Chronic parrotfish grazing impedes coral recovery after bleaching
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Coral bleaching, in which corals become visibly pale and typically lose their endosymbiotic zooxanthellae (Symbiodinium spp.), increasingly threatens coral reefs worldwide. While the proximal environmental triggers of bleaching are reasonably well understood, considerably less is known concerning physiological and ecological factors that might exacerbate coral bleaching or delay recovery. We report a bleaching event in Belize during September 2004 in which Montastraea spp. corals that had been previously grazed by corallivorous parrotfishes showed a persistent reduction in symbiont density compared to intact colonies. Additionally, grazed corals exhibited greater diversity in the genetic composition of their symbiont communities, changing from uniform ITS2 type C7 Symbiodinium prior to bleaching to mixed assemblages of Symbiodinium types post-bleaching. These results suggest that chronic predation may exacerbate the influence of environmental stressors and, by altering the coral-zooxanthellae symbiosis, such abiotic-biotic interactions may contribute to spatial variation in bleaching processes.
KeywordsPredation Coral bleaching Trophodynamics Environmental stress Zooxanthellae Symbiodinium
The authors thank Sam Benson, Dan Miller, and Claudette DeCourley for diving assistance; Jeff Chabot for equipment design and data collection; Davey Kline, and Hiro Fukami for species identification; Michael Reed for statistical advice; William Fitt, Gregory Schmidt, James Porter, Ken Sebens, Emily Carrington, Todd LaJeunesse, and Mike Lesser provided insightful comments. Peter Mumby and two anonymous reviewers greatly improved this manuscript. We thank Mike Carpenter and Klaus Ruetzler for their kind support and William Fitt and Gregory Schmidt for their generous lab support and funding for the genetic aspects of this study (NSF 9906976 and 0137007 Fitt). This research was funded by the Smithsonian Caribbean Coral Reef Ecosystems Program (CCRE contribution #718), the Tufts Institute for the Environment, and PADI Project AWARE (to RDR).
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