Data - Reef community productivity and calcification – spatial and temporal variability in recovering coral reefs

Coral reef Net Community Production (NCP) and Net Community Calcification (NCC) are measures of the functioning of reef ecosystems, currently under threat due to multiple anthropogenic stressors. We assessed these rates using a benthic gradient-flux approach (BEAMS system) on forereef and lagoon coral reefs that were recovering from the major 2015-2016 bleaching event in the Chagos Archipelago, Indian Ocean. Structure-from-Motion (SfM) Photogrammetry from 2019-2022 indicates significant recovery, with an increase of ~60% in hard coral cover and ~10% in rugosity between 3 to 6 years post-bleaching. Biogeochemical measurements show net heterotrophy at both reefs 3 years within the recovery, with the lagoon reef exhibiting in particular high rates. Six years into the recovery process, productivity and calcification rates at the forereef more than doubled compared with the rates 3 years prior, while calcification rates computed from SfM increased by 34%. Large day-to-day variability was documented. This included a transition in the lagoon reef from net calcification to dissolution within days, despite the long-term trend of net CaCO3 accumulation. On the forereef, an increase of 51% in heterotrophy was measured on cloudy days, while a shift to autotrophy (147% increase in NCP) and 47% higher calcification were found on sunny days that directly followed cloudy days. An internal wave event presumably led to enhanced production on one of the days on the forereef. Our findings highlight the importance of combining long-term reef health indicators with short-term measurements of reef functioning for a comprehensive understanding of reef responses to environmental changes.