Phytoplankton pigments in the Baltic Sea – mathematical description of chlorophylls and carotenoids content in different seasons and regions

This study aimed to trace the spatial and seasonal changes in pigment composition and to develop mathematical formulas to quantitatively describe their composition in different seasons in two regions: the open Baltic Sea region and the Gulf of Gdańsk. The analyses were carried out based on a 20-year database of empirical data from 1999 to 2018 obtained using the HPLC method. The proportion of chlorophyll a in the total content of pigments was stable irrespective of the season and region (62% ± 5%). In summer and autumn, a higher total amount of photoprotective carotenoids (about 15–17% in total pigment content) than photosynthetic ones was recorded. The concentrations of marker pigments are related to periodic increases in the corresponding algal classes. The spring bloom dominated by diatoms and dinoflagellates causes 40% content of fucoxanthin and 70% of peridinin in relation to their total content in all seasons. The highest percentage of chlorophyll b (up to 10% in open waters) and other pigments specific to green algae (neoxanthin, violaxanthin, lutein) were observed during summer and autumn. The 30% percentage of fucoxanthin confirms the occurrence of diatoms in autumn. The concentrations of groups and individual pigments have been determined as a function of chlorophyll a concentration. The best approximation results were obtained for the seasonal dependence of marker pigments for specific classes of algae. In summer and autumn – for chlorophyll b concentrations – zeaxanthin, fucoxanthin, alloxanthin and peridinin standard error factor ranges between 1.56 and 1.84.