The growth of the ocean quahog Arctica islandica L. was investigated with data from two sites of Kiel Bay, Western Baltic. At the experimental site "Benthosgarten" (BG), length-increment data were obtained from a colonization experiment and from implanted and resampled clams. At the "Millionenviertel" site (MV), clams were caught by dredging. Length-increment data were obtained from annual growth bands formed at the surface of the shell. A Von Bertalanffy growth function was fitted to both data sets. Growth at the BG site (K = 0.35, L∞ = 60.6 mm) was different from that at the MV site (K = 0.07, L∞ = 93.6 mm). The BG site growth parameters are assumed to be strongly biased due to the experimental set-up. Growth of the MV site population is similar to Atlantic populations of A. islandica but maximum age and length are much smaller in Kiel Bay. The annual P B ̄ ratio of the MV site population was estimated to be 0.34, which results in an annual production of 15 g AFDW · m -2 in this particular area. Total annual production in Kiel Bay is estimated at ≈ 11000 t AFDW, ≈40% of the estimated annual benthic community production. A. islandica is eaten mainly by cod Gadus morhua. During 1970-1985, ≈40% of the annual production of cod in Kiel Bay is estimated to have depended on this clam. © 1990.