Lack of chemical defense in two species of stalked crinoids: support for the predation hypothesis for mesozoic bathymetric restriction

Methanol/dichloromethane extracts of (1) the arms and pinnules, and (2) the stalk and cirri of the deep water stalked crinoids Endoxocrinus parrae (Ge rvais) and Neocrinus decorus (Carpenter) were imbedded at ecologically rele vant volumetric concentrations in alginate food pellets containing 2% krill as a feeding stimulant and presented in situ to an assemblage of shallow-w ater reef fish. Experimental pellets were highly palatable to reef fish; no significant differences in pellet consumption occurred between experimenta l pellets containing extracts from either species of stalked crinoid or con trol pellets. Small pieces of cirri, stalks, calyx, arms and pinnules of bo th species were also tested in in situ feeding assays. While immediate cons umption by fish was not apparent, Blue Headed Wrasse (Thalassoma bifasciatu m (Block)) and Dusky Damselfish (Stegastes fuscus (Cuvier)) bit at pieces o f each body component. Similar fish biting behaviors were also observed whe n two living Endoxocrinus parrae were deployed on the shallow reef. Observa tions indicate that neither species of stalked crinoid is chemically defend ed from predation by a natural assemblage of reef fish. This supports the p redation hypothesis that restriction of stalked crinoids in deep-water habi tats may have resulted from the Mesozoic radiation of durophagous fishes in shallow seas, resulting in a reduction of stalked crinoids from shallow wa ter. (C) 1999 Elsevier Science B.V. All rights reserved.