Seasonal Responses of Filtration Rates to Temperature, Oxygen Availability, and Particle Concentration of the Freshwater Clam, Musculium partumeium (Say)

Seasonal filtration rates of a pond population of the freshwater pisidiid clam, Musculium par­tumeium (Say), were assessed by measuring the clearance of 2.02 µ.m latex beads from suspension and expressed in terms of FR = a(AFDW}b where FR = filtration rate (ml H20 · hr- 1 ) , AFDW = mg ash-free dry weight of a whole clam and a and b are constants. The a-values ( = FR of a 1-mg AFDW clam} vary seasonally with the highest rates corresponding to periods of maximum growth and reproduction in the spring and fall. Changes in b reflect the influence of body size on the weight-­specific rates (FR/AFDW). Seasonally a and b are inversely related. Therefore. seasonal increases in FR are proportionately greater for smaller clams. The 0,0 of FR is between 2-3 during the winter and decreases to 1.0 during the summer (temperature insensitivity) when clams are relatively inactive. At 20°c under aerobic conditions FR decreases as the concentration of suspension increases over a range of= 1.38-40 mg. · 1-1 with the FR for 1-mg AFDW clams going from 4.8 to 0.5; this minimum FR is maintained at higher concentrations. The amount of filtrate cleared (µ.g · clam- 1 • hr-1) initially increases as concentration increases (to = 13 mg -1 • I) then decreases before increasing again at concentrations\u3e =30 mg · I - 1• Ingestion must be less at higher concentrations since pseudofeces are produced at concentrations \u3e 22 mg · 1-1• Under anaerobic conditions FR is uniformly low at all concentrations. Seasonal responses of FR are assessed in terms of temperature. oxygen availability and particle concentration, and interpreted in terms of the interaction of growth, reproduction and population dyna­mics. These data have been integrated for 1-m2 of pond substrate. It is suggested that M. partumeium probably supplements filter-feeding with other mechanisms of energy intake such as deposit-feeding