Coral reef bleaching and global climate change: can corals survive the next century?

Abstract

Coral reef ecosystems are threatened on a worldwide basis, with overfishing, diseases, eutrophication, hurricanes, overpopulation, and global climate change all contributing to recent declines in reef-forming corals or phase shifts in community structure on time scales not observed previously (1–3). These changes are in contrast to recent periods of long-term stability in coral reef communities over geological time scales of thousands of years (4, 5). A recent meta-analysis of coral cover throughout the Caribbean has shown an 80% decline that has been both long term (e.g., decadal) in duration and region-wide (6). For the last two decades, coral reef biologists have attributed much of the increase in coral mortality to coral bleaching subsequent to elevated seawater temperatures occurring on both regional and global spatial scales (7). Coral bleaching, a stress response of reef-forming corals, results in the loss of their symbiotic algal partner that supplies a large percentage of the nutritional requirements of the coral host and causes the corals to appear white (ref. 7 and Fig. 1). Since 1979, there have been dozens of reports of coral bleaching associated with elevated sea surface temperatures (SSTs), whereas from 1876 to 1979, only three events were recorded (8). The recently released Fourth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC; www.ipcc.ch) states with 90% certainty that most of the observed warming of the planet over the last half-century has been caused by human activities from the accumulation of greenhouse gases. On the heels of the IPCC report, in this issue of PNAS, Donner et al. (9) provide a quantitative assessment of the contribution of human-induced climate change for the most devastating coral-bleaching event on record, the Caribbean-wide coral bleaching in 2005.