Ecology of Conus on Seychelles reefs at mid-twentieth century: comparative habitat use and trophic roles of co-occurring congeners

Abstract

This comparative ecological study of 33 species of the predatory gastropod Conus in coral reef-associated habitats in Seychelles emphasizes variation in species composition, diversity, and population density with environmental attributes, and use of food and space resources by co-occurring congeners. Topographically simple but physically harsh intertidal benches supported eight or nine species of generally small body size [mean shell length (SL) 22 mm] but relatively high population density (0.2 m⁻²). Structurally more complex, physically benign, subtidal coral reef platforms supported more species (7–19, mean = 12) of much broader size range and larger mean SL (41 mm), but at lower population densities (0.02–0.14 m⁻²). Most species (85 %) preyed on polychaete worms. One preyed exclusively on a hemichordate worm, two on fishes, and three on gastropods. In general, species specialized more on different prey taxa than different microhabitats. These results are generally consistent with those previously reported for Conus spp. assemblages in similar habitats elsewhere in the tropical Indo-Pacific. They support the hypotheses that (1) resource partitioning, especially of food resources but also of microhabitats, facilitates assemblages of numerous co-occurring Conus spp. and their avoidance of interspecific competition, and (2) ecological differentiation has contributed importantly to the striking Cenozoic adaptive radiation of Conus. The fieldwork, in 1957–1958, also provides baseline data for future studies of how changing marine environmental conditions affect coral reef-associated biotas.