SETTLEMENT AND RECRUITMENT OF QUEEN CONCH, STROMBUS-GIGAS, IN SEAGRASS MEADOWS - ASSOCIATIONS WITH HABITAT AND MICROPREDATORS

A suction dredge survey was conducted in the Bahamas in a tidal flow f ield system which contained a nursery ground for the economically sign ificant gastropod Strombus gigas (queen conch). Settlement of larval c onch within the system was associated with the specific location of th e nursery and positively correlated with subsequent recruitment to the juvenile population (<45 mm shell length). Settlement was relatively independent of habitat features including depth, sediment characterist ics, and macrophytes. Conversely, densities of micro-predators (small crabs, shrimp, and predaceous gastropods) capable of consuming early p ostsettlement conch were often correlated with habitat features such a s seagrass shoot density, seagrass detritus, and organic content of th e sediment. The density of small xanthid crabs (mode=1.5 mm carapace w idth) was positively correlated with density of live postsettlement co nch (mean less than or equal to 4/m(2)), suggesting that conch settle in predator-prone areas or that the crabs respond numerically to small conch (or both). Densities of xanthids were very high (to >200/m(2)), and the crabs probably represent an important source of mortality for small conch in the primary nursery ground. Shells of dead conch indic ated that molluscan and asteroid predators probably caused most of the predatory mortality on young conch that settled outside the nursery. Because critical settlement and recruitment habitats for queen conch a re associated with particular hydrographic conditions, these habitats cannot be identified or predicted simply by mapping obvious features s uch as seagrass cover, depth, or sediment type. An understanding of dy namic processes, such as larval transport and retention, selective set tlement mechanisms, and trophic ecology, will be required to identify critical nursery habitats.