Some aspects of the seasonal distribution of flagellates in mountain lakes

In a larger regional survey in Tyrol, phytoplankton species composition and biovolume of mid-altitude and high-mountain lakes was studied. Results from eight lakes showed that flagellates (mainly Chrysophyceae, Dinophyceae, and Cryptophyceae) are important components of the phytoplankton.In the mid-altitude lakes a spring and an autumn maximum of Chrysophyceae as well as a summer maximum of large dinoflagellates are observed, whereas Cryptophyceae and Dinophyceae show irregular distributions. In the high-mountain lakes the seasonal variations of phytoplankton, including flagellates, are limited by the long duration of the winter situation. However similar sequences of phytoplankton assemblages as in the midaltitude lakes can be observed. Flagellates in high-mountain lakes are important to sustain phytoplankton standing crop under the winter snow and ice cover.In order to show similarities and differences of high-mountain and mid-altitude lakes, vertical profiles of phytoplankton from three lakes and seasonal patterns of Gymnodinium uberrimum from two lakes are compared. In addition the patterns of cryptomonads differing in their ecological requirements (Cryptomonas spp. and Rhodomonas minuta) are shown for a meromictic mid-altitude lake.