High food availability linked to dominance of small zooplankton in a subtropical floodplain

Abstract

Zooplankton body size is fundamentally affecting productivity, ecosystem respiration, nutrient cycling, and energy transfer and may be controlled by food availability but also water physical and chemical characteristics. However, the differences in control of water physical and chemical characteristics and food availability on zooplankton body size have rarely been investigated in subtropical systems. We tested the hypotheses that: (i) the type of environment, food availability, and water physical and chemical characteristics would influence body size distribution in the Upper Paraná River floodplain and nearby subsystems and (ii) in environments with higher food availability, small‐sized organisms would predominate showing higher abundance, whereas the opposite would occur in environments with lower food availability. To test these hypotheses, we performed partial redundancy and redundancy analyses (RDA). Our results showed that food availability, Secchi depth, and suspended inorganic matter influenced the body size structure of rotifers and cladocerans. Additionally, we observed that greater food availability was related to greater abundance of organisms, which were dominated by small‐sized zooplankton (size classes C2 and C1 in rotifers, and class C2′ in cladocerans). It was possible to associate different zooplankton body size spectra with phytoplankton biovolume and planktonic ciliate abundance. We suggest that large‐bodied cladocerans could have a competitive advantage over rotifers and small‐sized cladocerans when resources are scarce, because the large‐sized group could explore a wider range of resource types.