Bioindicative potential of shell abnormalities occurring in the clam Macoma balthica (L.) from the Baltic Sea

► We studied shell deformities (SD) in Macoma balthica from the Baltic Sea. ► SD included damages of the dorsal margin visible as shell excavations, destruction of the beak, umbo and hinge ligament, decrease in the shell' thickness and transparency. ► Clams with SD were characterized by increased frequency of MN and decreased BMI. ► SD occurred more often in polluted areas (TBT and copper) but no clear causal factor was established. ► We conclude that SD can be a good non-specific, cost effective and easy to use biomarker for environmental monitoring.