The effect of salinity change on the heart rate of Mytilus edulis specimens from different ecological zones

The heart rate of specimens of Mytilus edulis (L.) both from the sublittoral and littoral zones exposed to normal and altered salinity was investigated in a long-term experiment. The heart rate was monitored by a non-invasive method for nine days. The heart rate of sublittoral mussels was higher than that of littoral ones. This suggests a higher level of metabolic activity in sublittoral mussels. When exposed to moderate hyposalinity (15 g l−1) M. edulis from both zones showed a significant decrease in the heart rate with respect to the control salinity (25 g l−1), but sublittoral mussels had a more prominent bradycardia. The heart beat quickly accelerated in all organisms when they were returned to the control salinity medium. Throughout the experiment, heart contractions halted with distinct periodicity in all mussels.