Spatial Distribution of the Diatoms Dactyliosolen fragilissimus and Cerataulina pelagica in the Autumn Phytoplankton of the Southeastern Baltics in 2020–2021

The mass development of diatoms Dactyliosolen fragilissimus and Cerataulina pelagica, atypical algae for the southeastern Baltic Sea (SEB) water area, were registered along the Sambia peninsula coastline in the middle of October 2020. Both species were found in the coastal zone off the western and northern coast of the Sambia peninsula from the Baltic Strait to port Pionerskiy at depths reaching 32 m. In early November 2021, C. pelagica bloomed both in the shallow coastal zone of the northern coast of the Sambia peninsula and in the deepwater zone of the SEB. The biomass of this species reached 2.8 g/m³. Both diatom species were abundant within the entire Russian exclusive economic zone (EEZ). The prevailing hydrological situation during the study period probably facilitated the penetration of the species into the study area by surface transport from the Arkona Basin.