6533b86ffe1ef96bd12cdb9e

RESEARCH PRODUCT

Ecotoxicological studies with the freshwater rotifer Brachionus calyciflorus. Resource competition between rotifers and daphnids under toxic stress

subject

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Abstract This study examined the ability of the freshwater rotifer Brachionus calyciflorus to coexist with the large cladoceran Daphnia magna, and the effect of sublethal concentrations of copper on the competition between both species. Preliminary laboratory experiments showed that large Daphnia (> 1.2 mm) can kill and rapidly exclude the rotifer B. calyciflorus in mixed-species cultures. Brachionus populations were suppressed by Daphnia both through exploitative competition for shared, limited food resources and through mechanical interference. At a food concentration of 1 X 105 cells/ml of Nannochloris oculata, competition caused high mortality rates and decreased fertility in the rotifer populations (1000 ind/1), even at low Daphnia densities (40 ind/1). Daphnia removed increasingly disproportionate shares of the daily algal food supply, leaving the rotifer populations to gradually starve to extinction. In other experiments the effect of sublethal copper concentrations (2.5, 5.0, 12.0 and 20 μg/1) on the competition between both species was analysed. Short experiments (5 days) were carried out to study the effect of this toxicant on the rotifer populations with and without Daphnia. Changes in the competitive relationships between both organisms under toxic stress and the possible ecological consequences of these observations will be discussed.