Do charophytes influence biomass and species composition of phytoflagellates?

Abstract

Four Chara lakes, differing in their morphological features, physico-chemical water properties, catchment area characteristics and human pressure, were studied in order to recognize the influence of the charophyte PVI, proportion in the phytolittoral zone and species composition on phytoflagellate community. In one lake, the proportion of vegetation was lower than 50 % of the lake’s area while in the other lakes it was higher, in one of them reaching almost 70 %. Phytoflagellate diversity, biomass and relative biomass (proportion in total phytoplankton biomass) were studied monthly during the growing season. Both small and shallow as well as large and deep Chara lakes supported high proportion of phytoflagellates exceeding even 90 % of the total phytoplankton biomass, but our results suggest lake-specificity in the composition of phytoflagellates. Phytoflagellate species appeared among the phytoplankton dominants in each month and in each lake. Out of four phytoflagellate groups examined, the biomass of cryptophytes and relative biomass of haptophytes differed significantly in the Chara lakes studied. Cryptophytes were related to the human pressure on one hand and to the cover of charophyte vegetation on the other hand. The use and type of catchment area seem to be the main factors influencing the biomass and the structure of phytoflagellate assemblage.