Studies of phytoplankton in the Montenegrin coastal sea (Adriatic Sea), Montenegro (Yugoslavia), have been done in August and September 1998. Simultaneously, investigations were carried out in the area of Boka Kotorska Bay (Kotor and Tivat Bays) and outside the Bay, i.e. in the zone exposed to the influence of the open sea (Petrovac and Budva). It was found that the density of microphytoplankton is higher during summer, than in the autumn. So in the summer-period, as a consequence of stronger eutrophication process, mean-value of microphytoplankton density was 10**5 cells/cubic dm, and in autumn 4 x 10**4 cells/cubic dm. On the contrary, mean-value of nanophytoplankton density was higher in the autumn (5.2 x 10**6 cells/cubic dm) than in summer (3.5 x 10**5 cells/cubic dm), being a consequence of a decreasing eutrophication during colder period of the year. Having in mind the direct influence of the open sea outside the Bay, it is intelligible that population density of both phytoplankton size-fractions is lower along the Montenegrin coast, than in the Boka Kotorska Bay (Montenegro, Yugoslavia).

The present paper cites results of studying phytoplankton in the Grosnica Water Reservoir, Serbia (Yugoslavia). Seasonal investigations during 1997 and 1998 enabled us to establish composition and structure of the phytoplankton community, quality of the lake's water, and its trophic status. During the period of investigation, the phytoplankton community was characterized by forms of Cyanophyta, Pyrrophyta, Chrysophyta, Bacillariophyta, Euglenophyta and Chlorophyta. Qualitative analysis indicated that algae of the divisions Bacillariophyta and Chlorophyta are dominant in the phytoplankton, while saprobiological analysis using bioindicatory algal species showed that water of the Grosnica Water Reservoir during the given period was of the 1st and 2nd quality class.

In this paper, some data on long term seasonal investigation of hydrography and plankton are presented. The most important fact is that the whole area is exposed to the impact of the freshwater from numerous sources from the coast and submarine springs in Boka Kotorska Bay, as the impact of rivers Bojana and Drim. Exchange of the intermediate water-masses between Adriatic and Jonian basins is of great importance, too. So, basic ecological data, as well as characteristic phytoplankton and zooplankton groups and species are described.