Methods for Detection and Cell Abundance Estimation of Harmful Dinoflagellate Karenia Mikimotoi Using Peak Shifts of Chlorophyll Fluorescence Spectra

In our previous study, we found that the peaks of chlorophyll fluorescence spectra of K. mikimotoi and Chattonella spp. shift toward higher wavelengths, defined the degree of peak shifts as the fluorescence spectral shift index (FSI), and developed a method for detecting these harmful algal species and an in situ device, the harmful algal indication sensor (HAI sensor). In this study, we further established a method for estimating the cell abundance of harmful algal species based on FSI, and validated the method through laboratory experiments with cultured strains. Furthermore, a series of field observations for K. mikimotoi was conducted in Saiki Bay, Oita, in 2017 and 2018, and in Kujukushima waters, Nagasaki, in 2019 and 2021. Based on the results from observations, the detection method and the cell abundance estimation method were evaluated. High true positive fractions were confirmed in both methods. Significant positive correlations on a logarithmic scale were observed between the estimated cell densities and cell densities counted by microscopy.