The trophic transfer of Cd, Cr, and Se in the barnacle Balanus amphitrite from planktonic food

We determined the assimilation efficiencies (AEs) and efflux rate constants of Cd, Cr, and Se in barnacles Balanus amphitrite feeding on diverse planktonic prey. The measured AEs of Cd, Cr, and Se for zooplankton prey (brine shrimp Artemia salina larvae and copepods Canthocalanus pauper and Temora turbinata) were 53 to 88, 32 to 59, and 63 to 76%, respectively, and for diatom diets were 35 to 86, 22 to 26, and 79%, respectively. Distribution of metals in the soft tissues of zooplankton could not account for the variability of AE for each metal, but did explain the variability of AE among different metals. Metal distribution in the cytoplasm of diatoms determined the variability of AEs among metals. There was a significant correlation between Cd and Zn in AE and efflux rate constant. No relationship in AE or efflux rate was found for the other metals. The efflux rate constants in B. amphitrite were 0.007, 0.020, and 0.014 d^-1 for Cd, Cr, and Se, respectively. Cd concentrations in barnacles, predicted by a simple bioenergetic-based kinetic model, were comparable to the actual concentrations measured in the field when phytoplankton was considered as the primary Cd source. Cd concentrations predicted by the model were much higher than the field measurements when copepods were assumed as the sole food source for barnacles. Trophic transfer appeared to be responsible for Cd accumulation in barnacles. Many biological and geochemical processes can affect metal accumulation in barnacles. Our study demonstrated that biological processes must be considered to interpret metal concentrations in barnacles when the barnacles are used to monitor coastal contamination.