Assessing phytoplankton community composition using combined pigment and particle size distribution analysis

Abstract

Changes in phytoplankton composition reveal relevant information about the response of aquatic systems to environmental drivers. Here, we propose the combined use of particle size measurements and pigment signatures to analyze the changes in the composition of phytoplankton communities at a coastal location. Canonical correlation analysis (CCA) was applied to separate phytoplankton signals from non-algal components of particulate matter in concurrent measurements of particle size distribution and pigment concentrations (chlorophylls a, b and c). Using this method, we were able to identify phytoplankton community structure variations at size and functional levels associated with the water column during the spring to summer transition at a Mediterranean coastal site. Some taxa with characteristic size spectrum signatures such as Pseudonitzschia sp., which produced an intense (up to 5 × 10 cells l), but ephemeral bloom, could also be identified. The general patterns of phytoplankton succession obtained using this methodology were corroborated by light microscopy and flow cytometry identification. Phytoplankton biovolume comparisons between both methods were highly consistent (r = 0.75, p < 0.01). We consider that combined pigment and size structure analysis using CCA is a useful tool to determine reorganization patterns of phytoplankton via changes in species composition.