SPATIAL PATTERNS IN SHALLOW-WATER CRINOID COMMUNITIES ON THE CENTRAL GREAT-BARRIER-REEF

The crinoid communities of shallow-water areas (<12 m depth) of the ce ntral Great Barrier Reef were investigated on reefs at different locat ions on the continental shelf and in greater detail within one mid-she lf reef (Davies Reef). Overall, 43 comatulid crinoid species were iden tified, among which the family Comasteridae contributed 90% of the tot al number of collected specimens. High substratum complexity, in combi nation with high average water flows, characterized the most suitable environmental conditions for most of the crinoid species, whereas abun dance and species richness were low in regions with high sedimentation rates and low current velocities. This set of environmental factors w as correlated with crinoid community structures both on a local within -reef level and across the continental shelf. A few 'generalist' speci es (mostly comasterids) showed distribution ranges extending across th e whole shelf, whereas many other species were found predominantly at the mid-shelf sites and only in low numbers, if at all, at both the in ner and the outer shelf edges. Crinoid populations on reefs previously infested by Acanthaster planci were depleted in comparison with unaff ected reefs. Observations suggest that the spangled emperor fish (Leth rinus nebulosus) is a major crinoid predator and that fatal predation occurs commonly among crinoids.