Effect of Hyposaline Stress on Metabolic Rate of the Invasive Mussel Mytilus galloprovincialis

Climate change is predicted to decrease ocean salinity as the polar ice caps melt and the occurrence of precipitation events increases. Decreased ocean salinity (hyposalinity) may negatively impact marine invertebrates, especially marine mussels, as they are osmoconformers and their internal osmolarity depends on the solute concentration of their environment. Hyposalinity stress may influence cell function and alter mussel physiology. To compensate for the change in the environment, mussels may expend more energy to restore internal osmolarity, which can be assessed by quantifying metabolic rate. Thus, the purpose of our research was to examine the physiological response of Mytilus galloprovincialis, an invasive mussel species in Southern California, to varying salinity conditions. Mussels (N=39 total) were collected from Marina Del Rey, CA and acclimated in tanks to control conditions (34 ppt, 18°C seawater). Following acclimation, mussels were placed in individual closed-system respirometers to measure their oxygen consumption under different salinity conditions (35, control; 28 and 25 ppt, hyposaline) and subsequently used to calculate metabolic rate (MO2 as mg O2/min/g wet weight). Mussels exposed to hyposalinity (28 and 25 ppt) showed a trend towards increasing metabolic rate relative to the controls, however these data were not statistically significant (1-Way ANOVA, P=0.0975). Our data suggests that exposure to hyposalinity may cause a physiological response in mussels, where energy may be used to restore internal osmolarity. Coastal marine organisms will experience hyposaline stress as climate change progresses and our data begins to suggest that this may require a greater energy output as seawater conditions change