Interactions between trophic levels on coral reefs: Scleractinian corals and corallivorous butterflyfishes in Hawaii

Abstract

Resource use by coral feeding butterflyfishes (Family Chaetotondidae) was studied at 6 geographic sites in the Hawaiian Islands. There was little diet overlap between the specialist species, Chaetodon unimaculatus and the generalist species, Chaetodon multicinctus, C. ornatissimus, and C. trifasciatus. Although there was high diet overlap between the generalist species, C. multicinctus showed a strong feeding preference for the coral Pocillopora meandrina. Chaetodon ornatissimus fed on corals roughly in proportion to their abundance, and C. trifasciatus, contrary to laboratory feeding preferences for pocilloporids and montiporids, fed on Porites spp. in the field. The specialist, C. unimaculatus, preferred Montipora spp. at all sites, and there was a trend towards a relationship between C. unimaculatus densities and coral cover of Montipora spp. There was no correlation between overall butterflyfish densities and coral cover at these sites. Butterflyfishes used non-overlapping feeding ranges intra-specifically, but showed high inter-specific overlap. Chaetodon multicinctus, the smallest bodied species, used the smallest areas and showed the most aggressive interactions against conspecifics and other butterflyfishes. The effects of grazing by butterflyfishes on coral was investigated with the Hawaiian coral Montipora verrucosa. M. verrucosa colonies, protected from the butterflyfishes with wide mesh cages, were compared to their clonemates exposed to predation. Although reproductive output was highly variable among clones, gamete weight per unit surface area of grazed clonemates was signficantly greater than their ungrazed clonemate. Ramets protected from butterflyfishes, however, had twice the linear growth as grazed ramets. These results corroborate the predictions of Williams (1975) Strawberry-Coral Model for the allocation of resources to reproduction in clonal organisms. Photosynthetic and respiratory rates were measured in a laboratory respirometry setup. Respiration rates and maximum photosynthetic capacity were the same for grazed and ungrazed clonemates. Parameters for light saturation curves for photosynthesis for clonemates were not significantly different, suggesting that energy available from the symbiotic zooxanthallae in protected clonemates was used to fuel rapid growth and in grazed clonemates to repair tissues and increase sexual reproduction.