Structure and function assessment of macrobenthic communities from north of the Dogger Bank, the Oyster Ground and at Sean Gas Field, in 2007

Four infaunal replicate samples were collected at each site using 0.1 m2 Nioz corers (diameter of approximately 30 cm) were sieved on a 1mm mesh sieve, the sieve remains were then sorted and preserved following the methodology described by Boyd (2002). On return, to the laboratory all the infaunal samples were identified to the lowest taxonomic level as possible, counted and weighted. Five epifaunal replicate samples were collected at each site using 2 m beam trawls during each of the five research cruises. Each trawl was conducted at a constant speed (~2 knots per minute) and sampled an area of seabed of approximately 400 m2. Once on board, the contents of the trawl were sieved over 5mm mesh and all retained individuals were identified, counted and weighed. In some cases, the very high numbers of some groups (e.g. brittle stars, shrimps, and small fish) needed sub-sampling before counting and weighting. The raw abundance and biomass data for both the infauna (from the cores) and epifauna (trawls) were scaled to values per m2. As some taxa were present in both datasets, taxa which were more appropriately classed as infauna and/or their densities were better estimated via a corer were classed as infauna and removed from the trawl data. Accordingly, those taxa which were generally considered as epifaunal (and their numbers and biomasses better estimated using a trawl) were considered as epifaunal and/or their densities more suitably estimated using a trawl were reported as epifauna.