COMPARISON OF METHODS USED IN ZOOPLANKTON SAMPLING AND COUNTING IN THE JOINT RUSSIAN-FINNISH EVALUATION OF THE TROPHIC STATE OF LAKE-LADOGA

The results of a joint Russian-Finnish investigation on zooplankton in Lake Ladoga are presented, and a comparison is made between two sampl ing techniques, tube sampler and plankton net, and between two countin g methods. The precision of subsampling and sampling is further discus sed on the basis of zooplankton data gathered in Lake Saimaa, Finland. The comparison clearly indicates that a tube sampler is required for reliable sampling of small-sized animals, while a plankton net saves t ime and is a more economical sampler for large, rare or active animals . The comparison between the results obtained by Finnish and Russian w orkers, using different counting procedures, shows that the main group s of crustacean zooplankton are similarly counted and identified in th e two laboratories.