Cross-shelf patterns in the community structure of coral-dwelling Crustacea in the central region of the Great Barrier Reef. II. Cryptofauna

Abstract

The crustacean cryptofaunal assemblages associated with live and dead Pocillopora verrucosa were sampled from isolated coral heads placed at leeward and windward zones of an inner shelf, a mid-shelf and an outer shelf reef. At spatial scales from 1 m to 90 km there was pronounced variation in cryptofaunal abundance. Prior to bioerosion of the corals, reef location was the dominant determinant of total abundance with subordinate, taxon-specific, effects of exposure. The cryptofaunal assemblages on living and dead corals on the mid- and outer shelf reef were dominated by copepods with maximum abundance on the back reef sites of the mid-shelf reef. Total abundance was significantly lower on the inner shelf reef, which had a distinctly different assemblage characterised by fewer copepods and greater numbers of ostracods, cumaceans and tanaids. At all locations, sediment accumulated on the corals but in creater amounts on dead ones. Types of sediment trapped by corals appeared to be an important determinant of cryptofaunal composition. At the cross-shelf scale, higher abundance of the predominantly copepod assemblages on the mid-shelf reef may be indicative of elevated primary productivity in this region. At the reef scale, differences in sediment composition and rates of bioerosion among zones (windward and leeward sites) may influence asemblage sturcture. At the replicate scale, among individual coral heads, both the abundance and composition of crustacean cryptofauna may be influenced by microhabitat features. -from Authors