Specific Thermal Regime and Coral Bleaching Pattern in Hengam Island, the Eastern Persian Gulf

Thermal anomaly is among factors initiating coral bleaching and mortalities and threatening coral reefs worldwide. Therefore, susceptibility of corals to thermal stress is a central concern in reef conservation. In this study, we evaluated underwater temperature during 2012-13 and bleaching status of corals during summer 2012 in Hengam Island located in the eastern Persian Gulf. Hengam coral community - faced with milder seasonal temperatures compared with more inward coral communities of the Persian Gulf – usually experiences substantial mitigation of underwater temperature (i.e. ~1-5°C) during high-tides in the warm season. In August 2012, some corals of Hengam community including species from the families Faviidae, Pocilloporidae, Poritidae and genus Coscinaria, Psammocora, Turbinaria, Montipora and Symphyllia bleached after ~3 weeks of exposure to daily average underwater temperature >33°C. Therefore, bleaching threshold (BT) of the corals was ~2°C lower than BT of southeastern counterparts. Acropora downingi, the dominant coral with high live coverage was not affected by the bleaching. This contradicts the usual bleaching pattern observed in the Persian Gulf, in which acroporids were the most extensively damaged coral or among the bleached ones. Based on results, it is postulated that bleaching of Acropora is slowed down by the fast tidal flows and rapid cooling in Hengam, a promising event for times of increasing temperature.