A comparison of the ecology of shallow subtidal gastropods between western Indian Ocean and Caribbean coral reefs

Abstract.

I studied the ecology of snails inhabiting shallow wave-protected subtidal coral reef seascapes on the down-welling eastern edge of the American (Florida Keys and Belize) and African (Kenya and Madagascar) continents. Snail population abundance (CPUE), body sizes, modes of feeding, numbers of species, and species diversity were compared between regions and ocean basins. The Caribbean region had a third the number of species above 50 h or 5,000 individuals of sampling and higher dominance. When analyzed as numbers of individuals, the Caribbean community had a greater abundance of herbivorous and detritivorous individuals compared to the western Indian Ocean region. When analyzed as a percentage of species, there were no trophic differences, with two thirds of the species being carnivorous and one third herbivorous or detritivorous in both ocean basins. Body sizes were also not different in analyses based on either species or population abundance, but the Caribbean sites had higher variation in body size than the western Indian Ocean. The trophic, dominance, and species richness data suggest that the Caribbean assemblage has been influenced by environmental stress, but body-size data do not reflect this pattern unless stress increases variation rather than decreases body size. Recent environmental conditions may account for differences in the population dominance of trophic categories, but differences in species richness has required many millions of years of differential species origination and extinction.