Defensive behaviour of sea anemones in response to predation by the opisthobranch molluscAeolidia papillosa(L.)

Abstract

The defensive behaviour of 11 species of sea anemone when attacked by the nudibranchAeolidia papillosais described. An attempt is made to correlate their defensive responses with the habitat, and with the food preferences ofAeolidia. Actinia equinaresponds first by tentacle and column retraction, and then by inflation of the column, pedal locomotion, and detachment from the substrate.Anthopleura elegantissimaresponds in similar ways, butAnemonia sulcata, which has much longer tentacles, uses these in active defence against the eolid.Anemoniaalso crawls away but it does not detach.Actinia, AnthopleuraandAnemoniaare the preferred foods ofAeolidia. They commonly live in dense colonies where locomotion and detachment are likely to result in escape.Tealia felinais less preferred and is much less responsive when attacked byAeolidia.Anemones which possess acontia normally eject these when they are attacked byAeolidia. AlthoughAeolidiadoes occasionally eat acontian anemones, evidence is presented which suggests that acontia have some deterrent effect on this predator. Although most acontian anemones are probably able to move by pedal locomotion and to detach from the substrate, these responses are much less frequently given than byActinia equina.