Effect of food availability on the response of planktonic rotifers to a toxic strain of the cyanobacterium Anabaena flos-aquae

The ability of food concentration to modify the response of zooplankton to toxic cyanobacteria was examined using chronic (lifetime) toxicity tests with two rotifers, Brachionus calyciflorus and Synchaeta pectinata, and a strain of Anabaena flos-aquae producing the alkaloid neurotoxin, anatoxin-a. in a clone of S. pectinata, the cyanobacterium decreased both life span and lifetime fecundity to a much greater extent when the availability of food (Cryptomonas erosa) was low. Fecundity Nas the most sensitive parameter. In one experiment, the cyanobacterium (2.5 mu g ml(-1)) decreased fecundity by 29% at the highest food concentration (2 x 10(4) cells ml(-1)) but by 90% at the lowest one (3 x 10(3) cells ml(-1)). In two clones of B. calyciflorus, A. flos-aquae decreased lifespan, fecundity, and population growth rate, but there was only a tendency in one of the clones for the inhibition to be greater at lower food concentrations The degree to which toxic cyanobacteria affect the population dynamics of susceptible zooplankton taxa in natural communities may be greatly influenced by modifying environmental factors such as food availability and temperature, especially if these factors act additively or synergistically.