Planktic Cyanobacteria in the Lower Uruguay River, South America.

Abstract

Abstract:The Uruguay River is the second most important river in the Río de la Plata Basin. Taxonomical composition, abundance and distribution of cyanobacteria collected at nine sampling stations in the Lower Uruguay River (Uruguay) were analyzed seasonally from 2006 to 2009. A total of 24 taxa were identified, including 13 Chroococcales, 4 Oscillatoriales and 7 Nostocales species. The genera Dolichospermum and Microcystis presented the highest number of species among the planktic water bloom-forming cyanobacteria. The highest densities of cyanobacteria were recorded in summer during a bloom, with 6.2×10 6 cells.ml -1 , and the most abundant species were Microcystis aeruginosa and Dolichospermum cf. pseudocompactum. In this case, the toxicity analyses by HPLC did not indicate the presence of microcystin-LR. Phytoplankton growth in the Uruguay River was found not to be nutrient-limited. The high correlation of cyanobacteria densities with nitrogen and phosphorous compounds is directly related to changes in flow. Cyanobacteria densities increased with summer high temperatures in low flow conditions. The ANOSIM analysis showed no significant differences between zones and sampling sites, but there were temporal significant differences in relation to seasonal samplings. Radiocystis fernandoi KoMáreK et KoMarKová-Legnerová was recorded for the first time in Uruguay and Dolichospermum cf. pseudocompactum (Watanabe) WacKLin et al. was recorded for the first time in South America.

Dolichospermum uruguayense sp. nov., a planktic nostocacean cyanobacterium from the Lower Uruguay River, South America

“…High abundances of a compactly coiled morphospecies, preliminarily reported as D. cf. pseudocompactum (Ferrari et al 2011), have been repeatedly observed in the river since 2006 (Table 1). It commonly occurs mainly along a lower part of the river during spring and summer time (Ferrari et al 2011).…”

“…pseudocompactum (Ferrari et al 2011), have been repeatedly observed in the river since 2006 (Table 1). It commonly occurs mainly along a lower part of the river during spring and summer time (Ferrari et al 2011). The identical morphospecies was reported under a name Anabaena cf.…”

“…A transect line was established across the width of the river at each of the three sites, and divided into littoral, center and channel zones in each case. Seasonal samplings were carried out from July 2006 to November 2014 according to a biological monitoring program (BoCCardi et al 2010;Ferrari et al 2011). Two extra samplings were performed in summer 2009 and spring 2010, reflecting the occurrence dynamics of cyanobacterial blooms.…”

“…Morphometric parameters of the original population of the studied Dolichospermum sp., morphology of the isolated strain under culture conditions, and a comparison with morphology of the same Dolichospermum sp. observed by Ferrari et al (2011). The order of the data is as follows: (minimum) 25% quartile-mean-75% quartile (maximum).…”

“…One of the main factors affecting the water quality of the Lower Uruguay River is the construction of more than twenty hydropower dams. Other human activities, such as increasing urbanization and the expansion of agriculture, have recently favoured the proliferation of massive blooms of planktic cyanobacteria (Ferrari et al 2011).…”