Dominic McAfee, Melanie J. Bishop , Nina T. N. Yu and Gray A. Williams
Climate warming is challenging the survival of animals, particularly in environments that are already hot. To avoid the potentially lethal temperatures experienced on hot, sunny days, many animals shelter in habitats that are cooler and less stressful than their surrounds. As temperatures continue to warm globally, the availability of these cooler habitats may determine whether animals survive or go extinct. On shorelines around the world, the shells of oysters growing close together provide shade from the sun and trap water when the tide goes out. Oysters may provide cool shelters that protect shoreline animals and plants from climate warming, but their efficacy in doing so may depend on how flat or erect they sit on the rock. We need to know which growth forms we should encourage to provide the best protection. In an aquarium experiment, we compared how single oysters and oysters that grow flat or erect in groups modify the temperatures experienced on bare rock. Under present-day summer high temperatures there was little difference in the cool shelters provided by flat and erect groups of oyster, each of which provided cooler and moister conditions than single oysters or bare rock. Under elevated temperatures, however, the erect oysters provided substantially cooler and moister conditions than the flat oysters, which no longer supported cooler shelters. At elevated temperatures, animals (sea snails and chitons) that shelter amongst oysters experienced less stress (elevated heart rates) when associated with erect than flat oysters. This suggests that as the climate gets hotter, the ability of oysters to provide a cool shelter to associated animals will be dependent on their maintenance of an erect growth form. This knowledge will help inform conservation projects aimed at reducing the impacts of climate warming on coastal animals.