Zooplankton Biomass in Ponds - Determination of Biovolume and Dry Weight

Abstract

The aim of this study was to evaluate the possibility of using simple screening methods to determine zooplankton biomass in ponds. Among the applicable methods, we selected sedimentation determination of wet biomass and dry biomass determination. Of the 369 samples analysed, the median volumetric zooplankton biomass was 0.012 ml.l-1 and the median dry weight of the samples was 0.44 mg.l-1. There was a relatively close relationship between the volumetric biomass determination and the zooplankton dry weight determination, allowing only one of these methods to be used. Due to the variation of results over a wide range of values, it is more appropriate to use a logarithmic expression for the correlation. No statistically conclusive relationship was found between the zooplankton biomass determined and any of the other physico-chemical or production parameters. Nevertheless, it was possible to trace the influence of fish production, altitude and nutrient content (nitrogen and phosphorus) on the size of zooplankton biomass. The use of screening determination methods can be recommended especially for long-term monitoring of sites to get a quick overview of zooplankton biomass in ponds. It is clear from the above data that predicting the development of the zooplankton community in ponds is highly problematic. Standard determination of zooplankton biomass at regular intervals during the growing season is usually not realistic outside scientific studies due to its technical and time-consuming nature. Therefore, for long-term monitoring of the zooplankton community at a given site, it is advisable to use relatively quick and inexpensive methods of determining zooplankton biomass, such as bulk biomass or dry weight. Although these methods do not give a detailed picture of the species structure of zooplankton, they do give information on the size of the total zooplankton biomass. Together with the determination of basic physico-chemical parameters and especially chlorophyll-a, a fairly good inference can then be made on the development of plankton communities.