A Method of in situ Measurement for Counting and Sizing of Blue-Green Alga Particles by the Detection of Fluorescent Components at Two Wavelengths

Abstract

To understand the ecosystem of lakes and the ocean, we have developed a new in situ measurement system for counting and sizing alga particles. The system is based on the fact that the laser induced fluorescence from the phytoplankton changes its spectrum according to the phycocyanin quantity which is abundant in blue-green algae. In the system, blue-green algae are discriminated by measuring the ratio of fluorescence components at the two wavelengths (655 nm and 685 nm) emitted from the phytoplankton irradiated with a 532 nm laser beam. The system gives particle size distribution for each alga in the mixed phytoplankton of blue-green and green algae.