Specialist predation on the Caribbean gorgonian Plexaurella spp. by Cyphoma signatum (Gastropoda)

Abstract

ABSTRACT: The rare marine snail Cyphoma signatum is a trophic specialist on gorgonians Plexaurella spp. A comparative study of this snail species with its generalist congener C. gibbosum showed that feeding behavior differs between the 2 species. Feeding by the specialist often damages the polyps and scleratinlzed matrix of Plexaurella or bares its proteinaceous axis, while the generalist tends to feed pnmarily on the polyps of Plexaurella. As a result, C. signatum ingests more total Plexaurella tissue (including sclerites) and more organic material, though fewer polyps per time, than does C. gibbosurn. Differences in radular morphology are implicated as the proximal cause of species-specific feeding behavior. The lateral teeth of C. signatum are wider and their median teeth have a long central point not present in C. gibbosum, which may enable more extensive wounding of colonies. The feeding behavior of the specialist results in a higher amount of damage to Plexaurella, from which the coral recovers more slowly, as gorgonian regeneration times are inversely proportional to wound depths. Permanent damage to Plexaurella may result when bared proteinaceous axes are fouled by algae or other encrusting organisms. Although the shallow wounds of C, gibbosum are common on Plexaurella, they regenerate within 6 d. Gorgonian censuses at 4 sites showed that high proportions of permanently damaged Plexaurella (250 % permanent damage per colony) were correlated with areas of high C. signatum density. In the short term, predation by C. signaturn appears to increase permanent damage and mortality of Plexaurella. The specialist snail may therefore impose greater selection on the gorgonian than does the generalist. INTRODUCTION