Aerial exposure tolerance of juvenile flat oysters (Ostrea angasi) depends on shell length and air temperature

Abstract

Oyster reefs have declined globally, impacting ecosystem structure, function, and services. The flat oyster Ostrea angasi was a dominant ecosystem engineer throughout southern Australia, forming extensive reefs now diminished to <1% of historical coverage. Restoration of O. angasi has gained traction over the last decade, exclusively in subtidal habitats. However, O. angasi historically occurred in the intertidal zone, which could broaden restoration opportunities and success. There is little information quantifying factors that influence the performance of O. angasi in intertidal habitats. To test survival of O. angasi under thermal and desiccation stress experienced in intertidal habitats under winter, summer, and heatwave conditions, we emersed individuals from three age classes (1, 4, and 7 months old) at air temperatures of 10, 25, or 40°C in a series of laboratory experiments. Oysters exhibited moderate tolerance to exposure, with survival depending on interactions between emersion duration and temperature, and emersion duration and shell length. Survival broadly increased with shell length, but decreased with temperature and emersion duration. We used model predictions from the laboratory experiments to simulate intertidal survival rates at a potential restoration site in southern Australia. The simulation revealed low survival when low tides coincided with heatwaves. Field validation is needed to understand the effects of repeated tidal cycles and other biotic and abiotic influences. Our findings provide preliminary evidence for extending the restoration range of O. angasi into the low intertidal zone and can be considered when mitigating transport‐related mortality during large‐scale restoration.