Coral bleaching due to increased sea surface temperature in Gulf of Kachchh Region, India, during June 2016

摘要

The 2015-2016 E1 Nino Southern Oscillation event was one of the extreme climate events which elevated the sea surface temperature (SST) of tropical oceans, which in turn increased the level of thermal stress on corals. Coral bleaching event is mainly caused due to high positive SST anomaly, i.e., when SST exceeds its normal summer maxima. Corals in the Gulf of Kachchh region of Gujarat earlier experienced coral bleaching events during 1988, 2010 and 2014. For this study, SST was derived from NOAA OISST data set which is available daily at 0.25 degrees global grids from 1982 to present. The climatologically warmest month for the Gulf of Kachchh region is June when the maximum monthly mean temperature is 29.31 degrees C, as observed from NOAA OISST. The present study focuses on monitoring daily SST anomalies during summer 2016 for the Gulf of Kachchh reefs and field observations on early responses of coral bleaching from Laku Point reef, a site known for high coral diversity. It was found that in summer 2016, SST rose to 30.62 degrees C and recorded a maximum positive anomaly of 1.31 degrees C in the month of June. A total of 72 days out of 122-day monitoring period showed positive SST anomaly, including 28 days of continuous positive thermal stress in June 2016.To validate coral bleaching forecast at the end of the regional warmest quarter, a field visit was carried out at Laku Point reef near Poshitra village in the southern coast of the Gulf of Kachchh. A total of 13 coral species and a sea anemone were found bleached in various proportions during the field sampling after two months of prolonged thermal stress. The field data showed an average of 3.9% bleaching of corals at colony scale. The maximum proportion of colony scale bleaching was observed in Porites lutea species.