Macrofaunal abundance and community composition at lower bathyal depths in different branches of the Whittard Canyon and on the adjacent slope (3500 m; NE Atlantic). (March 2015)

• Record Type: Journal Article
• Authors: Gunton, Laetitia M.; Gooday, Andrew J.; Glover, Adrian G.; Bett, Brian J.
• Is Part Of: Deep sea research. Volume 97(2015)
• Page Start: 29
• Page End: 39
• Publication Date: 2015-03
• Subjects: Whittard Canyon -- Submarine canyons -- Deep sea -- Macrobenthos -- Polychaetes; Oceanography -- Periodicals; Océanographie -- Périodiques; 551.4605
• DOI: 10.1016/j.dsr.2014.11.010
• Languages: English
• ISSNs: 0967-0637

Abstract

Abstract: We studied benthic macrofaunal abundance and community composition in replicate Megacorer samples obtained from three sites in different branches of the Whittard Canyon (NE Atlantic) and one site on the adjacent slope to the west of the canyon system. All sites were located at a depth of ~3500 m. Abundance (macrobenthos sensu stricto, >300 μm) varied significantly ( p <0.001) among sites, and decreased from east to west; highest in the Eastern branch (6249±standard deviation 1363 ind. m −2 ) and lowest on the slope (2744±SD 269 ind. m −2 ). Polychaetes were the dominant taxon, making up 53% of the macrofauna, followed by isopods (11%), tanaids (10%), bivalves (7%) and sipunculans (7%). Among the polychaetes, the Amphinomidae was the dominant family (27%), followed by the Spionidae (22%). Assemblage composition changed across the sites. From east to west, the proportion of polychaetes and isopods decreased (by 6% in each case), while sipunculans and tanaids increased (by 13% and 8%, respectively). The ranking of the two dominant polychaete families reversed from east to west (Eastern branch—Amphinomidae 36%, Spionidae 21%; Slope—Spionidae 30%, Amphinomidae 10%). Ordination of faunal groups (macrofaunal higher taxa, and polychaete families) revealed that the Central and Eastern branches were substantially similar, while the Western branch and slope sites were relatively distinct. A very similar pattern was evident in a corresponding ordination of environmental variables across the sites. An analysis of faunal similarities (ANOSIM) indicated that the Western branch/slope and Central branch/Eastern branch groups displayed the highest similarity. The clearest separation was between the slope and the Eastern branch. We conclude that, when compared at the same water depth, macrofaunal abundance and composition varies between open slope and canyon location, as well as among canyon branches. These differences probably reflect the influence of organic enrichment together with hydrodynamic activity, both of which are influenced by the topographic profile of individual canyon branches. Highlights: Megacore samples were collected in a canyon and on the adjacent slope at 3500 m. Macrofaunal abundance was higher inside the canyon compared with the slope site. Abundance in the three canyon branches decreased from east to west. Macrofaunal and polychaete assemblage composition changed across sites. Differences between branch sites were as great as between canyon and slope sites.