Spatial patterns in shallow-water crinoid communities on the central Great Barrier Reef

Abstract

The crinoid communities of shallow-water areas (<12 m depth) of the central Great Barrier Reef were investigated on reefs at different locations on the continental shelf and in greater detail within one mid-shelf reef (Davies Reef). Overall, 43 comatulid crinoid species were identified, among which the family Comasteridae contributed 90% of the total number of collected specimens. High substratum complexity, in combination with high average water flows, characterized the most suitable environmental conditions for most of the crinoid species, whereas abundance and species richness were low in regions with high sedimentation rates and low current velocities. This set of environmental factors was correlated with crinoid community structures both on a local within-reef level and across the continental shelf. A few 'generalist' species (mostly comasterids) showed distribution ranges extending across the 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 inner and the outer shelf edges. Crinoid populations on reefs previously infested by Acanthaster planci were depleted in comparison with unaffected reefs. Observations suggest that the spangled emperor fish (Lethrinus nebulosus) is a major crinoid predator and that fatal predation occurs commonly among crinoids.