OCCURRENCE OF INTENSIVE BLOOMS OF CYANOBACTERIA Microcystis aeruginosa IN A TROPICAL ESTUARY

Abstract

Samples were collected in a longitudinal profile from the Jaboatao River estuary, covering the marine area (estuarine plume) through four stations in the estuary and four in the plume during the dry and rainy seasons, with the objective of evaluating the occurrence and the distribution of Microcystis aeruginosa cyanobacterial blooms. In both regions, it is possible to observe the influence of M. aeruginosa on the local diversity, which was considered to range from very low to low where this species was dominant. M. aeruginosa represented on average 95% of the total cyanobacteria in the estuary, while in the plume, this percentage reached 65%. The species M. aeruginosa was responsible for the predominance of cyanobacteria, both in the estuary and in the plume. The N/P ratios in the estuary and the plume were <16:1, indicating N as a limiting factor. A key issue in eutrophication science is the potential for N-fixing cyanobacteria to compensate for any deficiency in biologically available N, principally during the dry period. The high-temperature, nutrient-rich and polluted waters with little oxygen contributed to the abundance and bloom formation of M. aeruginosa . The AOU positive values (average: +2.7 and +2.1 ml/L, for the wet and dry periods, respectively) indicate high respiration rates. Keywords: Cyanobacteria, Algal Blooms, Nutrients, Tropical Estuary, Brazil.