Exploring thermal tolerance across time and space in a tropical bivalve, Pinctada margaritifera

Ectotherm vulnerability to climate change is predicted to increase with temperature variation. Still, translating laboratory observations of organisms’ heat-stress responses to the natural fluctuating environment remains challenging. In this study, we used an integrative framework combining insights from thermal death time (TDT) curves and physiological reaction norms to precisely capture Pinctada margaritifera’s thermal performance and tolerance landscape. We then applied this integrative model to predict individuals’ cumulative heat injury as a function of actual temperature conditions documented at five contrasting islands across French Polynesia. Substantial injury was predicted for spats (ranging from 30.24% to 29.62%) when exposed to eight consecutive extreme low tide events in Nuku Hiva. Overall, this study highlights the potential of this framework to effectively quantify the impact of extreme events, such as marine heatwaves, and to guide resource management initiatives.

Methods
Three different experiments (E1, E2 and E3, details below) were performed using hatchery-produced individuals issued from two reproduction events. The E1 experiment aimed to assess larval development completion (i.e., performance and upper limits) under a wide range of temperatures and intensities (i.e. time of exposure).In turn, the E2 and E3 allowed investigating the thermal sensitivity of spats experiencing stressful and permissive temperatures, respectively.