DIATOM, CHRYSOPHYTE AND PROTOZOAN DISTRIBUTIONS ALONG A LATITUDINAL TRANSECT IN FENNOSCANDIA

Diatoms, chrysophyte scales and cysts, and the siliceous plates of the coamoebae were studied from the surface sediments of 20 freshwater hab itats in Fennoscandia. The study sites are distributed along a latitud inal transect extending from southern Finland to northern Norway, span ning boreal forest through arctic tundra vegetational zones. Diatom as semblages were usually dominated by acidophilic, periphytic members of the genera Achnanthes, Fragilaria and Navicula. Marked shifts in diat om assemblage composition were recorded along the latitudinal transect , whereas scaled chrysophytes were rare in all study sites. Meanwhile, siliceous protozoa were common, but did not exhibit any noticeable tr ends in assemblage composition with changing latitude. A comparison of the Fennoscandian diatom assemblages with those recorded from freshwa ter sites near Yellowknife (central Northwest Territories, Canada) rev ealed similar trends in diatom assemblage composition with changing ec oclimatic zones in both regions. Moreover, canonical correspondence an alysis showed that diatom assemblages in cold, dilute tundra sites wer e effectively separated from sites with forested catchments from both the Fennoscandian and Canadian transects. The general similarity betwe en the two regions suggests that autecological data and the resulting environmental transfer functions based on diatom assemblages may event ually be joined from North American and European regions.