ALGAL SIZE CLASSES AND PHYTOPLANKTON-ZOOPLANKTON INTERACTING EFFECTS

The dependences of the numbers of individuals in the chief groups of z ooplankton on the size classes of phytoplankton were analysed. Four cr iteria were used in sorting phytoplankton: length, width, sum of lengt h and width, and 'surface' (product of length and width). All dimensio ns measured were the maximum ones, i.e. including spines, mucilaginous sheaths, etc. Seasonal variability in the dimensions of algae was tak en into consideration. The highest correlation coefficients (r = 0.80) were obtained for rotifers using the surface criterion. Slightly lowe r values were found using length or the sum of the length and width. C ladocera and Copepoda significantly depended only on algae sorted acco rding to length and also, to a very small degree, on algae sorted acco rding to the sum of the length and width. Division of algae according to their surface seems to give more information than division accordin g to only one dimension. In the spring and summer, the environment was occupied by the smallest phytoplankton species; later it was dominate d by larger algae, and after that by still larger algae. Also consider ed is the use of apparent volume (as equivalent sphere volume to non-s pherical-shaped particles circumscribed over their largest dimensions) to construct size spectra. However, apparent surface as a rectangle i s less laborious to calculate, as is suggested here. Exemplifying coef ficients, K, of apparent magnification of the dimensions of the algal thallus, resulting from various ways of expressing these dimensions, w ere calculated.