Long-term change in the megabenthos of the Porcupine Abyssal Plain (NE Atlantic)

A radical change in the abundance of invertebrate megafauna on the Porcupin e Abyssal Plain is reported over a period of 10 years (1989-1999). Actiniar ians, annelids, pycnogonids, tunicates, ophiuroids and holothurians increas ed significantly in abundance. However, there was no significant change in wet weight biomass. Two holothurian species, Amperima rosea and Ellipinion molle, increased in abundance by more than two orders of magnitude. Samples from the Porcupine Abyssal Plain over a longer period (1977-1999) show tha t prior to 1996 these holothurian species were always a minor component of the megafauna. From 1996 to 1999 A. rosea was abundant over a wide area of the Porcupine Abyssal Plain indicating that the phenomenon was not a locali sed event. Several dominant holothurian species show a distinct trend in de creasing body size over the study period. The changes in megafauna abundanc e may be related to environmental forcing (food supply) rather than to loca lised stochastic population variations. Inter-annual variability and long-t erm trends in organic matter supply to the seabed may be responsible for th e observed changes in abundance, species dominance and size distributions. (C) 2001 Elsevier Science Ltd. All rights reserved.