Taxonomic and functional classifications of phytoplankton in tropical reservoirs with different trophic states

Ecological approaches, such as functional groups (sensu Reynolds, FG) and exclusively morphological-based groups (sensu Kruk, MBFG), have provided a reliable tool for understanding phytoplankton responses to environmental conditions. Our study evaluated the concordance and the response of these two-functional classifications of the phytoplankton community to environmental variables in reservoirs of different trophic states (ultra-oligotrophic to meso-eutrophic). We also investigated the spatial and temporal concordance of the functional classifications with the taxonomic-based classification (species). Integrated water samples were collected in the euphotic zone in two climatic periods (summer and winter) to determine physical and chemical variables and phytoplankton. Higher water temperature and thermal stratification were observed in the summer, whereas higher free CO2 concentrations and mixing regime of water column in the winter. The 35 descriptors species showed a greater relationship to the trophic conditions of the reservoirs. The functional classifications revealed that the 17 FGs and 7 MBFGs were influenced primarily by seasonal variation of limnological conditions (water temperature, CO2 concentration, Zmix depth) and secondarily by trophic state of the reservoirs. Stronger similarity (higher than 0.70) was verified between species and FGs matrices (Mantel test, mainly) than between species and MBFGs ones. Procrustes and Mantel tests also evidenced high concordance between FGs and MBFGs matrices, exhibiting similar spatial and temporal distribution to environmental conditions. Thus, these ecological classifications demonstrated to be complementary tools, besides their particular degrees of detailing, to elucidate the functional responses of numerous phytoplankton species in studied tropical reservoirs.