My work focuses on connecting ocean conditions to the behavior and success of marine mammal populations. 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 marine predator species, primarily pinnipeds, on topics ranging from cellular-level physiology to species-level behavior and ecology.
Current Projects
Pinnipeds as Ocean Observers
Advancing technology has enabled researchers to collect more and more in situ environmental data concurrent with behavioral observations. We use high-resolution temperature, salinity, light level, fluorescence, and dissolved oxygen data to better describe the physical characteristics of utilized habitat and directly relate environment to foraging behavior.
Extent and Magnitude of Subsurface Anomalies During the Northeast Pacific Blob as Measured by Animal-Borne Sensors.
Holser, R.R., T.R. Keates, D.P. Costa, C.A. Edwards. (2022) J. Geophys. Res.: Oceans. DOI: 10.1029/2021JC018356
Chlorophyll fluorescence as measured in situ by animal-borne instruments in the northeast Pacific Ocean. Keates TR, RM Kudela, RR Holser, LA Hückstädt, SE Simmons, DP Costa. 2020. Journal of Marine Systems, 203, 103265.
Niche Partitioning – Ross Sea, Antarctica
A collaboration between researchers at the University of Canterbury and the Costa Lab at UC Santa Cruz. We’re working to assess how three co-occurring marine predator species, Weddell seals, Adelie penguins, and emperor penguins, partition foraging resources in the Ross Sea. We completed our first field season deploying instruments at Cape Crozier in November 2024.
Sea Lion Behavioral Response Study
The soundscape that marine animals experience while at sea can profoundly affect their physiology and behavior. Using new and developing tracking technologies, we will observe how individual California sea lions in the Southern California Bight respond to naval sonar. These movement data will then inform energetic models to assess population-level consequences of their response to this acoustic disturbance.
Sea Level Rise and Pinniped Haulout Habitat
Using monthly drone imagery of haulout sites along the Central California coast, we are assessing how the terrestrial habitat of pinniped species may decrease or shift based on predicted sea level rise over the next several decades. Pinnipeds are dependent on terrestrial habitat for reproduction, molting, and as a refuge from marine predators.
Effects of Multiple Stressors
Northern elephant seals are a model system for assessing stressors in deep-diving marine mammals. I am part of a large collaborative effort with researchers from UC Santa Cruz, USGS, Sonoma State University, and Moss Landing Marine Labs to experimentally assess the interactions between contaminant load, acoustic disturbance, and varying environmental conditions on northern elephant seal foraging and reproductive success.
Multiple stressors interact in a free-ranging marine mammal: mercury bioaccumulation and cortisol influence endocrine and immune biomarkers. Peterson, S.E., J.T. Ackerman, R.R. Holser, B.I. McDonald, D.P. Costa, D.E. Crocker. 2023. Environmental Science and Technology
Adrenal response to ACTH challenge alters thyroid and immune function and varies with body reserves in molting adult female northern elephant seals.
Northey, A., R.R. Holser, G. Shipway, D.P. Costa, D.E. Crocker (2023) AJP Regulatory Integrative and Comparative Physiology. DOI: 10.1152/ajpregu.00277.2022