused on the role of the Ulva microbiome in the cycling of mercury in coastal ecosystems. Her initial research interests centered on how mercury and other metals enter coastal food webs, and the role macroalgae play in their bioaccumulation and biomagnification. Through this work, she developed a passion for seaweed-associated microbial communities and will continue her studies as a Ph.D. student, investigating the direct and indirect effects of the marine environment on foundational seaweed holobionts.

While at MLML, Shelby also served as a Monterey Area Research Institutes’ Network for Education (MARINE) Liaison and Society for Women in Marine Science (SWMS) Mentor, participated in Skype a Scientist, contributed to rhodolith research projects on Catalina Island and served as Assistant Dive Safety Officer, supporting a variety of field-based research efforts.

Thesis Defense by Travis Leggett – May 8th

Olivia Beaudoin

"Advancing Benthic Survey Methods: A Novel Application of Diver-Operated Stereo Video to Survey the Influence of Benthic Habitat Variation on Urchin and Macroalgae Populations in California Rocky Reefs"

A Thesis Defense by Travis Leggett

MLML Invertebrate Ecology

Live-Stream | May 8th, 2025 at 2:00 pm PDT

Abstract
Subtidal surveys are critical for ecosystem monitoring, traditionally involving diver underwater visual census (UVC), though such methods can impose time or logistical restrictions on the study. Imagery-based techniques, such as diver-operated stereo-video (stereo-DOV), offer precise 3-dimensional measurements from 2-dimensional images, facilitating accurate size and distance estimates as well as the ability to survey large areas quickly. This study compared two stereo-DOV angles (45° and 90°) with UVC to estimate benthic macroinvertebrates, macroalgae, and habitat characteristics (relief, substrate, benthic cover) within kelp forests and urchin barrens. We also explored associations between habitat complexity, measured as relief and substrate transitions. Stereo-DOV and UVC surveys yielded similar estimates for species richness, diversity, and purple sea urchin (Strongylocentrotus purpuratus) densities in urchin barrens, and for stipitate algae species. However, algae significantly reduced the effectiveness of both stereo-DOV angles compared to UVC, largely driven by the absence of cryptic species in stereo surveys. The 90° stereo-DOV surveys performed better in kelp forests relative to 45° surveys but still measured lower species richness and diversity compared to UVC surveys. Habitat characterization accuracy was similar between methods, though these similarities occurred mainly for broad substrate categories (e.g., sand, bedrock) and intermediate relief sizes (>10 cm - <1 m). Habitats with relief transitions (>1 per 10m²) showed marginal positive correlations with giant kelp (Macrocystis pyrifera) and negative correlations with purple urchin densities. Substrate transitions positively correlated with stipitate algae density. Our findings suggest stereo-DOV may be suitable for monitoring community-scale changes in urchin barrens with reduced performance in kelp forests. The 90°Stereo-DOVsurvey estimates were more similar to UVC estimates than 45° stereo-DOV surveys, but habitat was a more significant influence on stereo-DOV performance. This study provides insight into using stereo-DOV as a benthic surveying tool in kelp forests and urchin barrens and the potential for habitat transitions to support kelp populations while limiting urchin movement.

Bio

Travis earned a B.S. in Marine Science from CSUMB after transferring from Santa Monica City College. At CSUMB, Travis was introduced to scientific applications for SCUBA diving and began on a career path that would keep him underwater. During his undergraduate degree, he worked with the Partnership for Interdisciplinary Studies of Coastal Oceans at UCSC with Dr. Mark Carr, where he cemented his passion for subtidal research. He went on to work at Hopkins Marine Station of Stanford University as an independent undergraduate researcher, studying the effects of climate stressors on urchins and other benthic grazers. Travis started his Master's at MLML in 2020 with Dr. James Lindholm, studying the influence of habitat contiguity on urchin populations at Monastery Beach in Carmel Bay. Travis received funding from the Center for Coastal and Marine Ecosystems and the Educational Partnership Program for Minority Serving Institutions through NOAA to expand his research to include a methodological comparison of stereo-video and underwater diver visual surveys. While at MLML, Travis served as the Student Body Treasurer and has certified over 100 individual students for various levels of SCUBA training as an instructor at CSUMB. In his free time, Travis enjoys underwater photography, backpacking, travelling, and spending time with his dog Lehua.

Thesis Defense By Bennett Bugbee – May 8th

Amadeo Scott

"EFFECTS OF DENSITY ON MORPHOMETRICS AND REPRODUCTIVE PHYSIOLOGY IN THE BULL KELP (NEREOCYSTIS LUETKEANA), AN ANNUAL FOUNDATION SPECIES"

A Thesis Defense by Bennett Bugbee

MLML Phycology

Live-Stream | May 8th, 2025 at 9:00 am PDT

Bennett holding a crowned bull kelp from the Albion soral bank tank at the MLML shore lab.

Abstract

The bull kelp, Nereocystis luetkeana, is the predominant canopy forming kelp along much of the northeastern Pacific. However, it remains largely understudied due to the dynamic nature of its niche coupled with its annual life history. For populations to persist, reproductive sporophytes must release substantial spores to facilitate successful sexual fertilization among male and female gametophytes that will develop into the next cohort of sporophytes. High densities of spores increases the likelihood of completing the alternation of generation life cycle characteristic of kelp genera. Yet those high densities of spores have the potential to result in a high density of sporophytes, competing for light to reach the surface canopy. It is currently unknown how density-dependence will alter the morphological development and reproductive investment of Nereocystis, thereby affecting population persistence. To address this, I investigated how density affects the morphology and reproductive traits of Nereocystis across its life history. Laboratory studies were conducted to test the effects of density on gametogenesis, gametophyte growth, female egg production, and sporophyte production. Additional studies were conducted on juvenile whole sporophytes and crowned sporophytes (i.e., modified to retain a small portion of the pneumatocyst) in land-based tumble culture to assess the effects of density on survivorship, stipe growth, pneumatocyst growth, blade growth, blade development (number), and reproductive investment (soral number, blades bearing sori, and soral size). Low spore density treatments resulted in significantly larger female gametophytes. Intermediate spore densities yielded higher eggs per female, yet there were no significant differences across density treatments. Sporophyte density was significantly greater at higher spore densities. Juvenile sporophytes grown in tumble culture showed no significant difference in survivorship as a function of sporophyte density. High densities delayed sporophyte development compared to sporophytes grown in low density treatments, which were characterized by long stipes and numerous blades. Density-dependent effects on crowned sporophytes were similar to juvenile sporophytes with low densities promoting increased growth and development, while high densities inhibited normal development. At 4 weeks, sporophytes shifted from allocating resources from growth to reproduction. Soral (i.e., reproductive tissue) size and soral number exhibited a significant negative density-dependent relationship. At the individual scale, low density treatments displayed significantly greater reproductive investment. However, scaling reproduction to the population resulted in intermediate densities having the highest cumulative reproductive potential. Given its life history and need for sustained annual reproductive success to fuel population replenishment, these results suggest that Nereocystis may have a higher threshold for negative density-dependent interactions compared to other perennial kelps.

 

Bio

Bennett earned his B.S. in Biology from Pacific Lutheran University in 2018. While at PLU, when not competing on the men’s soccer team, he developed his passion for marine environment and got SCUBA certified. After joining the Phycology lab at MLML, he quickly began spending a lot of time in the water, helping fellow students collect data, developing ideas for his thesis, and working on bull kelp restoration projects in Mendocino and Sonoma counties. Much of his research focused on bull kelp morphometrics and physiology, both in the lab and in the field. Outside of his research, he served as Open House co-chair, brew club organizer, and a Phycological Society of America Student and Early Career Researcher committee member. He can often be found in the tidepools around the Monterey Peninsula or running around with his dog Scuba. After graduation, Bennett will continue at MLML as a technician on the bull kelp restoration efforts in Mendocino, along with working at Monterey Bay Seaweeds.