Seminar – Oceanographic Measurements of a Marine Heatwave and the Behavioral Response of a Top Predator: The Northeast Pacific Blob 2014-2017

Dr. Rachel Holser, University of California: Santa Cruz
Presenting: "Oceanographic Measurements of a Marine Heatwave and the Behavioral Response of a Top Predator: The Northeast Pacific Blob 2014-2017"

MLML Seminar | November 16th, 2023 at 4pm

Watch the Live Stream here or here


All organisms face resource limitations that will ultimately restrict population growth, but the controlling mechanisms vary across ecosystems, taxa, and reproductive strategies. As climate change continues to alter ecosystem processes across the globe, organisms are confronted with new challenges to their ability to survive. The Northeast Pacific Blob was a multi-year marine heatwave that affected ecosystems across the Northeast Pacific, from producers to top predators. We quantified the subsurface extent and evolution of the Blob using oceanographic instruments carried by northern elephant seals (Mirounga angustirostris), a top predator that forages on the abundant biomass of the mesopelagic Northeast Pacific Ocean. We then assessed the effect of this marine heatwave on the foraging behavior of adult female northern elephant seals. We used a combination of telemetry data collected by instrumented seals (temperature, salinity, location, depth) along with body composition and energy gain metrics to examine the population-level effects of the Blob. We found significant warm anomalies throughout the top 1000m of the water column during the Blob, and that northward advection of warm, salty water at the base of the pycnocline likely played an important role in the sustained accumulation of warm water. Comparing foraging behavior during 2014 and 2015 to our 15-year tracking time series, we found evidence of a plastic behavioral response.  Females increased their use of the Alaska Gyre, increased their daytime foraging effort, and increase their use of deep water (>800m depth) during the summer months, suggesting that the prey field changed relative to previous years. Northern elephant seals are both generalist predators and capital breeders, which may buffer the effect of acute events, allowing them to adjust to environmental variability more than highly specialized or constrained predator species. Biologging technology not only increases our understanding of animal behavior, but also gives us unprecedented insight into the changing environment these animals are experiencing.


I am an Assistant Researcher with the Institute of Marine Sciences at the University of California, Santa Cruz. I study the behavior and ecology of marine mammals and how it relates to oceanographic processes.  My work to date has primarily focused on a major marine heatwave in the North Pacific and its effects on the reproduction and foraging ecology of the northern elephant seal.  I am particularly interested in individual variability in behavior, what drives and maintains that variability, and what the ecological consequences are for a population. I have had the privilege and opportunity to work with several different pinniped species, from Antarctica to the Bering Sea, on topics ranging from cellular-level physiology to species-level behavior and ecology.  Currently, I am part of a collaborative effort to assess the consequences of multiple stressors on northern elephant seals.  We are evaluating the interacting effects of acoustic disturbance, contaminant load, varying foraging conditions, and acute physiological stress responses on reproductive success.

Thesis Defense by Alex Lapides – Nov. 27

"The Feeding Habits and Selectivity of Siphonophores in Monterey Bay"
A Thesis Defense by Alex Lapides

Invertebrate Ecology Lab

Zoom | Live-Stream | November 27th, 2023 at 12:00 pm PDT

Alex Lapides sorts trawl remnants on a R/V Western Flyer cruise with the Monterey Bay Aquarium Research Institute


Gelatinous zooplankton are historically understudied and we have much to learn about how they fit into the larger food web.  Of gelatinous zooplankton, siphonophores are especially known to have broad diets and to select for a wide variety of prey.  In this study we investigated siphonophore feeding habits using a long-term remotely operated vehicle video dataset from the Monterey Bay, CA.  In addition, we quantified the degree of specialization for each siphonophore-prey pair, and we investigated the relationship between genetic distance and specialization differences.  We found siphonophores tended to belong to one feeding guild and in some cases fed exclusively on one prey.  Siphonophores also selected strongly for a few specific prey.  We found a slight relationship between genetic distance and siphonophore specialization.  Overall, this study upholds previously known trends about siphonophore diet, selectivity, and phylogenetic patterns and expands our knowledge of the midwater food web.



Alex received her B.S. in Ecology and Evolution from UC Santa Cruz in 2018 before coming to MLML in the Fall of 2020.    She has held a variety of technician positions ranging from research vessel operations to molecular lab work to machine learning, and has studied a variety of habitats ranging from salt marshes to the deep sea.  Overall, she is most interested in problems concerning the open ocean that leverage large datasets and statistics to make inferences about the environment, and is most content behind a computer playing in R.  In her free time, Alex likes to perform aerial silks, spin fire, and play Magic: the Gathering

The siphonophore Nanomia bijuga, one of the most common in Monterey Bay and a major player in midwater food webs

The siphonophore Praya dubia is one of the ocean's longest animals. It eats gelatinous prey as well as krill.

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.

Thesis Defense by Kameron Strickland

"Habitat-mediated efficacy of 360 degree diver-operated video for quantitative surveys of California reef fishes"
A Thesis Defense by Kameron Strickland

Ichthyology Lab

Zoom | Live-Stream | November 13th, 2023 at 3:00 pm PDT


Temperate rocky reefs feature a mosaic of complex macrohabitat features which host a variety of demersal fish species. Giant kelp forests add considerable vertical structure to rocky reefs, including macrohabitats extending from the reef to the upper water column. Much of what we know about temperate communities derives from shallow SCUBA surveys in which divers record observations using underwater visual census (UVC) techniques. Increasingly, these communities are being studied with video techniques first utilized in deeper water. While UVC provides immediate data on fish communities and requires no additional technology either for data collection or post-processing, imagery captures the fine-scale associations between fish specific habitat features that elude UVC techniques. While traditional video cameras constrain the field of view available to a UVC diver, 360˚ cameras record everything in all directions, eliminating the need to selectively survey one direction underwater. However, questions remain as to how data derived from 360˚ video transects compare to the more well-established UVC transects, particularly in complex environments. My primary research objective was to examine the trade-offs associated with 360˚ video and UVC when quantifying attributes of the demersal fish community across multiple sites and macrohabitat types. I performed SCUBA dives at four sites around the Monterey Peninsula in central California. Pairing UVC and 360˚ video, I recorded fish counts along 30 meter demersal transects. Richness, diversity, abundance, and density of fishes from UVC and 360˚ video were compared statistically with two-way analysis of variance (ANOVA) and non-metric multidimensional scaling (NMDS). Results indicate that within fish-habitat guilds, counts of species were similar between methods at all macrohabitats and most sites. 360˚ video and UVC produced similar results with respect to species richness and diversity. Differences between the methods arose by looking at density at any scale, as well as total count per meter of all fishes. These results suggest that with some caveats, 360˚ video transects can be incorporated into temperate subtidal reef monitoring without compromising data quality.



Kameron graduated with his B.S. in Marine Science from CSU Monterey Bay in 2019. There, he was heavily involved in the SCUBA program, both volunteering for courses and diving for his personal capstone project. Early discussion of Kameron's thesis project was already in progress when he joined the Ichthyology lab in 2020. After learning to create 360˚ video SCUBA dives, Kameron wanted to put the technology through trials and see how 360˚ video transects surveyed kelp forest fish compared to SCUBA divers. During his time at MLML Kameron performed video analysis for the Fisheries and Conservation Biology Lab's BOSS video lander project at San Clemente Island, became a SCUBA Instructor, started a marine consulting job, and even worked as a long-term substitute teacher across multiple grade levels. In his free time, Kameron enjoys wildlife photography and can be found taking cameras precariously close to seawater.

Kameron immediately after finishing his first drysuit dive in Monterey

Kameron and team at CSUMB deployed benthic video landers from Morro Bay to Half Moon Bay to study the abundance of fishes inside and outside of MPAs

Thesis Defense by Ryan Chiu

"Spatiotemporal Dynamics and Biogeochemical Responses in a Tidally Restricted Moro Cojo Slough"
A Thesis Defense by Ryan Chiu

Physical Oceanography Lab

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


Four years of observational data for Moro Cojo Slough (MCS), a Mediterranean climate estuary in central California, linked anthropogenic nutrient loading and hydrological modifications to a shift in net ecosystem metabolism (NEM) that differs from the characteristic net heterotrophic behavior of most estuarine systems. A lack of precipitation and limited flushing during the dry seasons, as evidenced from hypersaline waters, contribute to high ecosystem respiration rates that drove NEM to nearly balanced or net autotrophic. During the wet seasons, increased runoff and nutrient loading due to precipitation elevated primary production rates within MCS, characterizing the system as net autotrophic. Box models developed for the estuary determined that: 1) salinity was primarily controlled by advection and runoff, 2) high nitrate fluxes were advected into the slough at the mouth, and 3) the processes that dominate DO fluxes were biological processes and gas exchange. Field deployments of DO loggers further reinforced this dependence on daytime primary production and nighttime ecosystem respiration, as observed in the diurnal variabilities in DO. With anthropogenic factors playing a critical role in MCS’s net autotrophic characterization, there is concern that heavily modified systems may begin to exhibit a shift in metabolic behavior and ultimately act as a net source of carbon.