MEPS 314:119-125 (2006)  -  doi:10.3354/meps314119

Role of elevated organic carbon levels and microbial activity in coral mortality

David I. Kline1,2,3, Neilan M. Kuntz2,3, Mya Breitbart2, Nancy Knowlton1,3, Forest Rohwer2,4,*

1Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA
2Department of Biology, LS301, San Diego State University, 5500 Campanile Dr, San Diego, California 92182, USA
3Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panama
4Center for Microbial Sciences, San Diego State University, San Diego, California 92182, USA
*Corresponding author. Email:

ABSTRACT: Coral reefs are suffering a long-term global decline, yet the causes remain contentious. The role of poor water quality in this decline is particularly unclear, with most previous studies providing only weak correlations between elevated nutrient levels and coral mortality. Here we experimentally show that routinely measured components of water quality (nitrate, phosphate, ammonia) do not cause substantial coral mortality. In contrast, dissolved organic carbon (DOC), which is rarely measured on reefs, does. Elevated DOC levels also accelerate the growth rate of microbes living in the corals’ surface mucopolysaccharide layer by an order of magnitude, suggesting that mortality occurs due to a disruption of the balance between the coral and its associated microbiota. We propose a model by which elevated DOC levels cause Caribbean reefs to shift further from coral to macroalgal dominance. Increasing DOC levels on coral reefs should be recognized as a threat and routinely monitored.

KEY WORDS: Coral reef decline · Dissolved organic carbon · Coral · Montastraea · Bacteria · Caribbean · Nutrients

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