Morphological differences in Macoma balthica (Bivalvia, Tellinacea) from aDutch and three southeastern United States estuaries

Field collections of the bivalve Macoma balthica in the Dutch Wadden Sea an d three southeastern United States estuaries revealed morphological differe nces between populations of the two sides of the Atlantic Ocean. Individual s of the same age showed much larger shell lengths at the American stations . In addition, bivalves of the same body weight had higher siphon weights a t the American stations than at the Dutch stations. This difference in siph on size was related to their burying depths. The American population, which invested more in heavier siphons, was able to burrow much deeper into the sediment (up to 30 cm). Deep burial may be an adaptation to avoid exposure to the high southern temperatures. Furthermore, it may serve as a refuge fr om blue crab predation. The results of our comparison between the southern American population and the European support the suggestion that population s of M. balthica living in these two regions should be considered separate and sibling species. (C) 1999 Elsevier Science B.V. All rights reserved.