INCREASED SALINITY AFFECTS SURVIVAL AND OSMOTIC RESPONSE OF RUSTY CRAYFISH ORCONECTES RUSTICUS GIRARD, 1852 AND NORTHERN CLEARWATER CRAYFISH O-PROPINQUUS GIRARD, 1852 (DECAPODA: ASTACOIDEA: CAMBARIDAE) AS SALINITY INCREASES: THE POTENTIAL FOR ESTUARINE INVASIONS

摘要

The potential colonization of the rusty crayfish, Orconectes rusticus (Girard, 1852), has previously focused on lakes and streams of northeastern United States and southeastern Canada, but estuaries have not been considered. Rusty crayfish have recently been reported in tributaries of the Chesapeake Bay and the potential exists for crayfishes to invade and spread into the estuary. We determined survival, hemolymph osmotic pressure, and identified possible mechanisms of osmoregulation of the invasive O. rusticus and northern clearwater crayfish, Orconectes propinquus (Girard, 1852), in salinities of 0.5, 5, 15, and 30 ppt. Survival of both crayfishes (>83%) was unaffected at salinities of up to 15 ppt but declined significantly at 30 ppt to 17% for O. rusticus (P < 0.05) and 50% for O. propinquus (P > 0.05). Hemolymph osmotic pressure in both species was higher than the external medium up to 15 ppt, and then became nearly isosmotic with salinities at 30 ppt with a significant species by treatment interaction (F-3,F-55 = 4.4627, P = 0.0071). The primary osmoregulatory mechanisms in crayfishes involve ions (Na+ and Cl-) and free amino acids (FAAs) in muscle tissues. Concentrations of Na+ and Cl increased with increasing salinity in both species and accounted for 74-91% of the total hemolymph osmotic pressure with a significant species (Pillai's Trace = 0.9565, P < 0.0001) and treatment effect (Pillai's Trace = 0.23189, P < 0.0001). FAA concentrations in hemolymph remained low (1-4 mM) and did not differ significantly with increased salinity (P > 0.05). FAA in tail muscle tissue increased significantly with increasing salinity with a significant species by treatment interaction (F-3,F-20 = 5.1911, P = 0.0082). Both O. rusticus and O. propinquus were active in salinities of up to 15 ppt and were able to osmoregulate. Based on these laboratory experiments, the potential exists for both of these species to spread through large areas of estuaries into new rivers potentially threatening previously isolated watersheds.