The Population Structure and Ecology of the Antarctic Scallop Adamussium colbecki in Terra Nova Bay

Abstract

In Terra Nova Bay, the scallop Adamussium colbecki (Mollusca Bivalvia) constitutes large beds up to 70–80m in depth, reaching high values of density (50–60 ind m⁻²) and biomass (120 g m⁻² DW soft tissues). Its population structure and biometrics have been studied during the summer of 1989/90, 1993/94, 1994/95 and 1995/96. The population of A. colbecki was studied in terms of abundance values and of size frequency distribution (modal length class: 70–75 mm). The growth rate of this species was assessed by X-ray methods and averaged 8 mm year⁻¹. Biometrical measures were performed in order to assess the influence of the summer increase in food supply on the life cycle of the scallop, showing a strong coupling between food supply and gonad development. On the basis of the gonadosomatic index values (GSI) and of the occurrence of planktonic larvae some speculations are made on the reproductive behaviour of this scallop.

In situ video recordings allowed the analysis of the swimming behaviour of Adamussium, providing evidence of the role of such behaviour as an escape reaction to predators.

Laboratory experiments were carried out in order to assess filtering and biodeposition rates, averaging, at +1 °C temperature, 11 h⁻¹ g⁻¹ (DW soft tissues) and 5–6 mg DWg DW⁻¹ day⁻¹, respectively. This allowed estimation of the C_org flux, through biodeposition by A. colbecki, which is about 21 mg Cm⁻² day⁻¹ under in situ conditions. On the basis of organic matter flux and laboratory estimates of Adamussium feeding activity, it was possible to assess the important role of the scallop in coupling the energy flux from the water column to the sea bed, processing about 14% of total carbon flux from the water column to the sediments, with an assimilation efficiency of 36%.