Deep-Sea Research I 48 (2001) 217 } 236 Patterns in polychaete abundance and diversity from the Madeira Abyssal Plain, northeast Atlantic Adrian Glover*, Gordon Paterson, Brian Bett, John Gage, Myriam Sibuet, Martin Sheader, Lawrence Hawkins Zoology Department, The Natural History Museum, Cromwell Road, London SW7 5BD, UK DEEPSEAS Group, George Deacon Division, Southampton Oceanography Centre, Waterfront Campus, European Way, Southampton SO14 3ZH, UK Scottish Association for Marine Research, Dunstawnage Marine Laboratory, P.O. Box 4, Oban PA34 4AD, UK De & partement Environnement Profond, Centre de Brest de l'IFREMER, BP 70, 29280 Plouzane & , France Southampton Oceanography Centre, School of Ocean and Earth Science, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK Received 21 September 1999; accepted 9 February 2000 Abstract Polychaete abundance and diversity patterns from the Madeira Abyssal Plain (MAP) were studied together with data from three other sites on the northeastern Atlantic abyssal plains. Polychaete abundance at MAP was signi"cantly lower than at any of the other sites, including those lying under comparable productivity regimes. Analysis of diversity, using rarefaction and species counts per unit area, suggests that MAP is extremely species poor and shows dominance by a few common species. The MAP site is characterised by a super"cial layer of turbidite sediment, and the hypothesis is put forward that the unusual sediment characteristics at MAP have a!ected macrofaunal abundance over a vast area ('2000 km). Analysis of species composition indicates that the MAP site is not faunistically unique; rather it contains a high proportion of widespread, abundant, cosmopolitan species. We suggest that these are the opportunists of the abyssal benthic habitat. Di!erences in abundance between the other abyssal sites are the result of both productivity and local environmental conditions. Equitability at the other north Atlantic sites is not a!ected by productivity, although the actual number of species per unit area is a!ected, showing a south}north gradient.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Deep sea; Polychaeta; Productivity; Turbidite; Biodiversity; Biogeography; Northeast Atlantic; Madeira Abyssal Plain * Corresponding author. Tel.: 44-020-7942-5056; fax: 44-020-7942-5433. E-mail address: a.glover@nhm.ac.uk (A. Glover). 0967-0637/01/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 - 0 6 3 7 ( 0 0 ) 0 0 0 5 3 - 4