Branching corals, like many in the genus Acropora, provide structurally complex habitats for reef fishes and other organisms. Fluctuations in the abundance, distribution and characteristics of staghorn Acroporid corals may contribute to changes in the abundance and species composition of reef fishes due to changes in the availability of shelter habitat and food. Farming damselfishes of the genus Stegastes occur in high abundances in staghorn thickets and actively defend food and nest space against organisms that threaten these resources. Here I examine the value of staghorn thickets as habitat for fishes, and how the presence of territorial farming damselfishes may influence the assemblage of fishes that associate with staghorn corals. Surveys of 185 Acropora pulchra thickets located in the lagoons surrounding the island of Moorea, French Polynesia revealed 85 species of fish from 25 families. Total fish abundance and species richness values ranged from no fish on a thicket to a high of 275 individuals and 26 species. Thicket area was the most important characteristic in explaining variation in attributes of the fish assemblage among staghorn thickets, with other characteristics explaining little of the species composition or trophic structure. Behavioral observations revealed that farming damselfishes were most aggressive toward corallivores, herbivores, and egg predators, while they ignored most carnivores and omnivores. Despite this pattern, I observed positive covariance between Stegastes and the group of fishes that elicited the strongest aggressive response when the effect of thicket area was removed, suggesting these fishes remain drawn to the resources produced or enhanced by Stegastes on A. pulchra thickets.
Thesis or Dissertation
Department of Ecology, Evolution and Marine Biology, UC Santa Barbara