Responses of Plankton to Filamentous and Toxic Blue-Green Algae

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This study examines three specific hypotheses regarding the responses of planktonic rotifers and cladocerans to potentially interfering non-toxic filaments, toxic cells, and toxins of blue-green algae. The hypotheses, supported by some field observations and laboratory experiments, predict that: 1) rotifers, especially those with specialized diets, will beless susceptible than cladocerqans to non-toxic filaments and toxic cells of blue-green algae; 2) the presence of such filaments and toxic cells will reduce the ability of cladocerans to competitively suppress rotifers; and 3) rotifers and cladocerans will be equally susceptible to exotoxins and extracted endotoxins of blue-green algae. The hypotheses will be tested by: 1) determining the effects of non-toxic filaments, toxic cells, and soluble toxins of blue-green algae on the intrinsic rates of natural increase, feeding rates, feeding behaviors, and swimming behaviors of a variety of rotifers and cladocerans; and 2) determining the abilities of rotifers to compete with cladocerans in long-term, mixed-species cultures with and without non-toxic filaments or toxic cells of blue-green algae. The results of these experiments will be useful in understanding and predicting the effects of these algae on zooplankton population dynamics and species structure in natural communities. Interfering blue-green algae, like zooplanktivorous fish, may slelectively inhibit cladocerans and there by favor the development of rotifers.