Indirect effects of algae on coral: algae-mediated, microbe-induced coral mortality

Authors

  • Jennifer E. Smith,

    Corresponding author
    1. National Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, 735 State St., Suite 300, Santa Barbara, CA 93101, USA
      * E-mail: jsmith@nceas.ucsb.edu
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  • Morrigan Shaw,

    1. San Diego State University, Department of Biology, Life Sciences 301, 5500 Campanile Drive, San Diego, CA 92182-4614, USA
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  • Rob A. Edwards,

    1. San Diego State University, Department of Biology, Life Sciences 301, 5500 Campanile Drive, San Diego, CA 92182-4614, USA
    2. San Diego State University, Center for Microbial Sciences, 5500 Campanile Drive, San Diego, CA 92182, USA
    3. Fellowship for Interpretation of Genomes, Burr Ridge, IL 60527, USA
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  • David Obura,

    1. CORDIO, East Africa, PO Box 10135, Mombasa 80101, Kenya
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  • Olga Pantos,

    1. San Diego State University, Department of Biology, Life Sciences 301, 5500 Campanile Drive, San Diego, CA 92182-4614, USA
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  • Enric Sala,

    1. Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, University of California, 9500 Gilman Dr, La Jolla, CA 92093-0202, USA
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  • Stuart A. Sandin,

    1. Center for Marine Biodiversity and Conservation, Scripps Institution of Oceanography, University of California, 9500 Gilman Dr, La Jolla, CA 92093-0202, USA
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  • Steven Smriga,

    1. Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0202, USA
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  • Mark Hatay,

    1. San Diego State University, Physics Department 5500 Campanile Drive, San Diego, CA, 92182, USA
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  • Forest L. Rohwer

    1. San Diego State University, Department of Biology, Life Sciences 301, 5500 Campanile Drive, San Diego, CA 92182-4614, USA
    2. San Diego State University, Center for Microbial Sciences, 5500 Campanile Drive, San Diego, CA 92182, USA
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* E-mail: jsmith@nceas.ucsb.edu

Abstract

Declines in coral cover are generally associated with increases in the abundance of fleshy algae. In many cases, it remains unclear whether algae are responsible, directly or indirectly, for coral death or whether they simply settle on dead coral surfaces. Here, we show that algae can indirectly cause coral mortality by enhancing microbial activity via the release of dissolved compounds. When coral and algae were placed in chambers together but separated by a 0.02 μm filter, corals suffered 100% mortality. With the addition of the broad-spectrum antibiotic ampicillin, mortality was completely prevented. Physiological measurements showed complementary patterns of increasing coral stress with proximity to algae. Our results suggest that as human impacts increase and algae become more abundant on reefs a positive feedback loop may be created whereby compounds released by algae enhance microbial activity on live coral surfaces causing mortality of corals and further algal growth.

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