Aspects of Corallivory by Chaetodon unimaculatus in Kane'ohe Bay, Oahu

Abstract

Interactions between a corallivore, Chaetodon unimaculatus, and the two dominant coral species in Kane'ohe Bay, Montipora verrucosa and Porites compressa, were investigated. Feeding selectivity was tested in laboratory and field observations, with the fish clearly selecting M. verrucosa: 39:1 bites in laboratory trials and 284:1 bites in field observations. Using an estimated bite size of 2.54 mg AFDW and two estimated feeding rates, 4.88 bites min-1 during the "dry" season (May to September) and 7.20 bites min-1 during the "wet" season (October to April), an average sized fish consumes approximately 4000 g of coral tissue each year, and the population of C. unimaculatus on Patch Reef #42 is removing approximately 10% of the standing crop of M. verrucosa each year. A series of experiments was designed to measure the effect of predation by these fish on growth and competition between the two corals. Caged colonies of M. verrucosa at Patch Reef #42 had a vertical growth rate of 9.71 x 10-3cm day-1, and M. verrucosa killed P. compressa tissue it came in contact with. In uncaged colonies, M. verrucosa grew at a rate of 3.92 x 10-3cm day-1, about 40% of the caged growth rate, and several colonies showed a reversal of aggressive dominance as predicted from previous studies, with P. compressa killing branches of M. verrucosa. On Patch Reefs #42 and #43 there is a significant increase in the percent M. verrucosa with increased distance from the edge of the reef, where the fish are normally found, and grazing pressure is greatest. Because of its selective feeding behavior in Kane'ohe Bay, C. unimaculatus appears to have a significant effect on the growth and distribution of its preferred coral species, M. verrucosa.