Fouling and gastropod predation: consequences of grazing for a tropical octocoral

Abstract

The ovulid gastropod Cyphoma gibbosum Linnaeus is a specialist consumer of gorgonian octocorals. Although the direct effects of its feeding do not appear to be great, the indirect consequences may be substantial. An 8 wk study of the gorgonian Plexaura homomalla Esper in Curacao found that C. gibbosum occurred primarily on the lower 30 cm of colonies, and that there were significant correlations between C. gibbosum density and the extent of colony fouling on the lower 30 cm of colonies. This correlation occurred whether one measured initial fouling, final fouling, or change in fouling during the 8 wk. There were no significant correlations of C. gibbosum density and fouling for colony portions more than 30 cm above the holdfast. These findings and direct observations in the field suggest that feeding by C. gibbosum increases fouling of gorgonians by exposing the axial skeleton and providing setting sites for fouling propagules. Because fecundity of P. homomalla is reduced when fouling separates colonies into a series of smaller aggregates, the indirect effects of C. gibbosum grazing could strongly affect the fitness of P. homomalla and other gorgonians