AME 57:137-149 (2009)  -  DOI:

Changes in species composition during annual cyanobacterial dominance in a tropical reservoir: physical factors, nutrients and grazing effects

Maria Carolina S. Soares1,5,*, Maria Isabel de A. Rocha2, Marcelo M. Marinho3,  Sandra M. F. O. Azevedo2, Christina W. C. Branco4, Vera L. M. Huszar1

1Departamento de Botânica, Laboratório Ficologia, Museu Nacional, Universidade Federal do Rio de Janeiro, 20940-040 Rio de Janeiro, Brasil
2Laboratório de Ecofisiologia e Toxicologia de Cianobactérias, IBCCF°, Universidade Federal do Rio de Janeiro, CCS Bl.G, 21949-900 Rio de Janeiro, Brasil
3Departamento de Biologia Vegetal, Laboratório de Taxonomia e Ecologia de Algas, Universidade do Estado do Rio de Janeiro, R. São Francisco Xavier N 524, PHLC, 20550-900 Rio de Janeiro, Brasil
4Departamento de Ciências Naturais, Universidade Federal do Estado do Rio de Janeiro, Avenida Pasteur 458, 22290-240 Rio de Janeiro, Brasil
5Present address: Departamento de Biologia, Laboratório de Ecologia Aquática, Universidade Federal de Juiz de Fora, 36036-900 Juiz de Fora, Brasil

ABSTRACT: Trends in recent years have indicated that cyanobacterial blooms in tropical reservoirs are increasing in frequency, magnitude and geographical distribution. Funil Reservoir in southeastern Brazil has experienced eutrophication in the recent decades, resulting in lasting and intense toxic cyanobacterial blooms. As input of nutrients is high during the year, the aim of the present study was to evaluate the role of other variables related to changes in cyanobacterial biomass and composition. The dominant group found over the entire study period was Cyanobacteria (97% of total biomass), which contributed to low diversity. A shift of nitrogen-fixing (Anabaena circinalis and Cylindrospermopsis raciborskii) and non nitrogen-fixing (Microcystis aeruginosa) cyanobacteria was observed. Redundancy analysis indicated that physical factors such as temperature, changes in the mixing zone and light intensity were the main driving factors of the seasonal succession. Nitrogen-fixing cyanobacteria dominated in periods of low light in the deepest mixing zone, and also seemed to have experienced stronger grazing effects as the density of the large zooplankton group was related to cyanobacteria biomass. M. aeruginosa bloomed in warm stratified waters, high water levels and during months with more daylight, when the zooplankton density was drastically reduced. Although the long-standing dominance of cyanobacteria may be related to high nutrient availability, the present study showed that under high and constant input of nutrients, other factors, especially physical variables, present a more plausible explanation to promote changes in species composition.

KEY WORDS: Cyanobacterial bloom · Cylindrospermopsis · Microcystis · Anabaena · Zooplankton

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Cite this article as: Soares MCS, de A Rocha MI, Marinho MM, Azevedo SMFO, Branco CWC, Huszar VLM (2009) Changes in species composition during annual cyanobacterial dominance in a tropical reservoir: physical factors, nutrients and grazing effects. Aquat Microb Ecol 57:137-149.

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