Study of the zooplankton productive processes in a subtropical reservoir: an experimental demonstration in enclosures

Abstract

The present study will be carried out in Fazzari reservoir, a shallow and oligotrophic environment located in São Carlos District, São Paulo State, Brazil. The main objective is to use this ecosystem as a model for the evaluation of the influence of the sediment, air and light on the plankton productive potential in a small freshwater system. Experimental demonstration will be realized using enclosures. This study will focus on complexes ecological processes in order to verify the consequences of the interactions between several aquatic compartments and the planktonic community, as well as the influence of chemical and physical dynamics of the environment on this community. In the aquatic ecosystems, the organisms have reciprocity with the environment, so that alterations in the equilibrium between physical, chemical and biological variables could promote a great impact on the biota, with effects over the structure and function of such ecosystems. In this context, the planktonic community constitutes an important element in the functioning of lakes and reservoirs, once it is the base of trophic chains of natural aquatic ecosystems, constituting the major link with the higher trophic levels, like that represented by filtrators fishes. So, in order to achieve the proposed objectives, it will be carried out in situ experiments using enclosures, to evaluate the planktonic populational dynamics in different experimental situations (with and without the influence of sediment and the air), which will be compared to the natural environment. The effects of such treatments will be discussed in function of water's dynamic of nutrients, specially phosphorus and total nitrogen, and its impact over plankton biomass, productivity and trophic relationships. It will be determined the main water's physical and chemical characteristics, the populational structure of phytoplankton (composition, numerical density and chlorophyll a), zooplankton (specific composition, numerical density, biomass, secondary production, growth rates and populational dynamics) and biomass of bacterioplâncton and nanoflagellates. Life history data of the dominant zooplanktonic species will be obtained by rearing animals in laboratory, and will be used to estimate secondary productivity. Such life history information could subsidize the development of new technologies to the large scale cultivation of zooplankton to feed larvae and young fishes in intensive cultivation systems. The optimization of such cultivation process necessarily involves previous knowledge of reproductive cycles, fecundity, etc. It is also expected that the results of this study, concerning the sediment impact on zooplankton populations, will help the aquaculture in the idealization of cultivation pounds to the fishes' larval phases or planktivores species. (AU)