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A population of Mya arenaria was studied in the Polish coastal zone (up to 3 nautical miles) of the Baltic Sea in the open coast of Polish Middle Pomerania. Abundance, wet biomass, and the frequency of Mya were determined in the coastal waters, including estuaries of the Parsęta, Wieprza, Słupia, Łupawa, and Łeba rivers and Władysławowo. The frequency (F) of Mya in the open coast of the Middle Pomerania amounted to 19.5%. The abundance of Mya, in the coastal zone surveyed, ranged from 0 to 265 specimens per m2 of the bottom (xˉ = 10.4 spec. m–2). Wet biomass of this bivalve ranged from 0 to 25.52 gww m-2 (xˉ = 1.56 gww m-2). Apparently Mya arenaria has found better conditions for living and development in the central of the Middle Pomerania coast. The abundance of this mollusc in the estuary of Słupia (Ustka) was 100-fold higher than in the estuary of Wieprza (Darłowo) and Łupawa (Rowy) and the wet weight was 11-fold higher, respectively. Mya arenaria plays an important role in the monitoring of benthos of the Baltic Sea, constitutes a food base of animals (fish), and takes part in the process of purification of waters of the coast stretch studied (biofiltration, biosedimentation).
Key words: Polish Baltic Sea coast, estuary, Mya arenaria, abundance and biomass