Bleaching impacts on carbonate production in the Chagos Archipelago: influence of functional coral groups on carbonate budget trajectories

Abstract

Reefs in the remote Chagos Archipelago (central Indian Ocean) were severely affected by sea-surface temperature warming and coral bleaching in 2015-2016. Here we assess the impacts of this event on community composition and reef carbonate production at twelve fore reefs sites across three atolls. Bleaching caused a 69% decline in coral cover, mostly driven by mortality of tabular Acropora spp., and a 77% decline in mean coral carbonate production (2015: 13.1±4.8; 2018: 3.0±1.2 kg CaCO3 m2 yr-1). Changes were accompanied by a major shift from competitive to stress-tolerant coral taxa, with magnitudes of decline comparable to those reported elsewhere in the Indian Ocean, despite inter-site differences in dominant coral species. These trends differ from those on reefs dominated by stress-tolerant taxa, which experienced minor declines in production post-warming. The study highlights the potential for different suites of functional coral groups to drive divergent post-bleaching budget responses.