Changes in Structure of Coral Reef Fish Communities by Destruction of Hermatypic Corals: Observational and Experimental Views

Abstract

Population outbursts of the crown-of-thorns starfish, Acanthaster planci, have drastically altered communities in many coral reef areas of the Indo-west Pacific since the late 1960s. To understand the pattern of changes in fish communities on damaged coral colonies, direct observations and field experiments were carried out in inshore waters at Minatogawa, Okinawa Island (26°16' N, 127°42' E), in 1979 and 1980. From experiments on the effects of coral death and on the effects of decreased structural complexity of coral branches on fish communities using five colonies of staghorn coral, Acropora sp., we were able to predict the following changes in fish communities resulting from the destruction of living corals by Acanthaster. Coral polyp feeders completely disappear from dead coral colonies due to absence of their food; and the numbers of resident species and individuals decrease due to the reduction in living space or shelter when the structural complexity of dead coral colonies is decreased by bio- and physical erosion. Consequently, fish species diversity also decreases. These predicted changes are consonant with those directly observed on nine natural dead staghorn coral colonies.