0023-6152

AA00697606

4363549

Improving technology for monitoring of harmful algal species is an important issue in fisheries industries, coastal management, and public health agencies. We have studied the possibility of monitoring harmful algal species using specificity of chlorophyll fluorescence spectrum obtained through the investigation of fluorescence properties of various species. We found that the peak wavelengths of the chlorophyll fluorescence spectra of Karenia mikimotoi and Chattonella marina var. antiqua slightly shift towards longer wavelengths compared to other species. Based on these findings, we have developed an in situ Harmful Algal Indication sensor (HAI sensor), which measures the Fluorescence spectral Shift Index (FSI), which is defined as the ratio of fluorescence intensities at two different wavelengths (670 and 690 nm) for representing the degree of fluorescence spectrum shifts, from the fluorescence intensities excited by blue light. The performance evaluation of HAI sensor for algal strains showed that FSI of Karenia mikimotoi and Chattonella marina var. antiqua were higher than those of other species. These results indicate that HAI sensor is able to detect these harmful algae. The field studies, conducted in Saiki Bay, Oita Japan in 2017, compared vertical profiles of FSI measured by HAI sensor with the species composition estimated by microscopic analysis. In these observations, HAI sensor successfully detected vertical distributions of Karenia mikimotoi. Furthermore, we have conducted long–term mooring observation using two units of HAI sensor, which were placed at mid and near-bottom layers and connected to a telemeter system in Saiki bay, Oita Japan in 2019. In this observation, HAI sensor detected the presence of Karenia mikimotoi at concentrations as low as 27 cells ml–1, suggesting that HAI sensor is useful for harmful algal blooms (HABs) monitoring and early warning systems.