Cd and Se aqueous uptake and exposure of green mussels Perna viridis : influences of seston quantity

Trace metals are available to marine bivalves through uptake from both the aqueous and dietary phases. In this study, I sought to determine if there is any interaction between these 2 exposure pathways. The uptake of Cd and Se by green mussels Perna viridis from the aqueous phase was measured at different phytoplankton concentrations (green alga Chlorella autotrophica). Controlled experiments were performed to ensure that, in the presence of algal particles, the majority of metal accumulation by the green mussels was due to uptake from the aqueous phase. The influx rate of metals was independent of the food concentration and the clearance rate of the mussels, indicating that metal uptake from the aqueous phase was not directly related to the food concentration. These results verify the assumption that metal uptake from different exposure pathways is additive and that there is no direct interaction between different routes of exposure. Metal uptake by green mussels was further tested after exposing the mussels to neurotransmitters (serotonin which stimulates ciliary pumping and dopamine which inhibits ciliary pumping). Complete inhibition of ciliary pumping was reached after addition of 100 μM of dopamine. Despite changes in the pumping activity due to exposure to neurotransmitters, there was no evidence showing the reduction or enhancement of metal uptake. A bioenergetic-based kinetic model was then employed to model the influence of seston quantity on the exposure pathways of metals in the mussels. Our calculations indicated that the seston quantity substantially influences the relative importance of aqueous versus dietary exposure, primarily due to the dependence of a green mussel’s ingestion activity on seston quantity. At a higher seston concentration, the exposure pathways are not influenced by the change in seston concentration due to the maintenance of a maximum ingestion rate and pseudofeces production.