Reproduction and planktonic phase of life of edible shellfishes, Mytilus galloprovincialis Lamk. and Ostrea edulis L. were the subject of the investigations. Biological and ecological characteristics of mentioned species have been studied in Boka Kotorska Bay (Adriatic Sea), Montenegro (Yugoslavia), having in mind data from the Adriatic Sea and Mediterranean. Beside, some localities from Boka Kotorska Bay, conveniet for their rearing, were described , too. A period of their appearance in plankton was considered before all.

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 main characteristics of catchment area of Boka Kotorska Bay (Adriatic sea, Montenegro, Yugoslavia), are high slope, carstic structure of ground, high precipitation (over 5000 mm a year) and high run-off of rain water. All rainwater is transported trough carstic ground structures quickly appearing in numerous sources along the sea cost or ones located on the bottom of the Bay. The large volume of freshwater which permanently empty into the Bay has the strong influence on the aquatic environment (salinity, temperature, transparency, etc.) and biota (abundance of the species) as it has been observed in the parts of Boka Kotorska Bay (i.e. Morinj and Risan Bays). The abundance and number of species are the good indicator of changes of aquatic environment and hydrological changes as well as of the capability of aquatic organisms to adapt quickly on the severe changes of conditions.

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.

Some new results of the monitoring and control of the sea-water quality along the Montenegrin coast of the Adriatic sea, Montenegro (Yugoslavia) are presented. The recent data from summer 1998 are compared with some previous results. So, increasing of temperature mean values and decreasing of salinity and sea-water density were found in comparison with the previous years in the whole investigated area. At the same time, the quality of the sea is growing worse, step by step. Faster changes were found in Boka Kotorska Bay, Montenegro (Yugoslavia) than outside of the bay, in the zone which is exposed to the stronger influence of the open sea. Finally, the most essential conclusion is that the solution of wastewater discharges becomes more and more important, especially in semienclosed Boka Kotorska Bay (Adriatic Sea, Montenegro, Yugoslavia).