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This study discusses the occurrence of neoplasia in the Baltic clam Macoma balthica from the Gulf of Gdańsk in recent years and investigates potential relationships between toxic compounds in the environment and the presence of the cancer. The disease was identified at four sampling stations during 1999–2002. Comparison with previous results highlighted the substantial prevalence of the tumour between 1998 and 2002. The prevalence of the cancer was strongly dependent on the sampling location (p < 0.001): it was highest at sampling point H45 (the deepest part of the gulf) and lowest at station PB30 (central part of the gulf). Monthly studies showed a trend towards an increasing prevalence of neoplasia during the warm months. However, over several sampling months no strong statistical correlation between the prevalence of the disease and the sampling time was found. The results of the study suggest that several environmental factors may promote the progress of the cancer in M. balthica from the Gulf of Gdańsk: it is most probably an indirect effect of pollution, although causality cannot be proven at this stage. Seriously polluted and exhibiting a considerable asymmetry of contamination, the ecosystem of the gulf provides an ideal environment for testing potential cause-effect relationships between pollutants and their biological effects.
The populations of common Baltic bivalves Macoma balthica, Mytilus edulis and Cerastoderma glaucum were studied in the Polish coast (up to 4 Nm), both in estuary and open coastal zones of the Middle Pomerania as well as in the Puck Bay and the Gulf of Gdańsk (up to 2 Nm). The following parameters were investigated: density of the bivalves and environmental conditions (distance from the shore, substrate type, coast type, depth). Relationships between environmental conditions and abundance of the consecutive bivalve species were analysed with the help of ordination method (redundancy analysis RDA) and multivariate regression trees (MRT). RDA analysis indicated that C. glaucum density depended mainly on the localisation along the coast while M. edulis occurrence was governed by the distance from the shore and depth. Only density of M. balthica depended evenly on all the environmental parameters. MRT analysis revealed that the main factors influencing the distribution of bivalves were sediment granularity and depth.
This study was designed to investigate seasonal and annual changes in the benthic macrofauna in relation to changes in hydrogen sulphide concentration in the sediment and the oxygen content in the water column. Data were collected over a three-year period from 1994 to 1997. The benthic macrofauna inhabiting the sediments of the Gulf of Gdańsk, in which H2S is permanently present, consists mostly of species with a high tolerance to oxygen deficiency and the presence of H2S. These species are: Macoma balthica, Harmothoe sarsi, Nereis diversicolor, Saduria entomon and Halicryptus spinulosus, as well as Pontoporeia femorata and Corophium volutator, which are more sensitive to these factors. In 1996–1997 a decline in the abundance of almost all benthic species, and especially of the bivalve M. balthica at all the stations was observed in comparison to 1994–1995.
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 Parseta, 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 (x¯ = 10.4 spec. m–2). Wet biomass of this bivalve ranged from 0 to 25.52 gww m-2 (x¯ = 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).
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