Effects of Particle Concentration and Season on the Filtration Rates of the Freshwater Clam, Sphaerium Striatinum Lamarck (Bivalvia: Pisidiidae)

The effects of particle concentration and season on the filtration rates of the freshwater clam Sphaerium striatinum Lamarck were assessed by measuring clearance rates of small (2.02 μm) latex beads from dilute suspensions. Filtration rates decreased as particle concentration increased over a range of 2-64 mg 1-1, with rates decreasing in similar proportion for clams of all sizes. For a 1-mg clam, rates decreased from approximately 8.4 to 0.57 ml clam -1 h-1. Seasonal filtration rates for adult clams peaked during periods of greatest reproduction. The patterns for smaller clams are similar, though proportional changes in filtration rates differ for various sizes of clams. It is estimated that clams occupying 1 m2 of stream substrate removed about 3.67 gCa-1. This is equivalent to 0.0004% of the carbon that flows past them annually. Filter-feeding provided only 24% of the calculated energy needs of the population, suggesting that another mode of feeding (e.g. deposit-feeding) may provide an important energy source for these forms