Andrew Bickell

Topic

Impacts of Heatwaves and Hypoxia on Gene Expression in the Pacific Oyster and the Development of Monitoring and Mitigation Tools for Summer Mortality

Department of Biology

Date & location

• Friday, May 9, 2025
• 3:00 P.M.
• Virtual Defence

Examining Committee

Supervisory Committee

• Dr. Amanda Bates, Department of Biology, University of Victoria (Co-Supervisor)
• Dr. Chris Pearce, Department of Biology, UVic (Co-Supervisor)
• Dr. Timothy Green, Fisheries and Aquaculture, Vancouver Island University (Outside Member)

External Examiner

• Dr. Bernarda Calla, Agricultural Research Service, US Department of Agriculture

Chair of Oral Examination

• Dr. Marlea Clarke, Department of Political Science, UVic

Abstract

Marine heatwaves and coastal hypoxic events are increasing in frequency and intensity under anthropogenic climate change, resulting in widespread mass mortalities of the Pacific oyster (Crassostrea gigas). Those mortality events threaten the economic stability of global aquaculture, yet strategies to monitor oyster health and mitigate losses during periods of environmental stress are largely limited. Changes in gene expression of C. gigas in response to laboratory-simulated heatwaves and hypoxic events were assessed to identify candidate monitoring genes and explore artificial aeration as a potential mortality mitigation strategy. Two laboratory experiments were performed, exposing farmed C. gigas to simulated 10-day heatwave and hypoxic conditions similar to a 2021 marine heatwave that triggered farmed oyster mortality in Baynes Sound, British Columbia, Canada. Gill tissues were periodically sampled during the experiments and total RNA was extracted to explore patterns of gene expression via RNAseq and qPCR. Five candidate genes were consistently differentially expressed in both experiments— death-associated inhibitor of apoptosis 2 (A2I), high mobility group protein DSP1 (DSP1), high mobility group box 1 (HMGB1), heat shock protein 90 (HSP90), and peptidyl-prolyl cis-trans isomerase (PPCTI)—demonstrating potential for monitoring summer mortality. No significant differences in expression of the general stress marker genes heat shock protein 70 (HSP70) and heat shock protein 20 (HSP20) were detected, suggesting that genes related to immune function and regulation of transcription may be more appropriate for monitoring summer mortality. In addition, the presence of artificial aeration resulted in significantly lower HSP90 relative expression, suggesting some potential utility in stress mitigation during heatwaves. The present work provides insights into the role of heatwaves and hypoxia in Pacific oyster summer mortality and will inform effective monitoring and mitigation practices to support the adaptation of shellfish aquaculture to the growing impacts of climate change.