Verification of Fluorescence Temperature Curves as Standards for Identification of Harmful Microalgae of Alexandrium, Heterosigma, Prorocentrum, and Pseudo-nitzschia Genera

Harmful algal blooms pose a serious threat to the ecology of coastal waters. Their timely detection is a crucial task in environmental monitoring. Optical spectrofluorimetry can be a promising approach in this field. The subject of this scientific work is the study of normalized fluorescence temperature curves (NFTC) as reference features of hazardous microalgae and confirmation of the possibility of identifying the genera of hazardous microalgae under study with their help. NFTC were obtained in laboratory experiments with microalgae monocultures under controlled conditions with registration of fluorescence spectra during linear heating (20–80°C). Verification was carried out by means of cluster analysis using the principal component analysis (PCA). The study has shown that NFTC demonstrate stable genus-specific patterns, making it possible to distinguish microalgae at the genus level with an accuracy of 90.91%. The use of PCA (three principal components which explain 94.22% of the variance) eliminates clustering errors caused by multicollinearity of the original features. The highest classification accuracy is achieved for Heterosigma akashiwa (100%), and the lowest, for Pseudo-nitzschia (86.15%) due to intrageneric similarity of NFTC. The study shows the need to expand the catalog of standards to enhance the statistical significance of the results.