No abstract

Abundance, biomass, and taxonomic composition of the ciliate community were studied in the surface waters along a transect between 50°S 61°W and 48°N 5°W (Atlantic

Confocal laser scanning microscopy in combination with digital image analysis was used to assess the impact of protozoa on bacterial colonisation of surfaces. Bacterial biofi lms were developed from activated sludge in microscope fl ow cells and were exposed to the grazing pressure of protozoa. The protozoan community from healthy activated sludge and a culture of fl agellate Bodo saltans were used as grazers. Experiments comprised 48-h incubations in 3 treatment variants: bacteria with protozoa, bacteria with protozoa added after some time and bacteria without protozoa. When necessary, the elimination of protozoa from the inoculum was carried out with cycloheximide and NiSO 4 . Experiments demonstrated that protozoa from healthy activated sludge initially disturbed the biofi lm development but later they could stimulate its growth. Similar results could be established in the experiment with Bodo saltans (inoculum: 1000 cells/ml), however differences were not statistically signifi cant. The fi nding that protozoa support biofi lm development during specifi c stages may be relevant for biofi lm studies with mixed environmental biofi lm communities.

Protozoan communities were studied in the coastal zone of the southern Baltic Sea. Stable environmental conditions and typical, bimodal seasonal changes in the protozoan biomass were observed at the sampling site in Sopot (2003Sopot ( -2004. At the sampling site in Ustka (2007)(2008), strong benthic resuspension and irregular impacts of fresh water resulted in atypical seasonal changes in the protozoan biomass with a summer peak only. The mean annual biomass had similar values at both sites: 43.2 µg C dm -3 in Sopot and 38.6 µg C dm -3 in Ustka. The protozoan community in Sopot was dominated by ciliates (48% of the biomass), whereas in Ustka − by heterotrophic nanoflagellates (53%).

Nutrient status, mainly the availability of nitrogen and phosphorus, is essential to understand the present state of a lake ecosystem and to predict its possible further development and proper management strategies within the drainage basin [1]. Because each lake ecosystem is influenced by lake morphometry, basin geology, and climate, nutrient sources and nutrient cycling in lake waters differ between lakes [2]. Numerous case studies are needed to formulate more general patterns of lake ecosystem functioning in relation to their specific characteristics. Lake Gardno belongs to a type of shallow lake located along the southern Baltic Sea coast and influenced by seawater intrusions. Such coastal lakes were grouped separately within the Polish abiotic typology prepared according to the requirements of the Water Framework Directive 2000/60/EC [3]. It represents the type of lake which can be considered a "shallow" lake. Shallow lakes differ in their hydraulic behavior and ecological functioning from deep lakes.