Thesis Defense by Isaak Haberman – December 8

"Drivers of intertidal purple sea urchin (Strongylocentrotus purpuratus) reproductive capacity and the implications for kelp forest recovery"
A Thesis Defense by Isaak Haberman

Invertebrate Ecology Lab

| Live-Stream | December 8th, 2023 at 3:00 pm PDT


Kelp forests are integrally important ecosystems along eastern Pacific coastlines, sequestering carbon, reducing wave erosion, and increasing biodiversity in coastal marine communities. However, kelp forest coverage in central California has experienced major decline in the past decade, being replaced with unproductive urchin barren habitats. The factors affecting the establishment and persistence of urchin barrens have been extensively researched in the subtidal, but the influence of intertidal sea urchin populations is unknown. Moreover, intertidal populations are likely connected to subtidal communities via larval dispersal, so an understanding of intertidal urchin reproductive dynamics is important. I collected urchins and biological and environmental data from nine sites along the Monterey Peninsula in central California with varying algal communities, urchin densities, and wave exposures. I weighed and extracted the gonads from urchins at each site to measure gonadal somatic index (GSI%), a representation of reproductive capacity proportional to urchin size. I found that intertidal urchin reproductive capacity is unrelated to coralline algae cover or urchin density; contrary to what is seen in the subtidal. There is a weak positive relationship between fleshy algae coverage and reproductive capacity. Moreover, urchins collected from sites that had higher drift algae presence exhibited higher reproductive capacities. This indicates that urchins in the intertidal are resilient to poor fleshy algae coverage where they are living because drift algae is continually deposited into intertidal environments for them to consume. Therefore, the intertidal can support higher densities of healthy sea urchins that may represent an important contribution of urchin larval supply to subtidal urchin barrens. Kelp restoration efforts must be amended to include intertidal areas - especially those of high urchin densities - in order to maximize their efficacy.



I am a graduate student at CSUMB and MLML advised by Alison Haupt and co-advised by Amanda Kahn. I completed my undergraduate degree at the University of British Columbia where I studied marine biology and did research on the caloric value of different seaweed species. My thesis at CSUMB focuses on the reproductive capacities of intertidal populations of purple sea urchins (Strongylocentrotus purpuratus) and how these populations are important to consider for kelp forest restoration techniques. My research interests are nearshore community ecology, applied ecology, and generally how species interactions and habitat shape the species composition of different nearshore areas. After I graduate, I will be teaching at CSUMB in the spring. In my spare time I like doing crossword puzzles, going camping and climbing, and watching the Packers.

Thesis Defense by Melissa Palmisciano – December 8th

"Assessing the effects of upwelling-driven pH and dissolved oxygen variability on juvenile rockfishes"
A Thesis Defense by Melissa Palmisciano

Ichthyology Lab

Zoom | December 8th, 2023 at 10 am PDT


Global climate change is expected to increase the frequency and severity of upwelling events in the California Current Ecosystem, yielding concurrent reductions in pH and dissolved oxygen (DO) in coastal marine environments. Juvenile copper (Sebastes caurinus) and gopher (S. carnatus) rockfish may be particularly vulnerable to low pH and DO because they settle nearshore during the upwelling season. To determine how fluctuations in ocean chemistry impact rockfish behavioral and physiological performance at this critical life history stage, I exposed juveniles of both species to one of the following pH/DO treatments: periodic upwelling (a recurring cycle of 8 days of 7.3 pH, 2.0 mg/L DO, followed by 8 days of recovery at control conditions), extreme static (7.3 pH, 2.0 mg/L DO), moderate static (7.5 pH, 4.0 mg/L DO), or control static (8.0 pH, 8.3 mg/L DO). Responses to sublethal stress were evaluated through behavioral metrics including lateralization, escape time, and startle response, as well as physiological metrics including critical swimming speed (Ucrit), metabolic performance (standard and maximum metabolic rates, capacity for aerobic activity), hypoxia tolerance (critical oxygen tension [Pcrit]), growth rates, body condition, and mortality. I did not observe any significant effects of low pH/DO conditions on the behavioral metrics, but physiological performance generally decreased as pH/DO decreased. In the fluctuating treatment, both species were impaired under upwelling but often appeared to recover in the physiological metrics when returned to control seawater for 6-7 days (a simulated oceanographic relaxation event). Both species exhibited the lowest growth rate in the extreme low pH/DO treatment, followed by the fluctuating treatments and then the moderate treatment, suggesting that fluctuations had an overall negative effect compared to constant mean conditions. While juvenile rockfish are susceptible to physiological impairment under extreme climate change scenarios, the severity and duration of future hypoxic, acidic events will ultimately set the consequences for survivorship and physiological fitness, influencing the outcome of the population replenishment process and the long-term sustainability of economically and ecologically important nearshore rockfish species.



Melissa graduated from Brown University in 2013 with an Sc.B. in Environmental Science. As an undergraduate, Melissa studied spatial and temporal distributions of macroalgae blooms in relation to nutrient loading for her senior thesis. At Moss Landing, Melissa joined the Ichthyology Lab and was advised by Scott Hamilton, studying the effects of climate change stressors like hypoxia and ocean acidification on the behavior and physiology of juvenile rockfishes. She was also involved in a project looking at the effects of climate stressors on larval rockfishes. During her time at MLML, Melissa served as a leadership committee member for the Monterey Bay Chapter of the Society for Women in Marine Science. Melissa is now pursuing her PhD at Hopkins Marine Station exploring how ocean acidification impacts grazer-algal interactions and community structure in the Mediterranean. In her free time Melissa enjoys hiking, gardening, and traveling.