Ocean acidification enhances the bioerosion of a common coral reef sponge: implications for the persistence of the Florida Reef Tract

Abstract

The increase in anthropogenic carbon dioxide in seawater, termed ocean acidification (OA), depresses calcification rates of coral and algae, and may contribute toward reef ecosystem degradation. To test how future OA conditions will influence biologically-mediated dissolution (bioerosion) of coral by the common Caribbean boring sponge Pione lampa (de Laubenfels, 1950), we conducted a series of carefully controlled incubations and used changes in total alkalinity (TA) to calculate calcium carbonate dissolution. We present data showing a positive relationship between seawater pCO2 and chemical bioerosion that predict a 99% increase in chemical erosion before the end of the century, more than double the expected decline in coral calcification rate. To examine how OA-enhanced erosion will influence reef ecosystem persistence, we incorporated these and other data into a carbonate budget model of 37 reefs along the Florida Reef Tract (FRT). Our model showed that all FRT reefs had a positive CaCO3 budget [mean = 8.257 (SE 0.8077) kg m-2 yr-1 ] in preindustrial times, whereas approximately 89% of reefs presently exhibit net erosion. Present-day reef-specific calcification would need to increase by 29.4% to compensate for projected end of the century OA-enhancement of total bioerosion. These findings show that OA may accelerate Caribbean and Atlantic coral reef degradation more rapidly than previously predicted.