The zooplankton community of Baltic Sea ports: diversity and seasonal dynamics

In this study, we investigated zooplankton composition and seasonal dynamics, as well as the influence of selected environmental factors on the zooplankton community in three ports on the Polish Baltic coast: Władysławowo, Gdynia and Gdańsk. Our aim was to determine whether harbours’ heavy traffic, chemical pollution and physical disturbances affect the zooplankton community, and whether new nonindigenous planktonic species occur in these habitats. Forty three zooplankton taxa were found in all three ports; however, it is important to note that no new nonindigenous species were observed in the port basins. The most influential environmental factors affecting the zooplankton community were: seawater temperature (17% of explained zooplankton variability) and transparency (4%), which were related to seasonal changes. Acartia spp. (although of different development stages) was the dominant taxon during the study, and the examined ports/seasons differed in the presence and proportions of less abundant taxa: the autumn and winter assemblages were dominated by Acartia spp. nauplii, the spring assemblage by numerous Polychaeta larvae, while Cirripedia nauplii and early development stages of Eurytemora affinis were particularly abundant in summer. In addition, changes in salinity (2% explained variability) had a particular impact on the zooplankton community and especially on the assemblage of Gdańsk Port, which was influenced by freshwater inflow from the Motława and Dead Vistula rivers. Our study has clearly shown that, despite severe physical and chemical disturbances in all studied ports, the composition and seasonal dynamics of the zooplankton community were similar to those of the Gulf of Gdańsk outside the ports.