How the green crab Carcinus maenas copes physiologically with a range of salinities.

To evaluate the physiological ability to adjust to environmental variations of salinity, Carcinus maenas were maintained in 10, 20, 32 (control), 40, and 50 ppt (13.8 ± 0.6 °C) for 7 days. Closed respirometry systems were used to evaluate oxygen consumption ([Formula: see text]), ammonia excretion (Jamm), urea-N excretion (Jurea-N) and diffusive water fluxes (with ³H₂O). Ions, osmolality, metabolites, and acid-base status were determined in the hemolymph and seawater, and transepithelial potential (TEP) was measured. At the lowest salinity, there were marked increases in [Formula: see text] and Jamm, greater reliance on N-containing fuels to support aerobic metabolism, and a state of internal metabolic alkalosis (increased [HCO₃^-]) despite lower seawater pH. At higher salinities, an activation of anaerobic metabolism and a state of metabolic acidosis (decreased [HCO₃^-] and increased [lactate]), in combination with respiratory compensation (decreased PCO₂), were detected. TEP became more negative with decreasing salinity. Osmoregulation and osmoconformation occurred at low and high salinities, respectively, with complex patterns in individual ions; hemolymph [Mg²⁺] was particularly well regulated at levels well below the external seawater at all salinities. Diffusive water flux rates increased at higher salinities. Our results show that C. maenas exhibits wide plasticity of physiological responses when acclimated to different salinities and tolerates substantial disturbances of physiological parameters, illustrating that this species is well adapted to invade and survive in diverse habitats.