Date of Award

Spring 1989

Project Type


Program or Major


Degree Name

Doctor of Philosophy


The purpose of this study was to document the biological interactions in a predator-prey relationship involving a nudibranch and hydroid, respectively. The predator is a hermaphroditic opisthobranch mollusc with direct development, Cuthona nana. Cuthona nana feeds specifically on the colonial hydroid Hydractinia echinata.

Population patterns of predator and prey were documented by collecting hermit crabs with hydroid-covered shells. Results indicate a subannual life cycle for C. nana with juveniles and egg masses present throughout the year. Hydractinia echinata colonies reproduce in the spring and are more abundant in late summer and early fall.

Field and laboratory observations indicate that adult nudibranchs leave hydroid colonies to lay egg masses. Adults moved on and off of colonies while juveniles did not leave the colonies on which they were originally placed. The crab seems to play a part in bringing food to newly hatched juvenile or adult nudibranchs on the bottom.

The maintenance of this species-specific association can be explained by partial predation of the colonies. Spines prevent complete removal of tissue. Hydroid colonies are capable of regeneration and can withstand cropping by nudibranchs. Hermit crab movement may be positive for both the nudibranch and hydroid. The hydroid obtains food from the sandy bottom as the crab moves about and is also moved away from predators. Nudibranchs can be dispersed by crab movement and also obtain food if a crab has a hydroid colony on its shell. (Abstract shortened with permission of author.).