Influence of food size and food quantity on the feeding of the mussel Dreissena polymorpha.

In common with many other suspension feeders, the freshwater mussel Dreissena polymorpha has a maximum filtration rate at low food concentrations and a maximum ingestion rate at high food concentrations. These high rates, which reflect the potential maximum food uptake of the animal, are called the filtration capacity and the ingestion capacity respectively. The ingestion capacity was attained without forming pseudofaeces with Chlamydomonas reinhardii as food. The incipient limiting level could be calculated as the quotient of these two values. A decrease of the filtration rate at high food concentrations was correlated with changes in pumping activity, which showed more frequent interruptions, or a lower level of water transport. Dreissena can filter out particles of diameter greater than 0.7 μm from the water. Retention reaches a plateau at about 5 μm particle diameter. Scanning electron micrographs of the arrangement of the cilia on the gill filaments are given.