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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 633

Carolyn W. Burns and John J. Gilbert; Effects of daphnid size and density on interference between Daphnia and Keratella cochlearis. Limnol.Oceanogr. 31(4):848-858, 1986

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The cladocerans Daphnia pulex, Daphnia ambigua, Daphnia rosea, Daphnia magna, and Daphnia galeata mendotae were tested in the laboratory for their competency to kill Keratella cochlearis (f. tecta) in the course of their normal filter-feeding behavior. At daphnid sizes >1.2 mm of body length, all five species killed the rotifers at rates that increased with body length as Y=0.485X-0.588 where Y is Keratella killed Daphnia-1 hr-1 and X is daphnid body length in mm. No species-specific differences in ability to kill rotifers were detected. Keratella was found in the gut contents of some Daphnia, indicating carnivory and a new pathway in trophic interactions in freshwater ecosystems. Keratella density did not affect Keratella mortality rate within the range tested (125-1,000/l). Daphnia cleared live Keratella from the medium at rates about three times those at which it cleared Cryptomonas from medium. Relations between Keratella mortality, Daphnia density, and Daphnia size were used to derive a family of curves from which the potential impact of Daphina-induced mortality on field populations of Keratella can be calculated. When the daphnids are large (>2 mm) and present at densities >1-5 individuals/l, they could have a major impact on the population dynamics of the rotifers.