Chromosomal study of spatial variation of the prevalence of a gill neoplasia in Macoma balthica (L.) from the Gulf of Gdansk (Baltic Sea)

Spatial variation of the prevalence of a gill neoplasia in the bivalve Maco ma balthica was investigated by chromosomal study of individuals from ten d ifferent sites in the Gulf of Gdansk. The prevalence of gill neoplasia, ind ividually identified by the occurrence of abnormal metaphases with higher c hromosome numbers than normal metaphases (2n = 38), ranges from 0 to 94% of individuals, according to the site studied. Sites Hel 45 m and Vistula 30 m, located in the zone of the thermocline and halocline were the most affec ted, probably related to very unstable hydrological conditions at these sit es. Out of a total of 152 animals studied from the Gulf of Gdansk, 33% show ed the occurrence of gill neoplasia. A chromosome number from 59 to 109 was scored in 29 abnormal metaphases. Karyotypes were constructed from 14 abno rmal metaphases and showed a similar general pattern. This study showed tha t chromosomal abnormalities involving numerical and morphological changes i mply similar disorders among the sites studied. Etiology of this disease is still unknown but the seriously polluted Gulf of Gdansk can be used as a m odel basin to assess the relationship between the incidence of neoplasia an d the possible controlling factors of environmental instability and/or leve l of environmental contaminants.