Dados da Tese de Doutorado
Author: Marcelo Manzi Marinho.
Title: Ecology of phytoplankton in the reservoir Juturnaíba, Araruama-RJ, Brazil: Structure and dynamics of the community, ecophysiological and methodological aspects.
Year: 2000. Full text (in Portuguese)
Abstract
The phytoplankton community dynamics of a water supply reservoir (Juturnaíba reservoir, RJ, Brazil - 22°33’S; 42°18’W) was analysed relating it with the variations of some physical and chemical factors, usually considered as the main regulators of phytoplankton biomass and composition. Laboratory experimental studies on the ecophysiology of main phytoplankton species, were performed for verification of some hypotheses postulated from field observations. Besides the ecological aspects, methodological aspects were also approached about the application of quantitative analysis of photosynthetic pigment technique for phytoplankton evaluation. The general pattern of phytoplankton biomass and composition variability assessed through the photosynthetic pigment analysis, were consistent with the results obtained by the classic method of organisms counting by the inverted microscope and confirmed the applicability of this technique for the study and monitoring of the phytoplankton. Analysis and comparison of the results under ecological theories, made easy a better understanding of the ecological processes driving phytoplankton structure and function. Our data supports the view that the delimitation of assemblages applies reasonably to the one found in tropical enriched systems, despite the original formulation for temperate regions. Another theoretical aspect also considered was the analysis of the empirical relationships between the resources and species abundance considering species ecophysiology. Both statistical descriptions and observations demonstrated the strong interactions among limitation conditions, in general, and the relative resource variability, in particular, in the regulation phytoplankton community structure. Concerning these considerations, nitrogen availability was considered one of the main regulating factors of seasonal succession observed in the Juturnaíba reservoir. Then, considering a competition scenery among the main registered species (Microcystis aeruginosa and Aulacoseira distans) it would be expected that the growth rates of these algae were influenced by N/P ratio. However, the results obtained in the experiments did not show significant differences among growth rates. Even so, M. aeruginosa presented superior capacity of production biomass, especially in low N/P ratios. Besides, the experiments demonstrated that M. aeruginosa has a larger potential than A. distans to influence the proportional availability of nutrients. Thus, N/P ratio variation in the Juturnaíba reservoir can have been consequence of cyanobacteria high capacities for nitrogen and phosphorus uptake, that suggests M. aeruginosa success and A. distans decline, seem to have been due to the largest capacity of the cyanobacteria in growing under smaller nitrogen availability. Our results pointed that it is important to do experimental studies linked with field observations, for a better understanding of the ecological processes in the phytoplankton community.
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