Factors affecting food preference in a widespread intertidal isopod

Preference for two macroalgae and feeding rate were influenced by previous experience in the intertidal isopod Dynamene bidentata (Adams). In preference experiments, animals reared in the laboratory with either Fucus vesiculosus L. or Cystoseira baccata (Gmelin) Silva as sole resources did not exhibit preference for either of the two algae. Preference for Fucus was exhibited by the same animals in a subsequent experiment. Specimens reared on Cystoseira exhibited a greater feeding rate than those reared on Fucus. Animals collected in the field on Fucus and Cystoseira preferred Fucus. Digestive efficiency was consistently higher when the animals ate Fucus than when the animals ate Cystoseira. Results suggest that, in D. bidentata, feeding preferences are set after the animals sample the environment for food quality. The existence of a compensatory mechanism in animals kept on suboptimal food resources (Cystoseira) is also suggested.