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JOURNAL OF PLANKTON RESEARCH | VOLUME 20 | NUMBER 8 | PAGES 1449-1462 | 1998
© Oxford University Press
research-article |
Can phaeopigments be used as markers for Daphnia grazing in Lake Constance?
Institute of Lake Research Untere Seestrafle 81,88213 Langenargen, Germany 1Department of Biology III (Ecology and Morphology of Animals), University of Ulm Albert-Einstein-Allee 11,89069 Ulm, Germany
Received on November 10, 1997; accepted on March 26, 1998 The formation of chlorophyll a degradation products was measured with natural phytoplankton from Lake Constance and Daphnia magna and native Daphnia as grazers in grazing experiments during spring bloom conditions using high-pressure liquid chromatography (HPLC). Chlorophyll a start concentrations were between 1.2 and 16.3 µg l–1; phaeopigment weights constituted 5% of chlorophyll a weight. Only phaeophorbide a was a marker for Daphnia grazing; concentrations of other phaeopigments (phaeophytin a, chlorophyllide a and two unidentified phaeopigments) did not increase during Daphnia grazing. Conversion efficiencies (chlorophyll a to phaeophorbide a) were between 0 and 43% on a weight basis, and between 0 and 65% on a molar basis. Conversion efficiencies were highest at high grazer density (40 Daphnia l–1) and after a 24 h exposure time. Grazing by microzooplankton probably led to the formation of the two unidentified phaeopigments. In Lake Constance, Daphnia density was significantly positively correlated with the phaeophorbide a/chlorophyll a ratio when it was <5000 Daphnia m–3. However, when higher Daphnia densities were included in calculations, then Daphnia density was positively, but insignificantly, correlated with the phaeophorbide a/chlorophyll a ratio. This suggests that when the level of food per Daphnia is low, then grazing is more efficient with less production of phaeophorbide a and a higher production of colourless products.
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