Low fish predation pressure in London reservoirs: II. Consequences to zooplankton community structure |
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Authors: | Jaromir Sedal Annie Duncan |
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Affiliation: | (1) Hydrobiological Institute CAS, Na sádkách 7, 37005 České Budějovice, Czech Republic;(2) Dept. Biology (Huntersdale), Royal Holloway, TW20 0EX Egham, Surrey, United Kingdom |
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Abstract: | The 1992 survey of zooplankton structure in fourteen London supply reservoirs showed the overall dominance of large-bodied zooplankton, mainly species of Daphnia. These reservoirs can be considered as ‘anti-fish’ by virtue of their steeply sloping concrete or brick sides. The average biomass of large Daphnia spp (retained on a 710 μm sieve) in the total zooplankton biomass was higher than 20% for twelve out of fourteen reservoirs. The cladoceran-copepod ratio was inversely correlated with both dominance of large-bodied Daphnia magna and cladoceran body-size structure. Parallelly, there were tendency of more efficient utilization of lowered algal crops in reservoirs dominated by large-bodied Daphnia spp. A graphical model is presented which relates daphnid species composition and zooplankton size structure to a presumed gradient of fish biomass in these reservoirs. |
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Keywords: | zooplankton structure Daphnia fish predation |
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