GLOBAL CORAL REEF BLEACHING AND SEA SURFACE TEMPERATURE TRENDS FROM SATELLITE-DERIVED HOTSPOT ANALYSIS

Coral reefs are among the first ecosystems threatened by global climate change: since 1982, repeated episodes of high sea temperature and large-scale bleaching stress have imposed accelerating and unprecedented morbidity and mortality in coral reefs, affecting even the most remote areas unstressed by direct human impacts. Analyses of global satellite-derived sea surface temperature anomalies and coral reef bleaching reports since 1982 show that both are rapidly increasing. During 1998 record numbers of reef-building corals died following exposure to abnormally warm waters in the Indian Ocean, Western Pacific Ocean, and Caribbean. Although temperatures were higher In the Eastern Pacific Ocean in 1998 than in 1983, mortality was lower, perhaps because only high temperature tolerant corals had survived. Sea surface temperature trends for 207 coral reef sites since 1984 show average increases of 0.32o C / decade, more than twice average global warming rates, and show strong regional and latitudinal patterns. These tendencies indicate that tropical waters are warming faster than temperate and boreal zones, in contrast to most climate model simulations, and imply that large-scale regional changes in ocean circulation may be taking place. Bleaching has occurred in locations both positively and negatively correlated with the concurrent El Nino Southern Oscillation Index (ENSO). Sub-threshold bleaching events, due to other than high temperature causes, are infrequent and appear to be declining slightly. Near threshold bleaching events linked to near critical, but non-fatal, temperature anomalies have until recently dominated the record, but appear to be increasing slightly with time. Supra-threshold bleaching events with temperatures above critical levels, followed by catastrophic mortality have recently been increasing significantly with time, and now dominate our records. ENSO-like periodicity in bleaching reports may result from global warming driving El Nino events above regional temperature thresholds in those areas with strong positive ENSO correlations, however bleaching events will soon approach