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does not constitute endorsement or recommendation for use. ii Foreword The overall degradation of coral reefs, measured by declining coral abundance and species diversity as well as increases in macroalgae and reef skeletal erosion, has been documented in the Florida Keys and elsewhere around the world. A widely-recognized aspect of the deterioration of coral reefs is the phenomenon of coral bleaching. Coral bleaching may be the symptom of coral reef degradation that is most closely linked to climate change. Records of coral bleaching from 1870 to the present indicate that the severity, locality, and frequency have reached unprecedented levels. Only three bleaching events were reported between 1876 and 1979, compared to more than 60 bleaching episodes from 1980 to 1993. Most recently, the El Niño Southern Oscillation (ENSO) conditions during 1997-98 induced worldwide bleaching from the Western Atlantic to the Great Barrier Reef. EPA’s Global Change Research Program is addressing potential vulnerabilities due to interactive components of global change that could adversely affect coral reef ecosystems including: (1) climate variability and change; (2) changes in UV radiation; and (3) land use change. This research is designed to complement other EPA research on coastal environment processes, improvements in environmental indicators of coastal conditions, coastal monitoring designs, and assessments that document U.S. conditions and trends in the coastal ocean