Disturbances drive changes in coral community assemblages and coral calcification capacity

Anthropogenic environmental change has increased coral reef disturbance regimes in recent decades, altering the structure and function of many coral reefs globally. In this study, we used coral community survey data collected from 1996 to 2015 to evaluate coral calcification capacity (CCC) dynamics with respect to recorded pulse disturbances for 121 reef sites in the Main Hawaiian Islands and Mo'orea (French Polynesia) in the Pacific and the Florida Keys Reef Tract and St. John (U.S. Virgin Islands) in the Western Atlantic. CCC remained relatively high in the Main Hawaiian Islands in the absence of recorded widespread disturbances; declined and subsequently recovered in Mo'orea following a crown-of-thorns sea star outbreak, coral bleaching, and major cyclone; decreased and remained low following coral bleaching in the Florida Keys Reef Tract; and decreased following coral bleaching and disease in St. John. Coral taxa have diverse calcification rates and susceptibility to disturbances characterized by their life history strategies. As a result, changes in CCC over the time series in this study were driven by a combination of shifts in both overall coral cover and in the contributions of calcification by the dominant calcifying coral taxa to CCC. Analysis of coral life history strategies showed that ‘weedy’ corals increased their contributions to CCC over time while ‘competitive’ corals decreased. Conversely, shifts in contributions by ‘stress-tolerant’ and ‘generalist’ corals to CCC varied by taxa across the regions. The increasing frequency and intensity of disturbances under 21st century global change is therefore predicted to affect CCC for many coral reefs with potentially lower and more variable CCC sustained under increased disturbance regimes by the increasing dominance of ‘weedy’ and some ‘stress-tolerant’ corals.