Heart beat rate of invasive Brachidontes pharaonis with respect to the native Mytilaster minimus within the Mediterranean Sea at varying salinites

Changes in heart beat rates (HBR) of Brachidontes pharaonis (an invasive Lessepsian species) and Mytilaster minimus (a native Mediterranean species) in response to changes in salinity values from brackish (20) to extreme hyper-saline (75) were investigated both in situ and in the laboratory. The two species displayed different responses to varying salinity, with clear differences in HBR observed between groups investigated at different salinities and between groups originating from different environments. The native species, adapted to narrow salinity changes as those observed in the superficial waters of the Mediterranean Sea, showed signs of stress at salinities slightly above 37 (in the range 37–45). On the other hand, the invasive species displayed clear signs of stress only at salinities over 45 and exhibited heart activity even under hyper-saline conditions (i.e. salinity = 75). These results indicate that the Lessepsian species has the potential to invade most of the transitional environments across the entire Mediterranean basin. We therefore stress the need of including Brachidontes pharaonis in all coastal monitoring programmes assessing the actual and potential spreading of alien species in the Mediterranean region.