Combined effects of thermal conditions and food availability on thermal tolerance of the marine bivalve, Perna viridis.

Organisms can mitigate the effects of long term variation in environmental conditions through acclimation, which involves changes in various physiological responses. To elucidate the possible effects of temperature and food concentrations on acclimation capacity, physiological responses of the mussel, Perna viridis, were measured after individuals were held for six weeks under varying temperatures and food availability. Warm-acclimated mussels experiencing higher food levels had significantly greater upper thermal limits than those maintained on lower food levels. In contrast, the upper thermal limits of cold-acclimated mussels were not affected by food levels. For warm-acclimated mussels, differences in upper thermal limits were likely due to rapid depletion of energy storage as predicted by Dynamic Energy Budget model simulations for P. viridis exposed to lower food levels. Clearance rates of cold-acclimated mussels were significantly lower than warm-acclimated mussels, regardless of food availability. The impacts of lower food acquisition on energy storage, however, could be compensated by lower metabolic rates of the cold-acclimated mussels. The availability and the ability to acquire food are not, therefore, the main drivers differentiating between the upper thermal tolerances of cold- and warm-acclimated mussels, but these differences are driven by the past thermal history the mussels experienced. The temperature tolerance range of P. viridis showed a positive shift to tolerate higher temperatures after acclimation. Such flexibility in thermal tolerance implies P. viridis has high capacity to acclimate to novel environments, which will enhance its future success given its commercial importance as an aquaculture species.