Hermit Crab-Sea Anemone Associations

My research has focused on studying adaptations among symbiotic cnidarians and their associates. In particular, the sea anemone Calliactis tricolor lives exclusively on gastropod shells occupied by hermit crabs. These associations are mutualistic because both the crab and anemone can protect each other from predation. It is not known how these symbionts initiate these associations in the field. Laboratory studies show that the crab can manipulate the anemone to release its pedal disc. The anemone then aids in the completion of the transfer by clinging to the new shell with its tentacles until it can somersault and reattach its pedal disc.

The current research project looked at factors influencing this transfer behavior of C. tricolor. In experiments conducted at Florida Atlantic University and Duke University Marine Laboratory, Leah Ceperley (a Cosen-Pew, Kenyon College undergraduate visiting researcher at Duke), Juan Gutierrez (an FAU undergraduate who also was a visiting researcher at Duke), Dr. Dan Rittschof (a Duke professor), and I looked specifically at the effects of time since detachment of the anemone, texture, and chemical composition of the settlement surface. We tested individual detached anemones and used tentacle-adhesion to mollusc shells or glass slides to measure anemone responses. We found the following results for C. tricolor: (1) responses to shells were most pronounced within the first 30 minutes after detachment; (2) attachment to shells with the organic matrix removed (by baking at 500° C) was reduced; and (3) adsorption of complex odors that signal food or trigger shell investigation (i.e., degraded snail flesh) on baked shells or textured (sintered) slides increased anemone responses.

In short, for a brief time after detachment or disturbance, textural and chemical cues stimulate C. tricolor to transfer. Some of these odors are the same ones that trigger hermit crabs to search for and exchange shells. These results indicate that the anemone and hermit crab coevolved similar responses to facilitate the symbiotic association. Tests of this hypothesis could be done on hermit crab-anemone associations in which the partners have unequal roles in the transfer process. For example, C. polypus apparently displays little response to snail shells and relies almost entirely on its hermit crab host to initiate and complete the transfer. Coevolved chemical mediation would be less likely in this latter case. We hope to explore this hypothesis in future research.