An Integrated Oceanographic and Physiological Framework for Identifying Climate Refugia for Marine Invertebrates

Climate refugia-areas buffered from environmental change-are increasingly important for marine conservation and fisheries management, yet identifying their location and extent remains challenging. We developed a framework using established ecological and physiological concepts describing temperature-induced stress to map potential thermal refugia-areas expected to be resilient to thermal stress. Our framework uses three complementary approaches to analyze daily temperature records and quantify relative thermal stress across sites. We applied this to economically important green abalone (Haliotis fulgens) along 1200 km of Baja California (Mexico) coastline, in the southern California large marine ecoregion. Using satellite sea surface temperature data from 1186 sites spaced at 1 km intervals along the coastline, converted to bottom water temperature via in situ validation, we calculated relative thermal stress based on: (1) short-term temperature variability, because stress from rapid changes can exceed acclimatization capacity; (2) exposure to thermal extremes, because prolonged heat exposure induces thermal stress; and (3) long-term temperature deviations, because extreme cold and hot conditions may not be optimal for organism performance. Each approach revealed distinct spatial patterns, with relative stress varying substantially from individual bays (< 10 km) to regional gradients (> 500 km). Despite differences, 18% of the coastline (213 of 1186 sites) exhibited consistently low relative stress across all three definitions, concentrated north of 28° N. An additional 28% met low-stress criteria for two definitions, spanning 28° N-32.5° N. To evaluate the robustness, we used 18 years of catch-per-unit-effort fisheries data from Isla Natividad. Exposure to thermal extremes (stress definition 2) best explained abalone catch patterns, accounting for 61% of variance. Results demonstrate that refugia identification depends critically on how thermal stress is defined, yet consensus areas across multiple definitions provide a generalizable framework for identifying robust targets for climate-resilient marine management in an era of accelerating ocean change.