Diurnal Variation of Water Chemistry and Zooplankton in Little Mere, Cheshire, UK, in 1993 and 1994


Abstract: In Little Mere, diurnal sampling of the zooplankton at three different habitats in 1993 provided little evidence to support the data of Timms and Moss (10) that cladocerans move out from refugia at night to graze in open water. The floating-leaved water lily, appeared to be more efficient at providing refuge to D. hyalina in the presence of high planktivore fish predation than the submerged plant beds and the open water. This might be due to unfavourable physical and chemical environmental conditions associated with the water lily bed for fish feeding, a possibility supported by the findings of very low dissolved oxygen and pH values in the water lily beds. Potamogeton berchtoldii beds appeared to be more favourable habitats for submerged plant associated zooplankters than for open water grazers, probably due to the high predation pressure of planktivorous fish on the latter. The findings of this study suggest that it is important to have a better understanding of effectivness of submerged plants at provison of refuges for open water Cladocera against fish predation to combat eutrophication by using biomanipulation.

Keywords: Floating-leaved plants, submerged plants, Daphnia,plant-bed associated grazers, refuge.

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