FACTORS AFFECTING FOOD PREFERENCE IN A WIDESPREAD INTERTIDAL ISOPOD

Preference for two macroalgae and feeding rate were influenced by prev ious experience in the intertidal isopod Dynamene bidentata (Adams). I n preference experiments, animals reared in the laboratory with either Arcus vesiculosus L. or Cystoseira baccata (Gmelin) Silva as sole res ources did not exhibit preference for either of the two algae. Prefere nce for Fucus was exhibited by the same animals in a subsequent experi ment. Specimens reared on Cystoseira exhibited a greater feeding rate than those reared on Fucus. Animals collected in the field on Fucus an d Cystoseira preferred Fucus. Digestive efficiency was consistently hi gher when the animals ate Fucus than when the animals ate Cystoseira. Results suggest that, in D. bidentata, feeding preferences are set aft er the animals sample the environment for food quality. The existence of a compensatory mechanism in animals kept on suboptimal food resourc es (Cystoseira) is also suggested.