Bleaching in the Andaman Sea: potential mitigation mechanisms

The Andaman Sea experienced extensive coral bleaching events in the years 1991, 1995 and 2003 but showed no significant mortality during these events. In 2010 an extremely severe bleaching event was monitored on several reefs along an offshore cross-shelf island gradient and data revealed up to 100% bleached coral colonies during the peak temperature phase, yet with some reefs showing considerably lower bleaching intensities. Even, ten months after the peak temperature stress most of the reefs appeared stressed starting slowly to recover, with again some reefs recovering faster. Additionally, environmental parameters as temperature and sedimentation rate were measured. A characteristic of the region is the existence of large amplitude internal waves (solitons) approaching the islands from the west, which introduces pulses of cold, nutrient-rich and turbid water into the shallow reef areas. High-resolution temperature records displayed that these phenomena prevailed during the temperature rise and served as cold showers during temperature highs. The current Andaman Sea bleaching monitoring showed the importance of fully capturing the environmental background especially underwater temperature regime and how it influences coral reef ecosystems. However, factors such as species composition, sedimentation, and biological invaders can additionally positively or negatively impact reefs during bleaching events and make predictions even more complex. Regions with reoccurring temperature anomalies providing cold water pulses could be important for coral reef recovery to serve as refuges replenishing adjacent severely damaged reefs with new recruits. The knowledge of such environmental variability is an important requisite to predict the severity of bleaching events.