Composition and seasonal changes in filamentous algae in floating mats

The occurrence of algal-cyanobacterial metaphyton mats in field (Konojad village) and artificial ponds (Poznań city) was investigated in the Wielkopolska region. The surface area of algal mats ranged between ca. 45% (natural pond) and 10% (artificial pond) of the total water surface, and the mats occurred from the water surface to the bottom; the algal diversity was similar in both types of ponds, i.e. about 10 taxa. The most frequently recorded and dominant taxa in small water bodies were: Spirogyra spp., Cladophora fracta in the artificial pond and Oedogonium spp., Cladophora rivularis in the natural pond. The dynamics of macroalgae demonstrated a pattern comprising different phases of taxa dominance. For example, April regarded as the first phase was characterized by a small amount of metaphyton, represented by Tribonema and Ulothrix taxa. In May, these species disappeared and were replaced by: Oedogonium spp. and Cladophora spp. which formed large aggregations in the field pond, and Spirogyra spp. which abundantly proliferated in the artificial pond. From June, however, Oedogonium and/or Cladophora significantly dominated in the mat structure and at the same time covered a large area of the water surface. The algal community was dominated by common algal taxa, among which single filaments of other taxa could also occur.