Environmental dissimilarity over time in a large subtropical shallow lake is differently represented by phytoplankton functional approaches

Abstract

The aim of the present study was to understand how different phytoplankton functional approaches responded to environmental variability in a large shallow lake, namely Lake Mangueira, in southern Brazil. This coastal lake has a maximum depth of 7m and is ~90km long and ~3–10km wide. Physical and chemical variables, maximum linear dimension, life forms, functional and morphofunctional groups of phytoplankton were analysed. The results showed that the phytoplankton were primarily comprised Cyanobacteria (63.9%), followed by middle-sized algae (21–50μm; 46.7%) and colonial non-flagellated taxa (63%). The highest percentage of total biomass was accounted for by the functional group ‘K’ (as classified by Reynolds et al. 2002; 36.3%), large mucilaginous colonies (46.79%) according to morphologically based functional classification and other large colonies (mostly non-vacuolated; 36.7%) according to morphofunctional classification. Dissimilarity analysis indicated a significant correlation between abiotic data and functional approaches (P=0.001). The dissimilarity in the functional compositions of phytoplankton was related to nutrient and light conditions, especially to silicon content and water transparency, in all functional approaches. The highest correlation with abiotic variables was seen for morphologically based functional group community structure, although the functional group composition of phytoplankton sensu Reynolds et al. seemed to be the most effective system in describing environmental variability in Lake Mangueira over the long term.