Survival and reproduction of Palaemonetes paludosus (Gibbes, 1850) (Decapoda : Palaemonidae) in saline water

In order to determine the effects of salinity on adult and larval survival, egg deposition, egg hatching, and metamorphosis, shrimp (Palaemonetes paludosus) were held in the laboratory and exposed to treatment salinities ranging from 0 to 35 ppt. Tests of adult survival indicate a 96 h LC5o between 30 and 35 ppt. Shrimp became ovigerous in salinities of 0-20 ppt (27?C), with ensuing egg hatching and metamorphosis limited to 0-5 ppt. Starved larvae hatched from field-caught ovigerous females in 0 ppt were able to metamorphose in salinities of 0-30 ppt; the 96 h LC50 for these larvae was between 30 and 35 ppt at temperature of 240C. These results suggest that P. paludosus can complete its life cycle in brackish water. The widely distributed grass shrimps of the genus Palaemonetes are ecologically important omnivores in estuarine and freshwater environments. They feed on algae, detritus, aquatic insects, crustaceans, and meiofauna (Bell and Coull, 1978) and, in turn, are eaten by fishes and other predators (Anderson, 1985; Beck and Cowell, 1975; Meehean, 1936; Swift, 1985; Welsh, 1975). Because of their ecology, grass shrimps are important for energy flow and turnover of detritus in the benthos and are an important energy link between benthic and pelagic organisms (Anderson, 1985; Welsh, 1975). Palaemonetes paludosus occurs in fresh waters of the coastal plain east of the Allegheny Mountains, from New Jersey to Florida (Beck and Cowell, 1975; Swift, 1985). It also occurs in Mississippi, Louisiana, and Texas, where, according to Beck and Cowell (1975), it probably has been introduced. Its introduction to California has been documented (St. Amant and Hulquist, 1969). Palaemonetes paludosus is generally regarded as a fresh-water species (Beck, 1980; Dobkin and Manning, 1964; Koehler, 1979; Turner et al., 1975), but it has been collected in water of 3.1 ppt in Louisiana by McGuire (1961) and in 0-10 ppt in Florida by Tabb and Manning (1961). Because the salinity of the water in which the shrimp were collected was variable and because ovigerous females or larvae were not observed, there is no conclusive evidence that P. paludosus is a permanent resident of brackish water in those studies. St. Amant and Hulquist (1969) collected adults, ovigerous females, and juvenile hrimp in waters with salinity of 25 ppt in Baja California. Afte the species was first reported from brackish water, osmoregulation studies were conducted in the laboratory (Dobkin and Manning, 1964; Turner et al., 1975). Anisosmotic extracellular regulation tends toward hypertonicity until 20 ppt, above which the regulation is switched to osmoconformity (Dobkin and Manning, 1964). Isosmotic intracellular regulation is a short-term response occurring until anisosmotic regulation is complete (Turner et al., 1975). Long-term effects of salinity were not determined by these osmoregulation studies. In the present study, acute and chronic salinity tolerance of P. paludosus was investigated to determine whether this species can reproduce in brackish water. There were four components of the investigation: (1) an acute test of salinity on adult survival, (2) a test to determine the effects of salinity on adult survival and egg deposition, (3) the testing of salinity on survival and metamorphosis of acclimated larvae hatched in saline water, and (4) the testing of salinity effects on survival and metamorphosis of unacclimated larvae hatched in fresh water. MATERIALS AND METHODS Specimens of Palaemonetes paludosus were collected during May by pushing a 5-m seine (2-mm mesh) through shallow weed beds along the banks of Stumpy Lake in Virginia Beach, Virginia. In the laboratory, shrimp were temperature-acclimated and transferred to holding tanks. They were held in the tanks for 2-3 weeks before experimentation. Photoperiod was set at 15 light: 9 dark using fluorescent bulbs. Room temperature was 24?C during the acute tests; then it was