Shellfish Reefs in Hot Water: A Forecast for a Temperate Estuary in a Climate Change Hotspot

Shellfish reefs are among the most imperiled marine ecosystems, and restoration efforts are increasing worldwide. In the Swan–Canning Estuary (Western Australia), four shellfish reefs were constructed using limestone boulders and seeded with Mytilus galloprovincialis. Survival was lower than expected, potentially reflecting summer water temperatures exceeding its thermal tolerance. To identify shellfish species most likely to persist under present and future conditions (+1 °C), we developed thermal-suitability models combining seasonal temperature profiles with species-specific realized thermal distributions. Sixteen shellfish species were assessed. Species with intermediate thermal optima performed best: Saccostrea glomerata and Trichomya hirsuta remained within their modelled ther-mal-suitability ranges for >95% of the time. In contrast, M. galloprovincialis remained within its modelled thermal-suitability range for 70.8–74.0% of the time under present conditions, and 63.3–65.4% following warming. Cool-affinity species, including Ostrea angasi and Mimachlamys asperrima, were increasingly constrained by high summer temperatures, whereas warm-affinity species, such as Saccostrea cucullata, were limited by low winter temperatures. These results indicate that the persistence and future species composition of shellfish reefs in warming estuaries will depend strongly on their thermal tolerance and highlight the value of incorporating climate projections into restoration planning.