Prey preferences and browsing pressure of the butterflyfish Chaetodon capistratus on Caribbean gorgonians

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Abstract
The Caribbean butterflyfish C. capistratus Linnaeus usually feeds on scleractinian corals, but at a site in the San Blas Islands, Panama, C. capistratus fed primarily on gorgonians; it fed mainly on polyps, did not feed on gorgian colonies when the polyps were contracted and fed primarily on large colonies. Plexaura homomalla was the most preferred prey species. An undetermined Plexaura sp., terminated Plexaura A, and Pseudopterogorgia americana were also browsed heavily. During May, June and July 1981, 1982 and 1983, feeding on Plexaura A followed a lunar cycle in which large colonies were browsed during or shortly after full moon. Examination of Plexaura A goada samples suggests that C. capistratus feeding was correlated with gorgonian spawning. During Jan. 1984, when gonads were small, Plexaura A was rarely fed upon regardless of lunar phase. Extrapolation of feed rates indicates that Plexaura homomalla colonies lose an average of 378 polyps day-1 to browsing and Pseudopterogorgia americana colonies lose 100 polyps day-1 to browsing by C. capistratus. These daily removal rates corresponds to the number of polyps found on 5 to 10 cm of branch. The average Plexaura A colony lost only 19 polyps day-1, but 1 colony suffered a maximum single-day loss of 1620 polyps. These data suggest that browsing by C. capistratus can cause a significant loss of biomass in a number of gorgonian species.
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