The 2014 thermal stress event on offshore archipelagoes in the South China Sea

Abstract

Episodes of coral bleaching and subsequent mortality due to abnormal ocean warming have happened more frequently in the world's tropical seas. In 2014, a significant level of thermal stress event was predicted by NOAA CRW in the South China Sea(SCS). In this paper, we estimated the thermal stress anomaly and severity based on NOAA CRW HotSpot and Degree Heating Weeks (DHW) products. An ecological survey was also conducted on nine reefs of Xisha Islands in the SCS from June 2 to June 6, where coral reefs suffered serious damage due to the crown-of-thorns starfish outbreaks in 2007. Satellite results suggest that the beginning of thermal stress in 2014 in the SCS was in mid-May while the ending was in mid-September. Satellite seawater temperature anomalies of +1–2.5°C were recorded at a number of locations. Except the southern portion of Nansha Islands, four offshore archipelagoes tend to be all influenced by this significant warming event. At the time of survey, no significant warming event in Xisha Islands was predicted by NOAA CRW, but scattered coral bleaching was found on Yinyu. Besides, coral cover index of scleractinians indicates obvious coral recovery in Xisha Islands since 2007. The effects of thermal stress in 2014 on coral reefs in the SCS deserve to pay attention and need further investigation.