Distribution, density, and sequestration of host chemical defenses by the specialist nudibranch Tritonia hamnerorum found at high densities on the sea fan Gorgonia ventalina

The dendronotid nudibranch Tritonia hamnerorurn was observed on some reefs In the Flonda Keys, USA, at very high densities dunng the summer of 1992 T hamnerorum specializes on the sea fan Gorgonia vental~na and sequesters the furano-germacrene lulieannafuran from its host, this compound effectively protects the nudibranch from consumption by the common predatoiy reef f ~s h Thalassoma bifasciatum T hamnerorum densit~es were extremely hlgh at some locations, with as Inany as 1700 nudibranchs found on a single G ventalina colony At high densities, nudibranch feeding killed large areas on some sea fan colonies by stnpping all tissue from portions of the sea fan and allowing fllamentous algae and other epibionts to colonize The density of T hamnerorum on G ventahna vaned greatly on scales of centimeters meters and k~lometers High density patches of nudlbranchs on individual sea fans were usually composed of equivalent-sized nudtbranchs These observations suggest that pelagic vellgers have an incredible capabil~ty to find and settle synchronously on one portion of a sea fan or that the larvae or luveniles hatch from e g g masses and develop without leaving the sea fan This study adds to a growlng number of m a n n e examples suggesting that feeding specialization occurs pnmardy among small sedentary consumers that deter or escape predators by associating w t h defended hosts