Depth-related distribution and abundance of seastars (Echinodermata: Asteroidea) in the Porcupine Seabight and Porcupine Abyssal Plain, NE Atlantic

The depth-related distribution of seastar (Echinodermata: Asteroidea) species between 150 and 4950m in the Porcupine Seabight and Porcupine Abyssal Plain is described. 47 species of asteroid were identified from similar to14,000 individuals collected. The bathymetric range of each species is recorded. What are considered quantitative data, from an acoustically monitored epibenthic sledge and supplementary data from otter trawls, are used to display the relative abundance of individuals within their bathymetric range. Asteroid species are found to have very narrow centres of distribution in which they are abundant, despite much wider total adult depth ranges. Centres of distribution may be skewed. This might result from competition for resources or be related to the occurrence of favourable habitats at particular depths. The bathymetric distributions of the juveniles of some species extend outside the adult depth ranges. There is a distinct pattern of zonation with two major regions of faunal change and six distinct zones. An upper slope zone ranges from 150 to similar to 700 m depth, an upper bathyal zone between 700 and 1100 m, a mid-bathyal zone from 1100 to 1700 m and a lower bathyal zone between 1700 and 2500 m. Below 2500 m the lower continental slope and continental rise have a characteristic asteroid fauna. The abyssal zone starts at about 2800 m. Regions of major faunal change are identified at the boundaries of both upper and mid-bathyal zones and at the transition of bathyal to abyssal fauna. Diversity is greatest at similar to 1800 m, decreasing with depth to similar to 2600 m before increasing again to high levels at similar to 4700 m. (C) 2002 Elsevier Science Ltd. All rights reserved.