Role of filtering and biodeposition by Adamussium colbecki in circulation of organic matter in Terra Nova Bay (Ross Sea, Antarctica)

At Terra Nova Bay, the scallop Adamussium colbecki (Smith, 1902) characteri ses the soft and hard bottoms from 20 to 80 m depth, constituting large bed s and reaching high values of density (50-60 individuals/m(2)) and biomass (120 g/m(2) DW soft tissues). To assess its role in the organic matter recy cling in the coastal ecosystem, its filtering and biodeposition rates were evaluated in laboratory experiments during the austral summer 1993/94. Filt ration rates, measured in a flow-through system, were calculated from the d ifference in particulate organic carbon (POC), nitrogen (PON) and chlorophy ll-a (Chl-a) concentration in inflow and outflow water. Experiments were pe rformed using natural sea water with POC, PON and Chl-a concentrations of a bout 450 mu g/l, 90 mu g/l and 2 mu g/l, respectively. The biodeposition ra te and the biochemical composition of the biodeposits were studied in order to detect how the organic matter is transformed through feeding activity o f A. colbecki. At + 1 degrees C temperature, the average filtering rate was about 11 h(-1) g(-1) (DW soft tissues) in specimens ranging in body mass f rom 2 to 3 g (DW soft tissues) and 6-7 cm long. The biodeposition rate in 3 -8 cm long specimens, ranging from 0.4 to 5.7 g (DW soft tissues), was abou t 5.65 mg DW/g DW/day, leading to an estimate of Corg flux, through biodepo sition by A. colbecki, of about 21 mg C m(-2) day(-1) at in situ conditions . Comparison between the biochemical composition of seston and biodeposits shows a decrease of the labile compounds, of the Chl-a/phaeopigments ratio in the biodeposits. The recorded C/N ratio decrease suggests a microbial co lonisation in the biodeposits. This study suggests that Adamussium colbecki plays an important role in coupling the material fluxes from the water col umn to the sea bed, processing about 14% of total Carbon Bur from the water column to the sediments, with an assimilation efficiency of 36%.