Benthic polychaete diversity patterns and community structure in the Whittard canyon system and adjacent slope (NE Atlantic)

We examined deep-sea macrofaunal polychaete species assemblage composition, diversity and turnover in the Whittard Canyon system (NE Atlantic; 3500 m water depth). Replicate Megacore samples were collected from three of the canyon branches and one site on the continental slope to the west of the canyon, all at c. 3500 m water depth. A total of 110 polychaete species were recorded. Paramphinome jeffreysii was the most abundant species (2326 ind m-2) followed by Aurospio sp. B (646 ind m-2), Opheliidae sp. A (393 ind m-2), Prionospio sp. I (380 ind m-2), and Ophelina abranchiata (227 ind m-2). Species composition varied significantly across all sites. From west to east, the dominance of Paramphinome jeffreysii increased from 12.9 % on the slope to 39.6 % in the Eastern branch. Ordination of species composition revealed that the Central and Eastern branches were most similar, whereas the Western branch and slope sites were more distinct. High abundances of P. jeffreysii and Opheliidae sp. A characterised the Eastern branch of the canyon and may indicate an opportunistic response to a possible recent input of organic matter inside the canyon. Species diversity indices were higher on the slope than inside the canyon, and the slope site had higher species evenness. Within the canyon, species diversity between branches was broadly similar. Our data does not suggest that the Whittard Canyon makes a substantial contribution to the regional diversity of soft-bottom benthic polychaetes.