Zooplankton community dynamics in the Bay of Boka Kotorska

The study on zooplankton included the analysis of qualitative and quantitative composition, as well as the analysis of spatial and temporal distribution of certain zooplankton groups and species in the Bay of Boka Kotorska. The research was realised at 3 locations within the Bay of Kotor, 2 locations within the Bay of Tivat, and 1 location within the Bay of Herceg Novi. Samples were collected using a plankton net with 125μm mesh size, with one vertical haul from the sea bottom to the water surface. Sampling was done either weekly, every 15 days, or once a month, with the aim to explain the high turnover rate of the abundance and distribution of zooplankton in shallow areas. During the 16-month research on zooplankton in the Bay of Boka Kotorska, we determined 81 taxa from 7 phyla. In the Bay of Kotor, we found 69 taxa, in the Bay of Tivat 70 taxa, and in the Bay of Herceg Novi 72 taxa. The annual density dynamics in all the three areas (within the three sub-bays, of Kotor, Tivat, and Herceg Novi) showed an increase in the warmer period of the year. The cause of high density values during the summer months in the Bay of Kotor was the appearance of the protozoan Noctiluca scintillans with a high population density, as well as the development of cladocerans. The development of cladocerans was the reason for the summer maximum in the Bay of Tivat and Herceg Novi as well, while the winter maximum in the Bay of Herceg Novi was the consequence of the high population density of copepods. The dominant group of zooplankton were copepods, with average percentages of 67% in the Bay of Kotor, 73% in the Bay of Tivat, and 81% in the Bay of Herceg Novi. Oncaeidae and Oithona nana were the dominant copepod taxa at all locations during the research. Maximum density of copepods was preceded by high densities of phytoplankton. The occurrence of a high population density of the ctenophore Bolinopsis vitrea in the Bay of Kotor is the first such occurrence recorded in the South Adriatic Sea, as well as the first mass occurrence of this species in the Mediterranean Sea. A high negative correlation between B. vitrea and copepods confirms the fact that ctenophores IX are very important predators, the activity of which might have a significant impact on the zooplankton communities. The results of this research indicate that it is necessary to use a plankton net with 125μm mesh size in order to obtain more precise values of the total zooplankton, because early stadiums of small cala