History of recurrent short and long-term coral bleaching events in Indian coral reefs: a systematic review of contrasting bleaching patterns, lessons learned, and future directions

Climate change has intensified coral bleaching events, leading to widespread coral mortality and threatening the coral reef survival worldwide. However, species susceptibility patterns to bleaching differ spatially and temporally, making it crucial to understand bleaching impact and species susceptibility patterns across latitudinal ranges, particularly from understudied locations. We critically reviewed 23 years of bleaching episodes on Indian coral reefs (four major reefs and other patch reefs) reported from 1998 to 2020 to understand the geographical footprint of bleaching patterns, species susceptibility differences, and their impact. We found that all four major Indian reef systems (Gulf of Kachchh, Gulf of Mannar, Lakshadweep, and the Andaman Islands) have experienced three major bleaching episodes (1998, 2010, and 2016) and multiple short-term bleaching events. Short-term bleaching events (DHWs> four weeks) created differences in species susceptibility, but the disparity among species diminished to long-term bleaching events (DHWs <4 weeks) in all reef sites. Acropora, Porites, Pocillopora, Montipora, and Turninaria in the Gulf of Mannar, Porites, and Favia in the Gulf of Kachchh, and Acropora in the Andaman and Lakshadweep were the most vulnerable genera during all the bleaching events. In terms of recovery, Porites and other massive forms recovered better than branching forms. Furthermore, species susceptibility pattern analysis (winners vs. losers) to 2016 long-term bleaching events found conflicting results from studies (one-time surveys) in the same area. This result indicates that a one-time survey (survey timing) influences results as bleaching events lengthen, necessitating repeated surveys to determine winners and losers. Although inconsistent data from different study sites makes it difficult to create predictive models, data collected over the past 23 years provides critical insight into coral community susceptibility patterns and bleaching impacts, underscoring the need for systematic, uniform surveys in the future.