THE FUTURE OF CARIBBEAN CORAL REEFS

Caribbean reef development and community composition were remarkably stable for the past 1-2 Ma but are now severely threatened by human disturbance on local and global scales. Average coral cover at 90 reef locations from Bermuda to South America declined by half since 1970 while macroalgae increased 3-fold. Most of the decline occurred before the first outbreaks of coral bleaching so that climate change was not responsible. Moreover, coral cover has been more stable and macroalgae rare at locations protected from overfishing and pollution, suggesting that local human impacts have been the major drivers of coral decline up to now.

White Band Disease virtually eliminated acroporid corals from most reefs in the 1980s while other corals have been more resilient to disease. The causes of disease outbreaks are unknown, but some may have been introduced through the Panama Canal. Increased pathogen diversity and abundance due to declining water quality may also be important factors. Extreme heating events and coral bleaching caused extensive coral mortality on overfished reefs where abundant macroalgae increase the likelihood of coral disease and inhibit coral recruitment and growth. Extreme heating events have had little impact on protected reefs.

Two outstanding questions for the long-term future of Caribbean reefs are (1) the extent to which strong local protections from overfishing and pollution can continue to confer coral resilience to rising temperatures and declining pH, and (2) and the possibility of coral adaptation to these harmful consequences of climate change. Reef composition will almost certainly change with the likely loss of fast growing branching corals and increased dominance of more physiologically resilient massive species. Nevertheless, much could be done in the meantime to reverse the decline of Caribbean reefs by effective regulation of overfishing and coastal development.