Effect of salinity and temperature on feeding physiology and scope for growth of an invasive species (Brachidontes pharaonis - MOLLUSCA: BIVALVIA) within the Mediterranean Sea

The Indo-Pacific mytilid Brachidontes pharaonis (Bivalvia, Fischer 1870) offers an excellent model for the study of “Lessepsian migration” and the successive colonization at new Mediterranean locations. This species in out competing indigenous bivalves is particularly well adapted to Mediterranean conditions and this is likely due to biological characteristics and physio-ecological plasticity. In the present paper, we report on clearance rate (CR), respiration rate (RR) and Scope for Growth (SFG) of B. pharaonis collected from a Western Sicilian pond (Southern Tyrrhenian, MED). Physiological variables were determined in response to a range of temperatures from 11 ° to 20 °C and a broad range of salinities from 15 to 60 psu. Salinity and temperature had a significant influence on CR of B. pharaonis as therewas a general reduction in CR with a decline in temperature from 20 °C to 11 °C and declining salinity from 37 to 15 psu. RR showed a general temperature dependent relationship with highest RR at 20 °C. SFG showed negative values at lowest salinity of 15 psu at all tested temperatures. SFG values were generally the highest at 45 psu (at 11 °C and 20 °C), although SFG showed a maximum at 37 psu at 15 °C. SFG values were positive over the broadest range of salinities (25 to 60 psu) at 20 °C. The plasticity of the physiological rates demonstrated that B. pharaonis had the capacity to maintain positive SFG and tolerate a wide range of temperature/salinity conditions. Possible implications of high physiological plasticity of B. pharaonis in competing against indigenous bivalves are discussed.