Defense adaptations of the dendrochirote holothurian Psolus chitonoides Clark

Many potentially predatory species of gastropods, decapods, asteroids, and fishes were tested to determine their responses to Psolus chitonoides Clark. Asteroids, particularly Dermasterias imbricata (Grube), were found to be the only important predators. Psolus chitonoides was not found in guts of any field-collected fishes, though other sea cucumbers were. Psolus chitonoides had the highest saponin content of four species of Greater Puget Sound holothurians tested. Homogenates of P. chitonoides were highly unpalatable to the tidepool sculpin, Oligocottus maculosus Girard and tissues were toxic when force-fed to O. maculosus. Toxicity of Psolus chitonoides tissue was due to the high saponin content whereas unpalatability appears to be unrelated to the saponins. Toxicity of saponins from Puget Sound holothurians to Oligocottus maculosus depends on whether the toxin is respired or ingested.