Distribution, density, and sequestration of host chemical defenses by the specialist nudibranch Tritonia hamnerorum found at high densities on the sea fan Gorgonia ventalina
Hay, Mark E.
Lindquist, Niels Lyle
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The dendronotid nudibranch Tritonia hamnerorum was observed on some reefs in the Florida Keys, USA, at very high densities during the summer of 1992. T. hamnerorum specializes on the sea fan Gorgonia ventalina and sequesters the furano-germacrene julieannafuran from its host; this compound effectively protects the nudibranch from consumption by the common predatory reef fish Thalassoma bifasciatum. T. hamnerorum densities were extremely high at some locations, with as many as 1700 nudibranchs found on a single G. ventalina colony. At high densities, nudibranch feeding killed large areas on some sea fan colonies by stripping all tissue from portions of the sea fan and allowing filamentous algae and other epibionts to colonize. The density of T. hamnerorum on G. ventalina varied greatly on scales of centimeters, meters and kilometers. High density patches of nudibranchs on individual sea fans were usually composed of equivalent-sized nudibranchs. These observations suggest that pelagic veligers have an incredible capability to find and settle synchronously on one portion of a sea fan or that the larvae or juveniles hatch from egg masses and develop without leaving the sea fan. This study adds to a growing number of marine examples suggesting that feeding specialization occurs primarily among small, sedentary consumers that deter or escape predators by associating with defended hosts.