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SHEDDING LIGHT ON CORALS HEALTH: INTERACTIONS OF CLIMATE CHANGE AND SOLAR RADIATION WITH BLEACHING
Citation:
Zepp, R G. SHEDDING LIGHT ON CORALS HEALTH: INTERACTIONS OF CLIMATE CHANGE AND SOLAR RADIATION WITH BLEACHING. Presented at Corals Reefs, Climate, and Coral Bleaching Workshop, Oahu, HI, June 18-20, 2003.
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:
Coral bleaching and declines in coral reef health in recent years have been attributed in part to processes driven by UV and/or visible light. For coral assemblages, exposure to UV light is often an unavoidable consequence of having access to visible (photosynthetically active) radiation. UV exposure can potentially affect corals by damage to DNA or by damage to other target molecules, including proteins that are part of the photosynthetic system. Changes in environmental conditions such as increased temperature or other factors can influence adverse responses of corals to UV and visible light by altering mechanisms that protect the corals from light damage. In addition to effects on responses of corals to UV light, changes in environmental conditions can also have pronounced effects on the nature and amount of light that reaches the surface of corals, especially in the UV region. Changes in atmospheric composition, especially in total ozone, have important effects on the UV-B (280 - 315 nm) part of solar radiation that reach the ocean surface. In addition, changes in UV exposure can stem from shifts in UV-absorbing dissolved and particulate organic matter in the ocean. Recent research has shown that the colored component of dissolved organic matter (CDOM) controls the penetration of solar UV and blue radiation into waters over the many coral reefs. Light exposure of the CDOM in the upper ocean causes it to decompose and the resulting decrease in UV light absorption can enhance UV exposure of coral reefs, especially under well-stratified conditions such as those that develop during El Nino events. The CDOM is introduced to the water by decomposition of aquatic plants (e.g. algal detritus and seagrasses) and by runoff from nearby terrestrial ecosystems. Changes in salinity and land use, coupled with precipitation, sea level and current changes, can have important effects on CDOM sources that affect corals light exposure.