Classificação morfo-funcional do fitoplâncton e a relação com o micro/mesozooplâncton em reservatórios tropicais

Abstract

The classification based on morphology is an approach considered important to predict the effects of environmental changes on the phytoplankton community, being a useful tool to understand the herbivory and predation exerted by zooplankton. Environments that present different trophic states show changes in the phytoplankton-zooplankton interaction mode. The objective of this work is to analyze phytoplankton-zooplankton interaction, through phytoplankton functional groups based on morphology (FGBM), in two tropical reservoirs with different trophic states. Monthly collections were carried out from July/2016 to April/2017, in the limnetic region of the Tapacurá and Tabocas reservoirs, for biotic and abiotic analyzes. In situ experiments were also carried out in these ecosystems, where microcosms were maintained with micro and mesozooplankton addition and a control without zooplankton. Tabocas was mesotrophic during the study, the studied communities were predominantly constituted by small to medium chlorophytes and by mesozooplankton. Tapacurá, on the other hand, was supereutrophic during the study, constituted by filamentous and colonial cyanobacteria and by micro and mesozooplankton. In the experiments, it was verified that in the mesotrophic reservoir, in the presence of the micro and mesozooplankton, all phytoplankton morpho-functional groups presented growth rates with negative values. The ingestion rate, for this environment, showed that small to medium chlorophytes (2 - 50 μm) were highly ingested by micro and mesozooplankton. In the supereutrophic reservoir, the phytoplankton growth rate differed significantly only for unicellular flagellate and diatoms; however, only small flagellates with siliceous structures, medium-sized organisms without specialized structures and organisms with silica exoskeleton (diatoms) had a negative growth in presence of microzooplankton, and colonial cyanobacteria had negative growth in the presence of micro and mesozooplankton. In the rate of ingestion it was observed that the microzooplankton ingested in greater quantity colonial cyanobacteria, and the mesozooplankton, filamentous cyanobacteria. These results show that in mesotrophic reservoirs the phytoplankton community is constituted by phytoplankton groups highly susceptible to mesozooplankton ingestion, whereas in highly eutrophic reservoirs there is a predominance of cyanobacteria that are mainly ingested by microzooplankton.