RESPONSE OF THE AMPHIPOD DIPOREIA SPP - TO VARIOUS STRESSORS - CADMIUM, SALINITY, AND TEMPERATURE

The tolerance of the amphipod Diporeia spp. (formerly Pontoporeia hoyi) to salinity and temperature and the acute toxicity of cadmium were determined by laboratory tests. No mortality occurred during 28 d exposure at a salinity of 20 g sea salt L-1. Slower swimming and mortality occurred when the salinity was increased to 25 g sea salt L-1. In freshwater, Diporeia tolerate a temperature of 26-degrees-C but exhibit 82% mortality within 24 h at 28-degrees-C. Thus, Diporeia collected from southern Lake Michigan demonstrate a significant salinity and thermal tolerance. Sensitivity to cadmium depends on both the temperature and the salinity of the exposure solution. At 4-degrees-C in fresh water, the 96 h LC50 for Cd, administered as CdCl2, was 0.78 mg Cd.L-1 (95% CL 0.40-1.02 mg Cd.L-1). At 15-degrees-C, it decreased to 0.065 mg Cd.L-1(95% CL 0.051-0.074 mg Cd.L-1). In salt water, the tolerance to Cd at 4-degrees-C [96 h LC50 of 49.4 mg Cd.L-1 (95% C.L 45.3-52.7 mg Cd.L-1)] was much greater than in fresh water and decreased with increasing temperature, 96 h LC.50 of 6.02 mg Cd.L-1 (95% C.I 6.02-7.32 mg Cd.L-1) at 15-degrees-C. Overall sensitivity to cadmium increases with increasing temperature and decreases with increasing salinity within the salinity tolerance of the organism. Diporeia are important Great Lakes benthos exposed to a wide range of contaminants. While Diporeia's sensitivity to contaminants has been implied, this work provides supportive data on the sensitivity of Diporeia to selected stressors.