Spatial and temporal variability of zooplankton–phytoplankton interactions in a large subtropical shallow lake dominated by non-toxic cyanobacteria

Abstract

The size-specific and composition relationships between zooplankton and phytoplankton were evaluated in a large subtropical lake, as well as the influence of environmental variability on spatial scale considering temporal variation. Seasonal sampling was conducted for 2 years, covering three areas (south, centre and north) and the pelagic and littoral zones in Mangueira Lake (southern Brazil). The zooplankton to phytoplankton biomass ratio, usually, was very low, indicating a weak top-down control on phytoplankton; however, the strength of this interaction varied with zooplankton composition and temporal or spatial variability of the environmental factors. Environmental, bottom-up and probably top-down forces involved the structure of zooplankton, whereas phytoplankton was mainly controlled by nutrients. The phytoplankton predominant biomass consisted of colonial forms of non-toxic cyanobacteria. Rotifers (90–150µm) were more able to benefit from phytoplankton production, whereas large-bodied zooplankton, when present in higher biomass, were not related to phytoplankton. High contribution of small ciliates and significant positive correlations between zooplankton and total phosphorus presuppose that microbial food webs primarily sustain the macro-zooplankton production in this system. The environmental variability induced by wind action or diversification of niches also played a substantial role in the structure of the plankton community, and the strength of zooplankton–phytoplankton interactions.