Solitons mitigate coral bleaching: the Porites perspective

The symbiosis of tropical corals with unicellular dinoflagellates is very sensitive to thermal stress. Even slightly enhanced temperatures can disrupt the tight association and lead to the expulsion of the zooxanthellae. The Andaman Sea coral reefs experienced an especially extensive bleaching event in 2010. Temperature exceeded the bleaching threshold of 30.1 °C by the end of March with peak values around 32 °C by the end of May extending down to 30 m depth. The temperature anomaly caused a complete whitening and high mortality in many of the reefs. However, we found spatial differences in bleaching and recovery related to frequent aperiodic upwelling of cold deep waters entrained by large amplitude internal waves (solitons) likely alleviating the heat stress for the corals. Here, we present data on coral tissue parameters of the massive coral Porites lutea collected along the soliton-exposed west and sheltered east sides of the Similan Islands, Andaman Sea, during samplings prior to, during and after the thermal anomaly, and relate bleaching onset to recovery to concomitant temperature recordings indicating soliton impact. Our data indicate that soliton-exposed corals are likely to be more resilient to bleaching than corals from sheltered areas, and indicate soliton-exposed reefs as potential refuges for corals from mass bleaching.