Controle Top-Down da comunidade fitoplanctônica em reservatórios eutróficos tropicais: um cenário de biomanipulação com a adição de cladóceros planctônicos

Abstract

The growing levels of eutrophization in the aquatic ecosystems have brought attention to studies that research the control of microalgae bloom, since some of these organisms can produce toxins capable of causing damage to a large variety of living beigns. Looking for possible solutions to this ecological imbalance, there is a growth in the levels of preoccupation concerning the particularities of the phytoplankton-zooplankton relation, especially due to the direct role of the zooplankton in the dynamic of aquatic ecosystems. Therefore, this study aims to analyze the potential of cladocerans in acting on the top-down control of the phytoplanktonic biomass of the eutrophic reservoirs. The study consists of two experiments: the first was realized under controlled laboratory conditions with the phytoplanktonic community of the Apipuco's weir, in Pernambuco, and the second was realized in situ with the phytoplankton from the Tapacurá's reservoir, also in Pernambuco. Through the laboratory experiment, a significant decrease of 67.39% and 40.17% from the total biomass in the dry and wet weather periods, respectively, was observed after eight hours in the higher zooplanktonic density. On the other hand, the cladocerans were not successful with the control of the phytoplanktonic biomass through the experiment. However, the treatment with the duplicated zooplanktonic biomass from the Tapacura's reservoir was capable of significantly reducing the biomass of almost every morphofunctional groups. Besides that, in both experiments the species that presented the most linear dimension, with values between 0 and 100 μm, did not present reductions in the size in both the seasonal periods, suggesting that the cladoceran consumed them whole, while only in the experiment I species larger than 100 μm were reduced, mainly through treatments with addition of 200 and 300 ind L-1. Thus, the natural zooplanktonic community from the Tapacura's reservoir and Macrothrix spinosa demonstrate to be potential controllers of the phytoplanktonic growth in aquatic eutrophic tropical ecosystems.