Boosting the monitoring of phytoplankton in optically complex coastal waters by combining pigment-based chemotaxonomy and in situ radiometry

Research about the occurrence and extent of the cyanobacterial blooms in the Baltic Sea is critical due to their increased magnitude and frequency. Monitoring of the blooms is complicated due to their spatially and temporally heterogeneous nature. For adequate assessment of the water quality, phytoplankton dynamics needs to be tracked in large areas with high monitoring frequency. The main objectives of this study were (1) to describe phytoplankton community composition by pigment-based chemotaxonomy and validate the results with microscopy; (2) to improve the retrieval of information about phytoplankton community by combining remote sensing with laboratory based approaches (3) to develop a region-specific algorithm to calculate cyanobacterial blomass from reflectance spectra; (4) to detect and quantify potentially toxic bloom-forming cyanobacteria with molecular methods. In our study the reflectance-based chlorophyll a (Chl a) values overestimated the High-performance Liquid Chromatography (HPLC) values although the correlations with HPLC Chl a measurements were very strong (r(p) similar to 0.8, p < 0.001). We found that 709 nm/620 nm reflectance ratio correlated strongly (r(p) = 0.75, p < 0.01) to cyanobacteria wet biomass in CDOM-rich Vainameri even at low cyanobacterial biomass levels. Correlations between pigment-based chemotaxonomy and microscopy were significant in case of cyanobacteria (r(p) = 0.73, p < 0.01), cryptophytes (r(p) = 0.71, p < 0.05) and dinoflagellates (r(p) = 0.64, p < 0.05).