USING ABSORBANCE AND FLUORESCENCE SPECTRA TO DISCRIMINATE MICROALGAL PHYLOGENTIC GROUPS AND TAXA

Abstract

Millie. D. F.1, Kirkpatrick, G. J.2, Schofield O. M. E.3, Johnsen, G.4, & Evens, T. J.1 1USDA‐ Agricultural Research Service, New Orleans, LA 70124 USA, 2Mote Marine Laboratory, Sarasota FL 34240 USA, 3Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08903 USA, 4Trondheim Biological Station, University of Trondheim, N‐7018 Trondheim, NorwayDeveloping optical detection techniques for discriminating phytoplankton species in mixed assemblages has long been a goal of aquatic scientists. Previously, the authors described methods to discriminate the optical absorbance spectra for a red‐tide dinoflagellate within both hypothetical mixed cultures and mixed natural assemblages. To this end, the utility of absorption and fluorescence‐emission spectra for further discriminating among algal phylogenetic groups (and potentially taxa) and for discriminating phycobilin and non‐phycobilin containing algae, respectively, was examined in laboratory cultures. A similarity index algorithm, in conjunction with fourth‐derivative transformation of absorbance spectra, provided discrimination among/between the chlorophyll [Chl] a/phycobilins, Chl a/Chl b, Chl a/Chl c/fucoxanthin, Chl a/Chl c/peridinin spectral classes as well as closely‐related phylogenetic groups within a class. Among the cyanobacteria, diatoms, and chlorophytes tested, absorbance spectra of taxa possessing dissimilar cell morphologies were discriminated with the greatest range of differentiation occurring among cyanobacteria. Interestingly, spectra for problematic cyanobacteria (including taste/odor metabolite‐ and toxin‐producing species) were discriminated from spectra from each other and from other cyanobacteria. Fluorescence‐emission spectra were distinct among algal spectral groups; similarity comparisons of fourth‐derivative plots discriminated the increasing contribution of distinct taxa containing different phycobilin pigments and between phycobilin and non‐phycobilin containing taxa within hypothetical mixed assemblages. The potential application for in situ instrumentation incorporating such approaches in monitoring programs, particularly those targeting harmful algal blooms, is elucidated.