Cd transfer in the deposit-feeder Prosobranch Hydrobia ulvae (Pennant) from benthic diatoms: the kinetics of rapid Cd assimilation and efflux

Abstract

The kinetics of Cd trophic transfer from benthic diatoms to the Prosobranch mud snail Hydrobia ulvae was described experimentally in microcosms using Cd contaminated microalgae (0.71, 3.63 and 8.54 μg Cd mg Chl a −1). The depurated mud snails (2 ind. cm −2) were allowed to feed on the stable Cd pre-contaminated benthic diatoms at the concentration of 2 mg Chl a dm −3 to ensure that the algal food availability was not a limiting factor. Weight-specific ingestion rate (IR) and assimilation efficiency (AE) were calculated by an indirect mass-balance method on the basis of metal residues in the snail tissues, and metal loss (efflux rate, Δ e) was estimated for the time intervals when a decrease or no change in the tissue metal concentrations occurred. A similar pattern of consumption was observed in all experiments: ingestion was rapid over the first 4 h, followed by slower ingestion period (between 4 and 16 h). The feeding behaviour of H. ulvae was not affected by the different diatom Cd concentrations. An analogous two-phasic pattern was observed in the tissue Cd concentration changes. Net accumulation of Cd in the snails was observed for the two highest exposures, indicating that the Cd threshold concentration in food above which metal is retained in the body, lies between 0.71 and 3.63 μg Cd mg Chl a −1. The respective 16-h AEs were 0.024% and 0.004% potentially due to rapid gut-passage of microalgae and/or diminished nutritional value of the food. The efflux rates, calculated for the last 12 h of exposure, were positively related to the concentration of Cd in the snail tissues and microalgae. This study demonstrated that trophic transfer should be considered as a source of Cd accumulation in snails and the ability of H. ulvae to enhance their rate of Cd elimination in response to elevated metal concentrations in the ambient environment is relevant for models predicting metal bioaccumulation and toxicity in coastal and estuarine systems.