Trophic structure of macrobenthos in the Gulf of St. Lawrence and on the Scotian Shelf

The Gulf of St, Lawrence and Scotian Shelf provide a diversity of oceanogra phic conditions in a continental margin setting. Climate is markedly season al, and bathymetry and hydrodynamic conditions cover a broad range, signifi cantly influencing the patterns of organic matter sedimentation and, potent ially, benthic community dynamics, Samples for analysis of benthic macrofau na and sediment microorganisms were collected at six stations in the Gulf o f St. Lawrence (GSL) and the Scotian Shelf during winter and summer cruises , as part of the Canadian Joint Global Ocean Flux Study. Multivariate analy ses indicate significant site-related trends in trophic guilds, benthic ass emblages, and microbial activity, some of which are related to geomorpholog ical characteristics (bathymetry, topography, and substratum). Macrofaunal trophic guild data show that the stations with relatively deep settling bas ins (Cabot Strait and Emerald Basin), dominated by surface deposit feeders, were distinct from stations with sloping bottoms (Anticosti Gyre and Antic osti Channel), where subsurface deposit feeders dominated or surface and su bsurface deposit feeders were equally abundant. Deposit feeders (surface an d subsurface trophic groups) made up > 60% of the benthic communities, exce pt at the Scotian slope station where they represented 44% of the total ben thic abundances. Based on the data collected in both the water column and t he sediment at three deep stations in the GSL, we hypothesize that the prop ortion of surface and subsurface deposit feeders, and thus the nature of bi oturbation activity, is related to the magnitude and pattern of organic mat ter supply from the euphotic zone. (C) 1999 Elsevier Science Ltd. All right s reserved.