Sperm morphology in the marine gastropodArchitectonica perspectiva (Mollusca): Unique features and systematic relevance

The marine amphipodAllorchestes compressa Dana, fed on the seagrassHeterozostera tasmanica, was exposed to sublethal concentrations of Cd, Cr, Cu and Zn for 4 wk in flowing sea water, and the concentrations producing the minimum detectable decreases (the minimum effect concentrations, MECs) in average weight, survival and biomass (average weight × survival proportion) were estimated by interpolation from regression models. Survival and biomass were more sensitive than average weight as indicators of sublethal effects. The lowest values of MEC for Cd, Cr, Cu and Zn were 11, >250, 3.7 and 99µg 1^–1, respectively. For Cu, this value fell below the minimum risk concentration (MRC) calculated from acute toxicity tests (LC₅₀) and application factors (AF); for Cd, the MEC was similar to the MRC; for Cr and Zn, the MECs were well above the MRCs. The metal concentrations in the amphipods at the MECs were 46, >46, 364 and 139µg g^–1 dry wt for Cd, Cr, Cu and Zn, respectively. Accumulation of the nutrient metals (Cr, Cu and Zn) showed some evidence of metabolic regulation, but the non-nutrient Cd was accumulated without regulation until the amphipods died. In general, those metals that were more highly accumulated by the amphipods were the more toxic.