Abstract

The Florida Reef Tract is the third largest barrier-bank reef in the world and has provided considerable ecological services to the local economy of the Florida Keys through commercial and sport fishing as well as tourism. Coral reefs are adapted to oligotrophic conditions and low level nutrient enrichment from anthropogenic sources can lead to eutrophication and loss of these vital resources. Long-term water quality monitoring of dissolved inorganic nitrogen, soluble reactive phosphorus, and chlorophyll a at Looe Key reef in the lower Florida Keys, established as a Marine Protected Area in 1983, has shown a doubling of these variables between 1984 and 1998. The most dramatic nutrient enrichment occurred between 1991 and 1995 when water managers increased flows of nitrogen-rich agricultural runoff from the Everglades into the Florida Bay/Florida Keys region. The long-term nutrient enrichment correlated with decreased coral cover, increased coral disease, and increased cover of algae, bioeroding sponges, soft corals, and other opportunistic biota. Comparisons among fish censuses in the early 1980s and in 2002 indicate that the relative abundances of snapper, grouper, and grunt assemblages decreased by 75 % at Looe Key, whereas the herbivorous fish assemblage doubled in relative abundance. Measurement of stable nitrogen isotopes in macroalgae provide a useful means of quantifying the relative importance of various nitrogen sources, such as natural nitrogen fixation, wastewater, fertilizers, and atmospheric deposition. These data demonstrate the sensitivity of coral reefs to nutrient enrichment and the importance of water quality management to the survival of coral reefs, associated fisheries and ecological services.

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