Available at: https://digitalcommons.calpoly.edu/theses/3179
Date of Award
11-2025
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
College
College of Science and Mathematics
Advisor
Kevin Johnson
Advisor Department
Biological Sciences
Advisor College
College of Science and Mathematics
Abstract
Olympia oysters (Ostrea lurida) are the only native oyster species to the North American West Coast. A once thriving species, O. lurida populations have dramatically declined over time due to factors such as overharvesting, habitat degradation, and the introduction of invasive predators. Although their populations are still present in estuaries along their habitat range, many of these same stressors persist today, preventing the re-establishment of dense oyster beds and hindering recovery of populations. Among these current day stressors, a major concern are the impacts of climate change, specifically warming water temperatures and the increased frequency of hypoxic events. As sessile organisms in the low intertidal and shallow subtidal zones, O. lurida are especially vulnerable to the conditions of their variable environment. Two Central California O. lurida populations from Elkhorn Slough and Morro Bay estuaries were identified as high priority sites for O. lurida conservation aquaculture. Future conservation aquaculture strategies may employ crossbreeding of two O. lurida populations to enhance broodstock quality and grow population sizes within each estuary. However, to proceed with this strategy, we must first evaluate potential local adaptations as well as climate change resiliency within each source population. This study set out to explore whether there were differences between the Elkhorn Slough and Morro Bay O. lurida populations when exposed to elevated temperature and low oxygen stress. To explore this, we compared responses of O. lurida from these populations to elevated water temperature (22°C) and anoxia (0 mg O2/L) on survival, enzyme activity of certain biochemical indicators of metabolic strategy [PK:PEPCK activity], oxidative stress response [tAOX], and gene expression patterns. We found significant population differences in survival: Morro Bay O. lurida survived longer than those from Elkhorn Slough under anoxia challenges. Enzyme measurements of PK:PEPCK activity indicated distinct metabolic strategies, with Morro Bay O. lurida maintaining greater reliance on aerobic metabolism, while Elkhorn Slough O. lurida maintained greater reliance on anaerobic metabolism. We did not find significant differences in oxidative stress response by measurement of tAOX. Comparative transcriptomics utilizing differential gene expression analysis found population-specific and shared patterns of transcriptional response to elevated temperature and oxygen limitation challenges. Both populations exhibited mostly shared gene expression patterns suggesting limited evidence for local adaptations to these stress challenges. Weighted gene correlation network analysis emphasized the significant and broad transcriptional responses to oxygen limitation but interestingly not to temperature. These findings suggest that the two populations show limited evidence of divergent local adaptations and physiological responses to elevated temperature and anoxia. Consequently, Elkhorn Slough O. lurida populations may benefit from receiving Morro Bay O. lurida to enhance broodstock quality, providing a practical strategy for their conservation.
Included in
Biology Commons, Cellular and Molecular Physiology Commons, Genetics and Genomics Commons, Marine Biology Commons