Gerardo ZARDI

coolOYSTER : microbial symblotic thermal mitigation against heatwaves in oysters

Oyster die-offs induced by Heatwaves (HWs) exemplify the severe economic and ecological effects of extreme heat events. Oysters are among the major aquaculture commodities and dominant ecosystem engineers that support biodiversity and underpin myriad ecosystem functions and services. Given the widespread lethal effects of HWs on oyster populations, the economic repercussions are substantial. In France, the oyster farming industry has been particularly struck by summer mass mortalities of juvenile and adult oysters. Indeed, over the last two decades such episodes have become increasingly more severe and frequent threatening the entire oyster commercial production.

coolOYSTER is inspired by my recent work showing how the large-scale impact of HWs on intertidal mussels can be mitigated by microbial symbionts. Critically, my research on the widespread symbiosis between endolithic microbes and mussels show that endolithic microbes can lower hosts’ body temperatures during HWs, significantly enhancing the probability of survival by up to 50%. This remarkable and vital effect is caused by the whitening of the outer shell layer induced by the endolithic shell boring which increases the reflected component of solar irradiance, subsequently reducing the amount of solar energy absorbed by the shell and, as a result, the organism’s overall body temperature.

Because endolithic microbes are ubiquitous in bivalve shells, the enhanced resistance to intense heat stress they provide to mussels is likely to extend to a variety of intertidal organisms. My preliminary results show significant thermoregulatory effects of endolithinduced shell whitening in oysters. However, we still do not know (i) whether endolithic microbial thermal buffering enhances oyster survival and (ii) to what extent thermal stress mitigation stretches from the individual oyster to the entire ecosystem. Through coolOYSTER, I will apply my current knowledge and acquire new skills to fill this fundamental knowledge gap. I will take a geographically comprehensive, interdisciplinary approach that merges wide-ranging field surveys, pioneering biophysical modelling, ecosystem functions and ecosystem services valuation to take the first step towards the development of a general framework that captures the pivotal role of biological interactions in the context of HWs.