Host selection, chemical detection, and protection of the symbiotic pinnotherid crabs Dissodactylus crinitichelis and Clypeasterophilus rugatus associated with echinoderms

Host selection by Dissodactylus crinitichelis and Clypeasterophilus rugatus for different echinoderms was investigated. Initial preference (within 24 h of collection) and preference after "conditioning" with an alternate host were compared. D. crinitichelis initially preferred its field host, the sand dollar Encope michelini, but after conditioning switched its host preference to a non-field host, the sea biscuit Clypeaster rosaceus. This switch in host preference after conditioning occurred despite consumption of numerous crabs (86 out of 167) by C. rosaceus. Clypeasterophilus rugatus initially preferred its field host, the sea biscuit Clypeaster rosaceus, but showed little change in host preference after conditioning. These results indicate significant behavioral differences in these closely related crabs in their association with echinoderms. Chemical detection by the crabs was investigated, and no significant use of chemical cues by adults or juveniles of either species was found, even though chemical responses have been observed in other closely related pinnotherid crabs. Using the checkered pufferfish, Sphoeroides testudineus, as a predator, the possibility that crabs may receive protection by living with echinoderms was also examined. Crabs with echinoderms survived significantly longer than crabs without echinoderms, which is the first direct evidence that these crabs are protected by associating with echinoderms.