Spectral absorption and fluorescence characteristics of the Baltic Sea phytoplankton

The fundamental differences in spectral properties between algal groups are well established and can be used as a starting point in the identification of algal groups. Here, I will review the seasonal variability in spectral absorption and fluorescence characteristics of living phytoplankton in the northern Baltic Sea, and study their relation to phytoplankton community structure. Especially the phycoerythrin and phycocyanin fluorescence seem to be relevant indicators for picocyanobacteria and filamentous cyanobacteria, respectively.

Due to variable fluorescence and acclimation of pigmentation, deriving the biomass of spectral groups using the spectral fluorescence of multicomponent natural samples is not trivial and calls for advanced algorithms. For this purpose, multivariate methods (e.g. partial least squares, PLS) seem superior to univariate methods (e.g. classical least squares). PLS is especially applicable when signals from different constituents are overlapping, the background noise is high and variable, and not all of the optically active compounds are known. With experimental data, PLS -model was noted to give the best predictions for all spectral taxonomic groups - and with the accuracy needed for algal bloom detection. However, the success of PLS -model with other data-sets is not self-evident as these models are extremely sensitive to the calibration data-sets.

Possibilities for online detection of spectral phytoplankton groups by absorption and fluorescence methods will be critically examined.