Coral bleaching and recovery in the Thai Andaman Sea

Severe coral bleaching in response to increasing sea temperatures threatens coral reefs in many regions of the world, including the Andaman Sea, Thailand. Coral bleaching involves the breakdown of the coral-algae symbiosis, resulting in the loss of the intracellular microalgal dinoflagellates of the diverse genus Symbiodinium, also called a zooxanthellaea . Elevated temperatures and high solar irradiation are considered to be the primary factors causing widespread coral bleaching. In the Andaman Sea, bleaching events have occurred in the years 1991, 1995, 1998, 2003, 2010, and 2016 following abnormally high sea-surface temperatures (SST). The 2010 SST anomaly was the hottest on record with unprecedented bleaching and mortality of corals. However, corals showed different responses to thermal stress and important spatial differences, both between and within reefs. This thesis explores the causes and consequences of coral bleaching events in the Andaman Sea of Thailand on the coral community, organismal and sub-organismal (symbiont) scale. Physico-chemical factors as well as species-specific responses of corals to thermal stress contribute to complex patterns of bleaching and mortality, revealing large differences in acclimatization and adaptation in space and time. Understanding the species-specific bleaching responses in their particular environment provides a promising tool for management, as the identification of bleaching-tolerant corals and the factors enhancing coral tolerance may help improve the design of appropriate rehabilitation techniques. This study highlights potential refuge areas for corals which are necessary to protect and facilitate quick post-bleaching recovery. The protection of reef areas harbouring coral communities tolerant to thermal stress, along with the rehabilitation of degraded coral reef ecosystems with bleaching tolerant species, is a promising approach to improve the success of reef conservation management in a warming ocean.