Investigating coral reef response to extreme heating events, along The Chagos-Laccadive Ridge, across a gradient of human pressure.

Nairika Bharucha

The most prominent threat to coral reefs worldwide is thermal anomalies, like the ENSO, that lead to coral bleaching. Coral reefs are also under serious threat from human-induced environmental and local stressors. The Chagos-Laccadive Ridge is an underwater ridge in the Indian Ocean, consisting of three island groups – Lakshadweep, Maldives and Chagos. The human pressure across the three island groups varies widely.

 The main aim of this project is to examine the impact on reef health and coral composition caused by the 2016 ENSO, across this human pressure gradient. Live coral cover (LLC) has been used as a proxy for reef health and DHW for heat stress, while population density and distance from the closest inhabited island are proxy for human pressure.

We saw significant differences in the benthic composition and LLC before and after the 2016 ENSO. We also found patterns that suggested that sites closer to human inhabited islands showed larger decline in LLC than sites further away. Thermal anomalies also caused a change in coral genera composition, drastically reducing the percentage coral cover of heat-sensitive branching genera, such as Acropora and Poccilopora, and slightly increasing the percentage coral cover of more heat-tolerant genera, such as Porites.