Using remote sensing to reassess the mass mortality of Diadema antillarum 1983-1984

The 1983-1984 mass mortality of the sea urchin Diadema antillarum remains o ne of the most severe die-offs ever recorded in the Caribbean. Before 1983, the herbivore D. antillarum was pervasive on coral reefs in the region. Ni ne months after first detection of the mass mortality, 95% of the urchins h ad perished, and algal cover of coral increased between 100% and 250%. A wa ter-borne pathogen was hypothesized as the causative agent, but it was neve r isolated. To date, surface current patterns have been used exclusively to explain both the cause and the distribution patterns of The mortality even t. Using archived satellite images, were-examined the water-borne pathogen hypothesis and investigated whether other mechanisms could also account for the dissemination pattern in some areas. In addition, archived satellite i mages were utilized to detect changes in coral reef reflectance, For infect ions in the Gulf of Mexico and Bermuda, satellite images confirm that surfa ce currents are likely responsible for the distribution of the pathogen. Fo r infections in the eastern Caribbean (Curacao, U.S. Virgin Islands, Barbad os), however, another mechanism, possibly ballast water exchange, must be c onsidered because the surface current and infection patterns do not coincid e. Changes in coral reflectance were detectable from Landsat thermatic mapp ing data before and after the mass mortality and correspond to the change i n algal cover. Results from our study demonstrate the Potential of satellit e images for use in determining connectivity between regions of the Caribbe an and in detecting changes in coral reef cover.