COLONIZATION PROCESSES OF DIATOMS ON ARTIFICIAL SUBSTRATES IN THE RIVER DANUBE NEAR BUDAPEST (HUNGARY)

Periphyton was collected from sand-blasted slides exposed in the main channel of River Danube at Gild (1669 rkm). Samples were taken from 21 May to 23 November in 1984. Three to four days after placing the substrates into the river the first traces of an observable coating appeared. The formation of the algal coating in the Danube presented certain periodical features. From time to time, an essential decrease in the number of individuals could be observed, which generally coincided with changes in the structure of the community. This could be traced well, by grouping the algae according to morphological categories and following the temporal changes affecting these categories. The early phase of the colonization process is dominated by relatively large araphid and biraphid diatoms. In the second phase small bi- and monoraphid species are dominant. Finally, the medium size mono- and biraphid algae are dominating.