Inter-site differences in the biodynamics and body concentration of silver in a marine predatory gastropod

Abstract

The body concentrations of Ag in a top marine predator, the whelk Thais clavigera, varied significantly (1.10 to 4.67 µg g -1 dry wt) in individuals collected from 3 intertidal rocky shores in Hong Kong, whereas there was no significant difference in Ag concentrations in species from lower trophic levels (macroalgae Ulva sp. and rocky oyster Saccostrea cucullata). We compared the variation in Ag biodynamics in whelks collected from these 3 locations. There was no significant difference in the Ag dietary assimilation efficiency, Ag dissolved uptake rate, or estimated metallothionein concentration among the 3 locations. Significant differences were found in the Ag efflux rate constant and the subcellular distribution of Ag. Whelks from Clear Water Bay, which had the lowest body concentration of Ag, had a higher Ag efflux rate constant (0.0268 d ), as well as a correspondingly lower fraction of Ag in the metallothionein-like protein pool (which might contain both metallothioneins and other low molecular weight thiols). The Ag distribution in the other 4 subcellular fractions (metal-rich granules, cellular debris, organelles, heatsensitive proteins) was similar among the 3 sites. The biokinetic model demonstrated that biokinetic parameters can predict this 4-fold inter-site difference of body Ag concentrations in whelks. Moreover, such variation was mainly caused by variation in Ag efflux, although other parameters such as dietary assimilation and the concentration of Ag in prey were also important. Our calculations suggest that the prey composition may be specific to the site. The complexity of food webs should thus be considered when examining metal bioaccumulation in marine predators.