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INDICATORS OF UV EXPOSURE IN CORALS: RELEVANCE TO GLOBAL CLIMATE CHANGE AND CORAL BLEACHING
Citation:
Anderson, S. L., J. Machula, G. Cherr, R G. Zepp, D L. Santavy, L J. Hansen, AND E. Mueller. INDICATORS OF UV EXPOSURE IN CORALS: RELEVANCE TO GLOBAL CLIMATE CHANGE AND CORAL BLEACHING. Presented at Ninth International Coral Reef Symposium, Bali, Indonesia, October 23-27, 2000.
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
Increased exposure to solar UV radiation and elevated water temperatures are believed to play a role in the bleaching of corals. To provide additional tools for evaluating the role of UV radiation, we have examined UV-specific effects in coral and have characterized factors that alter the penetration of UV radiation over coral reefs at sites located in the Florida Keys. Using an immunoblotting assay to examine UV-specific lesions (thymine dimers) in coral and zooxanthellae DNA, we observed dose-dependent increases of thymine dimers in purified coral (Porites porites) DNA exposed to UV-C in the laboratory and with live P. porites exposed in a solar simulator. Field studies conducted at the Florida Key (Maryland Shoals and Eastern Sambo) during July 1999 further demonstrated the utility of this technique in evaluating UV exposure of corals. For example, amounts of thymine dimers in P. porites collected at Maryland Shoals at the time of peak UV exposure (1300 hrs) were significantly higher than at 0830 hrs (p=0.04). UV measurements indicated that the coral reefs at Eastern Sambo (at 3-4 meters) were exposed to UV-B radiation that corresponded to 25-30% of surface UV irradiance. However, the water just inside the reef in Hawk Channel and closer to land was considerably more opaque to UV. This water photobleached with loss of UV absorbance and fluorescence when it was exposed to simulated solar radiation. These results indicate that photobleaching of the DOM and transport of near-shore water out over the reefs may play a key role in controlling UV penetration to the reef surface.