The effect of salinity on survival,bioenergetics and predation risk in the mud crabs Panopeus simpsoni and Eurypanopeus depressus

The effect of salinity on survival, bioenergetics and predation risk was studied in two common mud crabs in the Gulf of Mexico, Eurypanopeus depressus and Panopeus simpsoni. Eurypanopeus survived better at low salinities (the 28-day LC₅₀ of E. depressus was 0.19 PSU compared with 6.97 PSU for P. simpsoni). While low salinity increased energy expenditure and reduced food consumption and absorption, resulting in lower scope for growth, identical responses to salinity occurred in both species. Both species also had similar salinity-dependent patterns of hyper-osmoregulation. Because these physiological mechanisms could not explain differences between the two species in salinity tolerance, we explored the effect of salinity on competition for refugia. Eurypanopeus had higher resource holding potential for refugia, especially at low salinity. As a consequence it had lower predation risk to blue crabs in laboratory experiments. The higher tolerance by E. depressus for low salinities, and greater resource holding potential for refugia may explain why it has a more euryhaline distribution than P. simpsoni.