Extremely rapid withdrawal behaviour of the sea pen Protoptilum cf. carpenteri in the deep Mediterranean

Abstract

Sea pens (Octocorallia, Pennatulacea) are a specialized and morphologically distinct group of octocorals. The majority of them have adapted to survive on soft sediments with the help of an anchoring muscular peduncle. The whip-like sea pen Protoptilum carpenteri is considered a deep-sea North Atlantic species, which recently has been documented also in the Mediterranean Sea, where its actual distribution and abundance are still unknown. Even less is known about its ecology and behaviour, its reactions after disturbance, and its possible escape strategies. Several species of pennatulaceans can withdraw partially or completely into the sediment, following an apparent rhythmic but unsynchronized procedure that is usually preceded by the closure of the autozooids and the expulsion of the water contained within the colony. The present study reports and discusses for the first time the extremely fast withdrawal behaviour of P. cf. carpenteri after in situ disturbance