Characterizing phytoplankton taxonomic and trait-based composition as a function of water quality, ecoregion, and fishing pressure at the landscape-scale

This study characterized the phytoplankton communities of 65 lakes across a large heterogeneous landscape classified by ecoregion in Ontario, Canada. Although phytoplankton communities were anticipated to vary according to ecoregion type based on their unique edaphic and water quality characteristics, there was no statistically significant difference (ANOVA, p>0.05) in taxonomic division, functional traits, size class, or size spectra across ecoregions. Taxonomic composition also did not vary across ecoregions, but redundancy analysis showed a separation of edible and inedible functional groups according to two ecoregion groupings. Additionally, cell-size spectra across the study lakes were significantly different across trophic status (oligotrophic, mesotrophic, and eutrophic) and recreational fishing pressure (high vs. low). Cyanophyta emerged as the dominant division across all lakes based on biomass, but also distinct from other algal groups with respect to environmental drivers. Total nitrogen and dissolved organic carbon were identified as significant positive explanatory variables of Cyanophyta biomass. The positive relationship with dissolved organic carbon may be related to Cyanophyta’s superior ability to grow in low-light conditions such as browning lake waters. Overall, our results indicate that ecosystem-scale factors such as trophic status and fishing pressure may play a role in phytoplankton community structure based on functional traits (i.e., edibility and metabolism) rather than taxonomic classification.