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Daphnia and Toxic Blooms of Microcystis aeruginosa in Bautzen Reservoir (GDR)
Author(s) -
Benndorf Jürgen,
Henning Manfred
Publication year - 1989
Publication title -
internationale revue der gesamten hydrobiologie und hydrographie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.524
H-Index - 52
eISSN - 1522-2632
pISSN - 0020-9309
DOI - 10.1002/iroh.19890740302
Subject(s) - microcystis , daphnia galeata , microcystis aeruginosa , daphnia , biomanipulation , biomass (ecology) , grazing pressure , zooplankton , phytoplankton , cyclops , biology , microcystin , cladocera , environmental science , zoology , ecology , grazing , cyanobacteria , nutrient , branchiopoda , bacteria , genetics
As a part of a whole‐lake, long‐term experiment in biomanipulation in. the hypertrophic Bautzen reservoir (G.D.R.), during three years (1984–1986) the dynamics of mouse‐related LD 50 of Microcystis aeruginosa was compared with the biomass development of this blue‐green and the grazing pressure exerted by Daphnia galeata. Since the three summer averages of the biomass of D. galeata revealed strong differences due to decreasing predation activity of fish from 1984 to 1986, the effects of different grazing pressure on Microcystis toxicity could be investigated under field conditions. Microcystis was nontoxic at the beginning of the growing season and developed high toxicity during its first strong biomass increase in summer in all three years. But this decrease of the LD 50 together with the first biomass increase of the season is found in quite different periods in different years (1984: August, 1985: July, 1986: June). It is obvious that the higher the mean effective filtration rate of D. galeata during summer is found the faster the toxicity of Microcystis is formed. If these observations are combined with findings of other authors, the conclusion can be drawn that the development of toxic Microcystis blooms seems to be promoted by a combination of five conditions: (1) Presence of a mixture of toxic and nontoxic Microcystis strains at the beginning of the growing season even if the portion of toxic strains is very low, (2) physical and chemical growth conditions which favour Microcystis over other phytoplankton, (3) high grazing pressure by zooplankton on edible food particles over a rather long period, (4) patchy distribution of the different Microcystis strains if nonselective filtrators such as Daphnia dominate the zooplankton, and (5) absence of defense mechanisms of Microcystis against grazing which are not coupled with toxicity (e.g. large colony size). These conclusions contribute to a better understanding of the possibilities and limits of in‐lake eutrophication control by biomanipulation and emphasize the need to combine top‐down and bottom‐up control mechanisms in eutrophic and hypertrophic waters.