Marine Biology 27, 213-217 (1974) 9 by Springer-Verlag 1974 Survival and Chloride Ion Regulation of the Porcelain Crab Petrolisthes armatus Exposed to Mercury G. Roesij 1 adi_, S.R. Petrocelli I, J.W. Anderson I B.J. Presley 2 and R. Sims 2 IDepartment of Biology, Texas A&M University; College Station, Texas, USA, and 2 Department of Oceanography, Texas A&M University; College Station, Texas, USA Abstract Acute toxicity bioassays conducted at various salinities demonstrated that mercury (as mercuric chloride) at low concentrations was lethal to Petrolisthes armatus. Ninety-six hour LC50 values varied from 50 to 64 parts per billion (ppb) of mercury, depending on test salinities. Lower sa- linities decreased the time to death of mercury- exposed crabs. Differences in survival after 96 h due to salinity were not statistically significant. Blood chloride concentrations were regulated hyper- chloride to the medium at low salinities and hypo- chloride at high salinities by acclimated crabs. The salinity isochloride to blood was 22O/oo S. Transfer of crabs from 15~ S to salinities ranging from 7 to 35O/oo S resulted in new steady- state chloride levels within 12 h. Exposure to 50 ppb mercury did not alter chloride ion regulation of either acclimated crabs or crabs adjusting to new salinities. Introduction The presence of mercury in the environment is well documented, and the possibility of adverse effects on the biosphere has generated much concern (see Saha, 1972 for recent review). With respect to marine fauna, a recent bibliography (Eisler, 1973) suggested that the majority of studies have con- sidered either baseline residue levels of field- collected organisms or effects on survival. Rel- atively few studies have reported effects on physiology or interactions of mercury with other variables. Corner and Rigler (1958) and Vernberg and Vernberg (1972) studied uptake of mercury by aquatic organisms. Effects of interactions between mercury and other variables were investigated by Binet and Nicolle (1940), Portman (1968), and Vernberg and Vernberg (1972). Ballard and Oliff (1969) and Vernberg and Vernberg (1972) studied effects of mercury on respiration. Activity of anticholinesterase and liver enzymes in the presence of mercury was studied by Abou-Donia and Menzel (1967) and Jackim et al. (1970), respective- ly. Selected responses of larval crabs exposed to mercury were reported by De Coursey and Vernberg (1972) and Vernberg et al. (1973). The anomuran crab Petrolisthes armatus is widely distributed (Haig, 1956), often occurring in large numbers on oyster reefs of Texas (USA) bays. Ionic regulation of these euryhaline organisms has not been previously reported. Effects of mercury on survival in various salinities and on chloride ion regulation of Petro- listhes armatus are reported here. Since chloride ions account for approximately 90% of the total anionic concentration of crustacean blood (Prosser, 1973), it was thought that regulation of blood chloride levels by these crabs might prove to be a sensitive parameter by which a sublethal effect of mercury could be assessed. Materials and Methods Petrolisthes armatus used in this study were collected in East Matagorda Bay, Texas (USA) during the summer of 1973. Environmental temperatures and salinities at times of collection varied from 28 ~ to 35~ and 12 to 15~ S, respectively. Crabs were maintained at the laboratory in continuously filtered seawater (prepared with Instant Ocean Synthetic Sea Salts) of 15O/oo S and at room tem- perature (20 ~ to 22~ Desired salinities were obtained by diluting 35O/oo S Instant Ocean with distilled water. Crabs were fed ground Tetramin, a commercial fish food. All experiments were con- ducted at room temperature. Crabs were held under these conditions for I to 2 weeks prior to ex- perimentation. Effect on Survival Acute toxicity bioassays were conducted as sug- gested in A.P.H.A. (1971). Mercury concentrations tested were I, 25, 50 and 75 ppb, since preliminary bioassays showed that 96-h LC50 values varied from 25 to 75 ppb. Bioassays were conducted at 7, 14, 21, 28 and 35~ S, since this range of salinities was found to be within the tolerance limits of Petrolisthes armatus. Glass aquaria containing 5 1 of aerated water under static conditions were used for exposures. LC50 values were determined by graphic interpolation (A.P.H.A., 1971). Two-way analysis of variance was also used to analyze survival data.