SUSPENDED CLAY AND THE POPULATION-DYNAMICS OF PLANKTONIC ROTIFERS AND CLADOCERANS

High concentrations (50-100 mg/L) of coarse, suspended clay (<2-μm particle size) caused large reductions in the population growth rates (rm) of 4 cladoceran species (Bosmina longirostris, Ceriodaphnia dubia, Daphnia ambigua, D. pulex). Juveniles were more susceptible than adults to suspended clay. Low concentrations (10 mg/L) of coarse clay, and high concentrations of fine clay (<1 μm), did not decrease, and sometimes increased, cladoceran population growth rates. Both the inhibitory effects of high concentrations of coarse clay and the stimulatory effects of low concentrations of clay were greater at limiting food (Cryptomonas) concentrations. The population growth rates of 4 rotifer species (Brachionus calyciflorus, Keratella cochlearis, Polyarthra vulgaris, Synchaeta pectinata) were not affected by high concentrations of coarse or fine clay, even at very low food levels. The population growth rate of the rotifer K. crassa was decreased by coarse clay. -from Authors