In situ observations on withdrawal behaviour of the sea pen Virgularia mirabilis

Abstract

Sessile marine organisms respond to environmental disturbance and predation by means of different adaptive strategies. Sea pens (Octocorallia, Pennatulacea) are colonial cnidarians adapted to survive on the muddy and sandy bottoms of the continental shelf and slope. Some of them can withdraw partially or completely into the sediment on an apparent rhythmic but unsynchronized procedure (Langton et al. 1990). Withdrawal into the sand or mud by sea pens tend to be preceded by the closure of the polyps and the expulsion of the water contained within the colony (Hoare and Wilson 1977). Only a few contractions are generally sufficient for the animal to hide into the mud and some colonies can withdraw into the sediment within few seconds if disturbed