What was linked to a faster reef recovery after coral bleaching?

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Coral bleaching and the resulting changes in seabed communities and population size structure can weaken reef functions, including providing habitat and producing carbonate that supports reef growth. The net reef carbonate budget—the balance between carbonate production and erosion—is an important indicator of reef health.

Researchers quantified changes in coral community composition, colony size structures and the resulting carbonate budget trajectories after the 2015/2016 bleaching event in the remote Chagos Archipelago in the Indian Ocean. They conducted ReefBudget surveys at 12 sites across three atolls in 2015, 2018 and 2021, using locally obtained calcification and bioerosion rates to calculate biological carbonate production and erosion.

Following bleaching-driven mass coral mortality, budgets shifted from net positive in 2015 (mean ± SD: 3.8 ± 2.6 G) to net negative in 2018 (−2.4 ± 1.4 G), where G = kg CaCO3 m−2 yr−1. By 2021, all sites were on a recovery trajectory, but net budgets differed significantly between atolls, ranging from −2.0 ± 1.7 to 2.2 ± 1.4 G.

At Salomon atoll, threefold faster recovery of carbonate production and a return to positive reef budgets just 6 years after bleaching were associated with the persistence of high structural complexity and the rapid recovery of fast-growing tabular Acropora spp. Differences in colony size distributions between atolls indicated that coral identity and size class are more important predictors of reef functions and post-disturbance recovery speed than coral cover alone.