Patterns in the distribution of macrofaunal communities in coral reef sediments on the central Great Barrier Reef

Abstract

The sediment environment and fauna from 6 reefs in a broad transect across the central Great Barrier Reef were quantitatively surveyed. Four distinct sediment types were present. Two were only found on the inner-shelf reefs; both contained high levels of siltlclay. The sediment from the more exposed inner-shelf site contained significant amounts of broken shell. The others were almost exclusively reef derived carbonates from middle and outer shelf reefs. One was predominantly coarse sand and gravel from the shallow reef flat, the other mainly medium to fine sand from the lagoon. There were major differences in the fauna from the inner, middle and outer shelf reefs, whereas the fauna from different depth zones and sediment types within reefs showed less extreme differences. Contrary to expectation, sedirnents of similar type from the middle and outer shelf reefs did not support similar infaunal communities. Crustaceans (particularly amphipods), which were a significant component on the middle shelf reefs, were a very minor part of the sediment fauna on the outer shelf. Small changes in the sediment fauna occured over periods of a few months to a year, but major patterns persisted throughout the year. It is suggested that differences are maintained by a combination of mechanisms; larval availability (determined by water currents) interacts with habitat selection and differential survival. The short generation times and variety of life history tactics of sediment animals predispose this component of the reef fauna as a tool for the study of recruitment on coral reefs. 'Sirius' and K. Weaver for assistance in the field; I. Loch, W. F. Ponder W. B Rudman. T Cochran and S. Slacksmith for identification of the molluscs.