The role of native salinity regime on grass shrimp (Palaemonetes pugio) sensitivity to cadmium

In euryhaline crustaceans, sensitivity to toxic trace metals may be linked to osmoregulation and salinity conditions. This study investigated if grass shrimp (Palaemonetes pugio) populations from different salinity regimes differed in sensitivity to cadmium (Cd). Grass shrimp were collected in May 2011 from two marsh sites with average salinities of ~3.0 ppt and 24.0 ppt. Groups were acclimated for 3-32 weeks in either their respective native salinity (3.0 ppt → 3.0 ppt and 24.0 ppt → 24.0 ppt), or the average of the salinities of the two collection sites (3.0 ppt → 13.5 ppt and 24.0 ppt → 13.5 ppt). After acclimation, groups were exposed to equivalent free-ion Cd concentration (4.8 ± 0.3 mg/L, Cd(2+)) in their respective acclimated salinity to compare survival among salinity treatments. Results of Kaplan-Meier survival analysis indicated that 3.0 ppt → 3.0 ppt shrimp were more sensitive to Cd(2+) than any other group (p < 0.0001). Additionally, 3.0 ppt → 13.5 ppt shrimp were less sensitive to Cd(2+) than were 24.0 ppt → 13.5 ppt shrimp (p = 0.0013). These results suggest that sensitivity of grass shrimp to Cd is dependent upon the salinity during exposure, and the salinity regime from which the tested population originated. The implication is that toxicity studies and risk assessments using euryhaline crustaceans should consider the salinity of test population collection sites when interpreting and comparing results.