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)

Laetitia M Gunton,Andrew J Gooday,Adrian G Glover,Brian J Bett

doi:10.1016/j.dsr.2014.11.010

Laetitia M Gunton, Andrew J Gooday + Show 2 more

Open Access

https://doi.org/10.1016/j.dsr.2014.11.010

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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 ~3500m. Abundance (macrobenthos sensu stricto, >300μm) varied significantly (p<0.001) among sites, and decreased from east to west; highest in the Eastern branch (6249±standard deviation 1363ind.m−2) and lowest on the slope (2744±SD 269ind.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

Submarine canyons are major topographic features on continental margins
The present study investigates these faunal parameters at the higher taxon level for the macrofauna as a whole, and at the family level for the dominant macrofaunal group at the same water depth within different branches of the Whittard Canyon and on the adjacent slope
Bathymetry and derivatives The slope angle of the seafloor at sites sampled inside the canyon branches was fairly uniform, ranging from means of 2.361 (Western branch) to 3.271 (Eastern branch) (Table 1)

Summary

Introduction

Submarine canyons are major topographic features on continental margins. They play an important role as fast-track conduits for the transport of material from the shelf to abyssal depths (Vetter and Dayton, 1998). Topography (Shepard and Dill, 1966) and proximity to a fluvial source will influence the disturbance regime. They have been known for over a century and a half (Dana, 1863), the rugged topography of canyons and the difficulty of sampling within them have limited multidisciplinary studies to the last 20 years (Ramirez-Llodra et al, 2010b). Current knowledge of canyon benthic biology is poor

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