Dynamics of the benthic food web in St. Georges Bay, southern Gulf of St. Lawrence

In situ rates of oxygen uptake, carbon dioxide and inorganic nitrogen release from sediments at 34 m depth in St. Georges Bay, Nova Scotia (Canada) increased as temperature of bottom water increased between April and November. Rates of gas and nutrient exchange were linearly related to temperature and regressions were used to estimate daily rates of exchange between sediment and overlying water. Sedimentation of particulate organic carbon from the euphotic zone at depths above bottom which reduced collection of resuspended material was slightly less than carbon released by benthc aerobic respiration between April and November. Anaerobic microbial respiration corrected for aerobic oxygen uptake accounted for approximately 50 % of total carbon dioxide release. Nitrogen sedimentation from the euphotic zone exceeded regeneration of inorganic nitrogenous nutrients from sediments during periods of weak stratification but a balance existed when the water column was stratified. Total inorganic nitrogen release including N2 produced by denitrification was not measured but mineralization could have supplied approximately 20 % of phytoplankton requirements it nutrients released at the sediment were distributed homogeneously to the euphotic zone. Estimates of production by benthic macrofauna, calculated from biomass and assumed annual turnover ratios, equalled from 10 to 30 % of average particulate organic carbon sedimentation at 22 m for stratified and unstratified periods. Demersal fish production by a similar calculation amounted to from 1 to 7 % of estimated production of macrobenthos.