Differential uptake of dissolved and particulate organic carbon by the marine mussel Perna viridis

We used radiotracers in laboratory experiments to determine the organic carbon uptake by the marine mussel Perna viridis from different diets (phytoplankton and detritus) and from the dissolved phase (colloidal and low molecular weight organic carbon). Standard compounds (glucose, arginine, and leucine, and the carbohydrate macromolecular dextran with sizes ranging from 3-2,000 kDa) were used to study organic matter flux into the green mussels. Carbon absorption was significantly affected by the food type and quality. The highest absorption efficiency (AE, 80%) was from the diatom Thalassiosira pseudonana, while the AE from Chlorella autotrophica was comparable with those from three types of algal detritus (20-30%). Mussels were able to directly ingest macromolecular dextran colloidal materials. Significant accumulation of these compounds was found both in the gills and the digestive glands of the mussels within the 12-17-h exposure period. Similarly, a significant accumulation of biogenic colloidal organic carbon (COC) and low molecular weight ultrafiltered organic carbon (UOC) was found. Uptake of UOC and COC resulting from the decomposition of different algal sources was comparable, with an uptake rate constant of 6.08 X 10(-4) L g(-1) dry wt h(-1) and an absorption efficiency of 0.0053%. A kinetic model was subsequently applied to quantitatively evaluate the carbon contribution from dissolved and particulate sources to general organic carbon uptake by the mussels. Mussels accumulated organic carbon predominantly from the particulate phase, with very little (<0.2%) coming from the DOC. However, the apparent ingestion and accumulation of colloids suggest that they can actively participate in the food chain dynamics in marine systems.