The influence of biomass and structure of the crustacean plankton on the water transparency in the Saidenbach storage reservoir

Planktonic crustacean biomass as well as structure are important factors influencing water transparency. The significant dependence of the water quality (Secchi depth) on the concentration and the share of the Daphnia biovolume and not on the total Crustacea biovolume in the Saidenbach reservoir indicates that the density of the Crustacea is only a measure of the cleaning performance, if Daphnia dominates. Using the mean size, the influence of the crustacean structure on the Secchi depth can be recorded. If big size categories prevail (like Daphnia) the water transparency is high. The mainly occurrence of little species (Mesocyclops, Bosmina) results in lower Secchi depths. However, a well defined (significant) relationship is being prevented by the different feeding behaviour of the several species.