During the study we recorded narrow margins between zooplankton distribution and the ecological characteristics of water in Bokakotorska Bay (Adriatic sea, Montenegro). Various species show different vulnerability to environment quality. Some are defined as indicators, with low tolerance for the ecological variation of environment, and their distribution is limited to the particular type of water masses within the sea. The limiting factors are different for various species, and their indicator status is determined by their distribution. The indicator type, based on monitoring of particular species, may define a biotope, with the help of statistical analyses that identify the main time and spacial behavior patterns of a species, and my allow future ecosystem changes to be anticipated. In this paper we paid particular attention to the indicator species Oithona nana (Giesbrecht).

A great floristic variety has been noted according to qualitative analysis of phytoplankton. The presence of 187 taxa from 7 divisions of algae has been noted. The results of quantitative analysis show the dominance of centric diatoms. The high values of biomass that point out on the trophicity increase are noted on the strech from Nestin to Zemun (Serbia) with the maximum at Centa (Serbia) with 15,885 mg/cubic dm. Downstream Zemun, it has been noted gradual decrease of biomass up to Pancevo (Serbia), and afterwards downstream the considerable reduction all the way up to Brnjica (Serbia), where the value of algal biomass was 1,697 mg/cubic dm.

In this paper the results of zooplankton investigations (and its dominant group Copepoda) were presented from the part of the Boka Kotorska Bay with more intensive circulation with the open sea, from summer of 2005. Some results from the open South Adriatic were given, too - from the frontal zone exposed to anthropogenic eutrophication of Bojana and Drim rivers, and the impact of oligotrophic South Adriatic, simultaneously.