Ambientes com maior variação de temperatura selecionam corais mais resistentes ao estresse térmico?

Abstract

Climate change have been increasing the frequency and severity of coral bleaching events, contributing to coral mass mortality and reef degradation. However, corals can have different susceptibilities to bleaching and distinct abilities to recover after stress events, as some corals have bleached less and survived more under thermal anomalies. This pattern might be related to the natural temperature variability in their origin sites, which may prompt different mechanisms for corals to cope with thermal stress, through adaptation or acclimatization to local conditions. We conducted laboratory and field experiments with Siderastrea stellata colonies from habitats with high (tide pools), medium (shallow reef; 2m) and low temperature variability (deep reef; 28m). In the laboratory, we evaluated corals from different origins and their response to thermal stress, accessing photosynthetic efficiency and color change. In the field, we investigated coral capacity to acclimatize to different environments through a reciprocal transplant experiment, comparing corals from environments with different temperature dynamics. Tide pool corals bleached less and did not suffer great decrease in photosynthetic efficiency when exposed to thermal stress, whereas corals from more thermally stable environments (shallow and deep) showed higher vulnerability to bleaching and underwent alarming decrease in photosynthetic efficiency. Deep reef corals also bleached and suffered reduction in photosynthetic efficiency when they were transplanted to reefs with more prominent temperature variation. Our results revealed that tide pool corals are more resistant than corals from shallow and deep reefs, suggesting that high temperature variability favors tolerance mechanisms that enable corals permanence in these thermally variable sites, while making them more prepared to deal with climate change.