EFFECTS OF INORGANIC SEDIMENT AND FOOD CONCENTRATIONS ON ENERGETIC PROCESSES OF THE ZEBRA MUSSEL, DREISSENA-POLYMORPHA - IMPLICATIONS FOR GROWTH IN TURBID RIVERS

We examined the effects of inorganic suspended sediment (0, 1, 10, and 100 mg.L-1) and food concentrations (0.1, 0.5, and 2.0 mg particulate organic matter (POM).L-1) on clearance, ingestion, respiration, feces , and pseudofeces production rates and assimilation efficiencies of ad ult zebra mussels (Dreissena polymorpha) under laboratory conditions a t 20 +/- 1 degrees C. Food quality indices (the proportion of inorgani c to organic material in feeding suspensions = IO ratios) ranged from 0.304 to 63.04. Suspended inorganic sediment above 1 mg.L-1 greatly re duced clearance rates, ingestion rates, and assimilation efficiencies of zebra mussels, and ingestion of POM was maintained only at high foo d concentrations. Pseudofeces were produced copiously by zebra mussels in the 100 mg.L-1 sediment treatment, and there appeared to be an inc reased metabolic cost associated with pseudofeces production. Declinin g food quality caused exponential declines in clearance, ingestion, an d absorption rates, water processing potential, and assimilation effic iencies, with the sharpest declines between IO ratios of 0.304 and 5.0 . IO ratios in turbid rivers often exceed 1.71, our experimental thres hold where scope for growth for zebra mussels was zero. We contend tha t zebra mussels in turbid rivers may exhibit low growth potential and may not stabilize at the high population densities seen in their lake counterparts.