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Topic

Heat, food availability and habitat degradation: How environmental conditions shape the resilience and physiological responses of marine invertebrates across scales

Department of Biology

Date & location

• Wednesday, December 17, 2025
• 12:00 P.M.
• Clearihue Building, Room B007

Examining Committee

Supervisory Committee

• Dr. Amanda Bates, Department of Biology, ӣ��Ӱ�� (Supervisor)
• Dr. Rana El-Sabaawi, Department of Bology, UVic (Member)
• Dr. Alyssa Gehman, Marine Biologist, Hakai Institute (Outside Member)
• Dr. Jon Lefcheck, Center for Environmental Science, University of Maryland (Outside Member)

External Examiner

• Dr. Christian Nozais, Département de biologie, chimie et géographie, Université du Québec à Rimouski

Chair of Oral Examination

• Dr. Jason Fisher, School of Earth and Ocean Sciences, UVic

Abstract

Increases in ocean temperature are having large-scale impacts globally on marine communities. Elevated temperatures surpassing thermal optima for organisms directly affect their survival. However, access to food and habitat quality can buffer the negative effects of increased ocean temperatures by providing energy and refugia for communities. As metabolic rates increase with rising temperatures, organisms require more food to meet their energetic needs, and without access to sufficient food, they may not survive. Additionally, an organism's access to food is influenced by the condition of its habitat. As habitats become more degraded, they provide less complexity for organisms to live and grow in, thereby reducing the availability of resources. Together, the direct and indirect effects of environmental conditions influence the resilience and physiological responses of marine invertebrates across multiple biological scales. At an ecosystem scale, I investigate the direct effects of local temperature refugia and kelp forests on the resilience of marine invertebrates during marine heatwaves. I show that cooler refugia sites experienced more abrupt increases in species density, though these species were primarily warm-affinity urchins. These changes highlight the importance of examining species-specific responses to changes in temperature and habitat conditions in improving our understanding of how invertebrates within these ecosystems respond to environmental change. Then, at a community scale, I examine how temperature-dependent consumption rates of fish affect predation pressure on marine invertebrates across Eastern Australia. These results demonstrate how the indirect effects of temperature on fish metabolism influence marine invertebrate distributions and highlight potential vulnerabilities during marine heatwaves. Finally, at the species scale, I conducted two experiments with the sea star Dermasterias imbricata to investigate the role of food in mitigating the negative effects of temperature on sea star behaviour and physiology. Without access to food, I show that sea stars under thermal stress are energy-limited and must reallocate energy to processes necessary for survival, and away from processes required for immune defence, growth, and reproduction. Combined, these investigations across three scales provide valuable knowledge that will inform how marine invertebrate communities and their ecosystems may change as global climate change continues.