CORAL REEFS
Symbiotic crabs maintain coral health by clearing sediments
Hannah L. Stewart1 Contact Information, Sally J. Holbrook1, 2, Russell J. Schmitt1, 2 and Andrew J. Brooks1
(1) Coastal Research Center, Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA 93106, USA
(2) Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA
Received: 18 March 2006 Accepted: 2 June 2006 Published online: 26 July 2006
Communicated by Biology Editor H.R. Lasker
Abstract Stony corals are the foundation of coral reef ecosystems and form associations with other reef species. Many of these associations may be ecologically important and play a role in maintaining the health and diversity of reef systems, rendering it critical to understand the influence of symbiotic organisms in mediating responses to perturbation. This study demonstrates the importance of an association with trapeziid crabs in reducing adverse effects of sediments deposited on corals. In a field experiment, mortality rates of two species of branching corals were significantly lowered by the presence of crabs. All outplanted corals with crabs survived whereas 45â€"œ80% of corals without crabs died within a month. For surviving corals that lacked crabs, growth was slower and tissue bleaching and sediment load were higher. Laboratory experiments revealed that corals with crabs shed substantially more of the sediments deposited on coral surfaces, but also that crabs were most effective at removing grain sizes that were most damaging to coral tissues. The mechanism underlying this symbiotic relationship has not been recognized previously, and its role in maintaining coral health is likely to become even more critical as reefs worldwide experience increasing sedimentation.
Symbiotic crabs maintain coral health by clearing sediments
Hannah L. Stewart1 Contact Information, Sally J. Holbrook1, 2, Russell J. Schmitt1, 2 and Andrew J. Brooks1
(1) Coastal Research Center, Marine Science Institute, University of California Santa Barbara, Santa Barbara, CA 93106, USA
(2) Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA
Received: 18 March 2006 Accepted: 2 June 2006 Published online: 26 July 2006
Communicated by Biology Editor H.R. Lasker
Abstract Stony corals are the foundation of coral reef ecosystems and form associations with other reef species. Many of these associations may be ecologically important and play a role in maintaining the health and diversity of reef systems, rendering it critical to understand the influence of symbiotic organisms in mediating responses to perturbation. This study demonstrates the importance of an association with trapeziid crabs in reducing adverse effects of sediments deposited on corals. In a field experiment, mortality rates of two species of branching corals were significantly lowered by the presence of crabs. All outplanted corals with crabs survived whereas 45â€"œ80% of corals without crabs died within a month. For surviving corals that lacked crabs, growth was slower and tissue bleaching and sediment load were higher. Laboratory experiments revealed that corals with crabs shed substantially more of the sediments deposited on coral surfaces, but also that crabs were most effective at removing grain sizes that were most damaging to coral tissues. The mechanism underlying this symbiotic relationship has not been recognized previously, and its role in maintaining coral health is likely to become even more critical as reefs worldwide experience increasing sedimentation.
