The aim of this project was to examine the trophic linkages between the invasive freshwater bivalve Corbicula fluminea and its pelagic and benthic food sources. C. fluminea can feed both from the water column (filter-feeding) and from the sediments (pedal-feeding). The relative importance of these two feeding modes is poorly understood, in particular with regard to the uptake of essential nutrients. By analyzing the biochemical (essential lipids) composition of potential planktonic and benthic food sources we investigated how essential nutrients are obtained. Experiments with marine bivalves suggest that the ability to synthesize long chain polyunsaturated fatty acids (PUFAs) and sterols de novo is generally low or absent among bivalve species, which implies that a dietary supply with these lipids is essential for growth and reproduction. We could show that somatic growth of clams is affected by the dietary supply with essential lipids (Basen et al. 2011) and that feeding on cyanobacterial food sources results in sterol-limited growth (Basen et al. 2012).

To assess the capability of clams to process and therewith modify the quality of pelagic food sources for subsequent use by benthic invertebrates, we conducted growth experiments in which juvenile Gammarus roeselii were raised either directly on sedimented pelagic autotrophs (algae, cyanobacteria) or on the same autotrophs biodeposited by clams either as feces or pseudofeces. We could show that growth and survival of G. roeselii are improved when autotrophs are offered as biodeposition material and suggested that this clam-mediated upgrading of food quality is due to both an increased bioavailability of pelagic food particles, which are packed in mucus during clam processing, and an increased dietary provisioning with essential lipids originating from the clams. We propose that filter-feeding bivalves provide a crucial link between the pelagic and benthic food web not only by deflecting energy fluxes, but also by processing and upgrading pelagic food for benthic invertebrates (Basen et al. 2013).

This project was part of the Collaborative Research Centre “Littoral of Lake Constance” (SFB 454).