Microhabitat factors affecting abundance and diversity of Conus on coral reefs

Frequency and per cent cover of particular substratum types are shown to be important factors influencing abundance and diversity of mobile, predatory benthic invertebrates on spatially complex coral reef platforms. The most favorable portions of reefs for the gastropod Conus have <20% cover of algal-bound sand and <20% cover of living coral. The former microhabitat provides diurnal shelter for smaller Conus, harbors dense prey populations, and is typically interspersed with sand- and rubble-filled depressions in which many of the gastropods shelter during the day. In Micronesia and Australian Great Barrier Reef censuses, 39 1x10-m transects on favorable habitat supported an average of 7 Conus of 3 species. In striking contrast, portions of reef with >20% living coral are most unfavorable for Conus. Here density averaged 0.3 individual/10 m², in 17 transects. Living coral harbors few suitable prey organisms, and contact with it elicits a strong avoidance response by Conus. Comparison of subtidal reef and intertidal bench habitats indicates that species diversity and population density are inversely related, but within both habitat types these attributes of Conus assemblages are positively associated.