Pelagic patterns along the Nemunas River-Curonian Lagoon transition, south-eastern Baltic Sea

The aim of this study was to reveal the patterns of structural and quantitative alterations of the plankton communities along the Nemunas River-Curonian Lagoon transition of the south-eastern Baltic Sea. Authors hypothesised the influence of the different phases of the seasonal plankton development (Bacillariophyceae vs. Cyanobacteria dominance) on the response of plankton communities due to hydrodynamic forcing. In order to assess spatial patterns of physical forcing, we used sediment grain size distribution data as a proxy for hydrodynamic regime. Zooplankton and phytoplankton communities in the Nemunas River were sampled to obtain a point of reference for their structure and seasonal dynamics. The changes in sediment grain size distributions, quantitative and structural alterations in zooplankton communities, as well as structural trends in phytoplankton communities were detected in the Nemunas River-Curonian Lagoon transition area. However, the expected abundance trend was not observed in the phytoplankton community, even during the Cyanobacteria-dominated period. Despite the observed gradient of the sediment structure along the river-lagoon transition, the expected value of the sediment characteristics for the pelagic conditions was not statistically proved.