How do you Know if a Coral Reef is Growing or Shrinking?

Here is her report from a wet and windy Indian Ocean: Professor Chris Perry and I are studying the carbonate budgets of coral reefs around the islands of the Chagos Archipelago. Chris has developed the “Reef Budget” method that we use to calculate how much carbonate is produced by coral and calcifying algae, and how much is eroded by grazers such as sea urchins and fish, as well as by internal bioerosion from boring worms and microorganisms. The results provide a metric on reef “health” informing on its growth or erosion.

The reefs in Salomon and Peros Banhos atoll that we have visited so far have displayed a massive decline in coral cover due to severe bleaching in 2016, which resulted in carbonate production rates dropping to one third of 2015 values. Nonetheless, many Porites and some Acropora colonies survived the bleaching event, and there are large numbers of small recruits of different species. We found many live encrusting coral, especially in the understory of reef structure. Thanks to the abundance of herbivorous fish, the substrate is clean from macroalgae. Calcareous algae that cover the dead coral substrate continue to produce a significant amount of carbonate, which “glue” the reef structure together and provide a great substrate to recruit more coral. We therefore hope that the once glorious coral reefs will recover quickly in the coming years.