There are presented the results of investigations carried out in the Kotor Bay (Adriatic Sea), Montenegro (Serbia and Montenegro) during the winter months of 2004. The highest value of microphytoplankton as a greater size-fraction of phytoplankton is found in the surface layer during March (1.4 x 10**7 cells/cubic dm). The main edificator was diatomic species Skeletonema costatum with relative percentage about 100%. Obtained results point out that Kotor Bay belongs to the highest eutrophic or extreme eutrophic area. Similar result is found in the same period twenty years ago.

Eutrophicationn problems in the Kotor bay were studied monthly from September 2003 to August 2004. As a result of nutrient enrichment (directly dependent on human activities), phytoplankton growth was very intensive, reflected by high concentration of chlorophyll a (7.46 mg/cubic m).

In this paper, we used similarity index, such as Sorensen similarity index (S), Jaccard similarity index (Cj) and Percentage Similarity Index (PSC), to show similarities and contrasts within the qualitative structure of zooplankton of various bays within Boka Kotorska. This kind of statistical overview was made for Boka Kotorska Bay for the first time, so we believe that it is a valuable contribution to recent studies on zooplankton. Tables show the results for each index individually, as well as the smallest and greatest similarity among the bays. We also presented the number of recorded species in the Boka Kotorska Bay arranged by months for three different years.

The paper presents the seasonal overview of horizontal distribution and abundance for the species of genus Oithona in Bokokotorski Bay. Three species have been recorded. Oithona helgolandica and Oithona plumifera have a wide horizontal distribution within the Adriatic Sea, while Oithona nana is a typical euritherm and eurihaline form that occupies shallow and closed coastal areas along the eastern coast of Adriatic. Also presented are seasonal oscillations and quantitative presence of these species in the Copepoda population during 2002.

In the last few years, in Montenegro there were positive movements into fulfilling the principles of sustainable marine fishery, primarily throught introducing the Law on Marine Fishing and its rules. Institure of Marine Biology in Kotor, Montenegro, in cooperations with the Ministry for Agriculture, Forestry and Water Management of the Republic of Montenegro, works on undertaking of the measures that may ensure optimal regulation of fishing. These measures were based on scientific research, particularly on the estimates of parameters of population dynamics, biomass and maximum biologically sustainable utilization of economically important species on Montenegrin coast.

In this paper, there were discussed the results of ecological investigation of the Montenerin part of the Adriatic sea during the period 1996-2003. Evaluation of the sea-water quality was done in the coastal sea. The importance of multiannual ecological investigations was emphasized, too.