Does environmental heterogeneity explain temporal β diversity of small eukaryotic phytoplankton? Example from a tropical eutrophic coastal lagoon

The temporal beta diversity of small eukaryotic phytoplankton in a tropical urban coastal lagoon (Rodrigo de Freitas Lagoon, Brazil) was characterized throughout two annual cycles (2012-2103) with twice-weekly sampling. Small eukaryotic phytoplankton (< 20 mu m) were very abundant (above 1 x 10(3) and up to 6.2 x 10(5) cells mL(-1)). Small eukaryotes were also the most diverse phytoplankton group, showing high temporal variability at the species level that was represented by seven taxonomic divisions. Temporal beta diversity was positively related to environmental heterogeneity on a short-time scale. Although abundance peaks of the main species were positively related to NH4 inputs, selection of species ultimately depended on the simultaneous interaction among several physical-chemical variables acting hierarchically on different temporal scales (first seasonally and then on a short-time scale). Considering the numerical importance of small size fraction phytoplankton, information relevant to the management and conservation of coastal lagoons could be incomplete if the floristic composition and temporal species turnover of pico- and nanophytoplankton species are not properly determined.