Latitudinal variation in linear growth and other shell characteristics of Macoma balthica

Shells of the bivalve Macoma balthica (L.) were studied from locations throughout its geographic range on both sides of the North Atlantic. These observations were supplemented by records from the literature. North-south clines were detected in shell coloration, relative shell dimensions and shell growth parameters. Moreover, shells from the two sides of the Atlantic were so different (particularly in the south) that these populations can hardly be regarded as conspecific. It is, therefore, argued that latitudinal changes should be studied separately for the American and European populations. In America, growth rates increased continuously to the south, whereas in Europe maximal growth was observed at more intermediate latitudes.Virginia Institute of Marine Science Contribution No. 1251