Abstract
The reactions of the sea urchins E. acutus and E. esculentus to Laminaria digitata and L. saccharina with or without the encrusting bryozoan Membranipora membranacea were tested in feeding- and Y-maze experiments. The 2 sea urchin species had almost identical responses to the food items offered, and they preferred to eat L. saccharina encrusted with Membranipora. In their search for food the sea urchins show the strongest attraction to the unencrusted alga. The ecological implications of these seemingly contradictory preferences are discussed.