Identification and Analysis of Annual Cycles of Phytoplankton in the Kiel Fjord (Baltic Sea): Who is Playing and by Which Rules?

Abstract:

Coastal waters frequently experience a complex interaction of physical and chemical factors with the ecosystem. This can be demonstrated with water and phytoplankton samples collected at monthly intervals from the Kiel Fjord in the Baltic Sea in Northern Germany since 2016. From these samples, the population and biodiversity of phytoplankton at this location are examined with respect to seasonality and environmental influences. First, a baseline for various aspects had to be established, from which particular events can then be extracted for closer study: In the data, 30 different genera of phytoplankton were identified. While some are present in every sample (e.g. Ceratium), others only appear infrequently. Some genera are representative of the spring bloom (e.g. Skeletonema and Thalassiosira), while the concentrations of Ceratium and Chaetoceros have their maximum in autumn. In phases of very low nitrate concentrations measured in the water samples, cyanobacteria are found. Total cell counts of all species correlate well with chlorophyll concentrations. Based on the monthly data, the interannual average of species richness is highest in April (14 genera) and lowest in October (6 genera). Further studies will try to determine the effects of specific events on the phytoplankton population, such as a particularly cold winter or periods of increased freshwater input with associated low salinities.