(Georgia Institute of Technology, 1995-03-23)
Cronin, Greg; Hay, Mark E.; Fenical, William; Lindquist, Niels Lyle
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.
(Georgia Institute of Technology, 1995-03-23)
Cronin, Greg; Lindquist, Niels Lyle; Hay, Mark E.; Fenical, William
Investigations focused on the ecological roles of marine secondary metabolites have become common, but marine ecologists have rarely assessed how methodologies used in sample preparation affect the extractability and stability of secondary metabolites and, thus, measurements of intraspecific and interspecific compound variance. We assessed various procedures for storing, drying, and extracting samples of 2 chemically defended brown seaweeds Dictyota ciliolata and D. menstrualis. These plants contain the diterpenoid alcohols pachydictyol A, dictyol B acetate, and dictyol E that are relatively stable under all test conditions. In contrast, the related diterpenoid dialdehyde, dictyodial, decomposed when plant tissues or crude extracts were stored at -25°C for 13 to 27 wk or when tissues or extracts were freeze-dried or subjected to high vacuum (<0.01 torr), methods that are commonly used in studies of marine chemical ecology. The stability of dictyodial was species-specific, degrading more in D. ciliolata than in D. menstrualis. During a few extractions, dictyodial reacted with methanol (MeOH) to yield an artifact resulting from the addition of 2 molecules of MeOH per molecule of dictyodial. A mixture of 2:1 dichloromethane (DCM) and MeOH tended to extract the lipophilic secondary metabolites better than MeOH or DCM alone. Metabolites were also afforded some protection against degradation when fresh tissue was submerged in 2:1 DCM:MeOH during storage at -25°C. Results of this investigation indicate that storage, extraction, and quantification methods need to be optimized for analyses of individual compounds and that even identical compounds can behave differently when they occur in different species.