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 sa nd dollar Encope michelini, but after conditioning switched its host prefer ence to a non-field host, the sea biscuit Clypeaster rosaceus. This switch in host preference after conditioning occurred despite consumption of numer ous crabs (86 out of 167) by C. rosaceus. Clypeasterophilus rugatus initial ly preferred its field host, the sea biscuit Clypeaster rosaceus, but showe d little change in host preference after conditioning. These results indica te significant behavioral differences in these closely related crabs in the ir association with echinoderms. Chemical detection by the crabs was invest igated, and no significant use of chemical cues by adults or juveniles of e ither 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 rec eive protection by living with echinoderms was also examined. Crabs with ec hinoderms survived significantly longer than crabs without echinoderms, whi ch is the first direct evidence that these crabs are protected by associati ng with echinoderms.