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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13361

Effects of different plankton communities and spring bloom phases on seston C:N:P:Si:Chl a ratios in the Baltic Sea

Tobias Lipsewers*, Riina Klais, Maria Teresa Camarena-Gómez, Kristian Spilling

*Corresponding author:

ABSTRACT: Plankton communities and their temporal development have shifted towards earlier onset of the spring bloom and lower diatom-dinoflagellate-proportions in the Baltic Sea. We studied the effects of community composition and bloom phases on seston nutrient stoichiometry, revealing possible consequences of these shifts. Community composition, seston C:N:P:Si:Chl a ratios, physiological, and environmental variables were determined for four research cruises, covering all major sub-basins and bloom phases. A redundancy analysis (RDA) revealed that temperature and inorganic nutrients were the main drivers of community changes and e.g. high diatom-biomass was linked to low temperatures (growth phase). The effects of changing dominance patterns on seston stoichiometry were studied by applying a community ordination (NMDS/GAM). The C:N:P ratios increased from growth (103:14:1) to peak phase (144:18:1) and decreased after inorganic nitrogen was depleted (127:17:1). Taxonomic differences explained ~50% of changes in C:Si, N:Si, and Chl a:C, <30% for C:P and N:P, whereas C:N was unaffected. The fixed Chl a:C range (~0.005-0.04) was largely determined by diatoms, independent of the dominant species. Thus, C:Si and N:Si could be used to estimate the share of diatoms to the seston and Chl a:C to describe bloom phases and C-budgets during spring. Interestingly, mixed communities featured higher C:N:P ratios than diatom-dominated ones. However, as the community composition explained <30% of changes in C:N:P, we conclude that these ratios rather represent the total plankton physiology in natural plankton assemblages. We obtained valuable results on spring bloom dynamics and interesting projections to study e.g. species-specific nutrient ratios.