STRUCTURAL AND CHEMICAL DEFENSES OF ECHINODERMS FROM THE NORTHERN GULF-OF-MEXICO

The feeding deterrent effects of echinoderm body-wall tissues and etha nolic extracts containing mid-polarity compounds were evaluated utiliz ing generalist fish and crabs as model predators. The body-wall tissue s of the echinoderms examined ranged 10-fold from 0.9-9.4 mm in thickn ess, and four and a half-fold in level of mineralization (17.8-82.7% a sh content). Holothuroids had the thickest body-wall tissues and conta ined the lowest levels of mineralization in their body-walls. Crinoids and ophiuroids had high levels of mineralization in their arms. Aster oid body-wall tissues varied the most in thickness and ash content (0. 9-3.9 mm in thickness and 29.2-55.5% in ash content). Body-wall tissue s of 19 species of echinoderms were tested for their feeding deterrent properties against the marine fishes Lagodon rhomboides (Linnaeus) an d Cyprinodon variegatus (Lacepede), as well as the decapod crustacean Libinia emarginata (Leach). Equivalent sized pieces of fresh body-wall tissue of 16 species of echinoderms caused observable feeding deterre nce responses in at least two of the three model predators. There was no significant correlation between body-wall thickness or percent ash and its palatability to any of the three model predators. Agar pellets containing ethanolic body-wall extracts of 12 of 18 echinoderm specie s caused observable feeding deterrence responses in the fish L. rhombo ides. In similar experiments with the arrow crab Stenorhyncus seticorn is (Herbst), using carrageenan fish-meal blocks as food models, no dif ferences in consumption of control fish-meal and experimental body-wal l extract blocks were detected. Our findings indicate that invertebrat e and vertebrate predators may respond quite differently to echinoderm body-wall extracts. (C) 1997 Elsevier Science B.V.