Spatial distribution of phytoplankton in the subarctic estuary (Kem’ river, the White Sea)

The species composition and biomass of the phytoplankton (Ph) as well as hydrological characteristics were estimated in 4 spatial surveys in the subarctic tidal estuary of the Kem’ River and adjacent area of Onega Bay (White Sea, Russia) in June–July 2008–2011. The study area was divided into 3 zones (the river zone, the gradient zone and the marine zone), based on the salinity variation of the surface layer. In total, 318 species of Ph were registered, 143 species are found in the river zone, 225 — in the gradient zone, 106 — in the marine zone. The greatest number of species in all zones was represented by diatoms. The highest biodiversity of Ph in the surface layer was detected in the gradient zone. The averages of total biomass of the Ph in the surface layer (Bo) at different years varied in range 2.8–16.9 mg C/m3. Although Bo did not differ significantly between zones, with the exception of 2011, when Bo was the highest in the river zone, dissimilarity in the structure of the Ph in the river, gradient and marine zones were 61–95%. The similarity of the Ph at the stations of each zone was poor (22–53%) with the lowest values in the gradient zone. It is postulated that the tidal cycles determine the spatial and temporal heterogeneity of the composition, structure and abundance of Ph in the Kem’ river estuary in summer.