GROWTH VARIATIONS IN ARCTICA ISLANDICA L (MOLLUSCA) - A REFLECTION OFHYDROGRAPHY-RELATED FOOD-SUPPLY

The growth lines in shells of Arctica islandica from the Fladen Ground have been used to construct long-term chronologies of growth variatio ns. Individual specimens showed characteristic sequences of periods in high and low growth rates. Because the deviations were strongly synch ronized, an environmental factor is held responsible. Inter-annual var iations in either temperature or phytoplankton abundance could not exp lain the observed variations. The hypothesis is therefore put forward that the occurrence of dense patches of Arctica and the variations in growth result from variations in import and accumulation of organic ma tter by an eddy system overlying the area. Evidence for this hypothesi s is provided by the correlation between the estimated inter-annual in flux of Atlantic water into the North Sea and the observed growth vari ations. (C) 1996 International Council for the Exploration of the Sea