Planktonic Cyanobacteria forming blooms in reservoirs of northeastern Brazil

This paper contributes to the inventory of cyanobacteria in freshwater environments in Northeastern Brazil. Forty-two samples were collected from 19 reservoirs between February 2009 and January 2010. Twenty-three species of cyanobacteria distributed among the orders Chroococcales (10), Oscillatoriales (8) and Nostocales (5) were identified, 12 of which constitute new records for the state of Pernambuco. The greatest degrees of species richness were recorded in three ecosystems (Alagoinha, Carpina and Ingazeira reservoirs). Microcystis was the most representative genus, with the greatest number of species (Microcystis novacekii (Komárek) Compère, Microcystis panniformis J. Komárek, J. Komárková-Legnerová, C.L. Sant’Anna, M.T.P. Azevedo & P.A.C, Senna, Microcystis protocystis W.B. Crow and Microcystis sp.). Cylindrospermopsis raciborskii (Woloszynska) Seenaya and Subba Raju (straight morphotype) had the greatest distribution (considered very frequent) and was present in 16 reservoirs (84.25%). Only four of the 42 samples did not have cyanobacteria.


Introduction
Cyanobacteria are cosmopolitan organisms considered to be the first photosynthesizers with chlorophyll a and primary producers to release oxygen into the atmosphere (Chorus & Bartram, 1999).These organisms exhibit broad ecological tolerance, which contributes to their competitive success.One of the striking characteristics of this group is the ability to grow in the most varied environments -from hot springs to cold oceans as well as in terrestrial environments (Domitrovic & Forastier, 2005).
However, freshwater ecosystems are the most suitable environments for the development of cyanobacteria, especially in tropical regions, which have the most favorable conditions for cyanobacterial blooms -a phenomenon characterized by the intensive growth of these microorganisms in water (Chorus & Bartram, 1999).As well as increases in nutrients, changes in temperature and mixing regime are important factors related to these blooms (Paerl & Huisman, 2008).
The extensive morphological plasticity and overlapping measures in species of cyanobacteria have caused problems in the correct identification of taxa, and therefore, according to Bittencourt-Oliveira et al. (2001), this can lead to a false understanding of the toxic potential of various species.Due to these problems, there are few works that aim as the primary focus aspects of taxonomic group, and thus, only about 5-10% of this diversity is known (Komárek, 2003).
In Pernambuco, studies on cyanobacteria began with Carvalho-De-La-Mora (1986) and were intensified after the "syndrome of Hemodialysis".Jochimsen et al. (1998) reported the occurrence of microcystin in the hemodialysis equipment of the Institute of kidney Diseases in Caruaru City (Pernambuco-Brazil) the place of contamination and death of humans by cyanotoxins.Then, Domingos et al. (1999) confirmed the production of microcystin by picoplankton cyanobacteria isolated from material collected in two reservoirs in the state of Pernambuco (Tabocas and Sr. José Maria), used to supply the city of Caruaru, suggesting that these organisms may have contributed to human poisoning in hemodialysis clinic of the municipality.
Then, several studies with distinct approaches (ecology, taxonomy, seasonal and spatial distribution) were carried out with cyanobacteria in many reservoirs used for public supply in the state of Pernambuco, (Bouvy et al., 2000(Bouvy et al., , 2001(Bouvy et al., , 2003;;Huszar et al., 2000;Aragão et al., 2007;Dantas et al., 2008Dantas et al., , 2011;;Lira et al., 2010;Moura et al., 2010Moura et al., , 2011;;Bittencourt-Oliveira et al., 2011).Considering the frequent blooms of cyanobacteria and the problems posed to aquatic ecosystems, the present study aimed to contribute to the knowledge of the diversity of these algae in reservoirs in Northeast of Brazil, since, in most cases, the blooms are formed by species potentially toxic, causing a risk to public health.

Study Area and Sampling
Forty-two samples were taken from 19 reservoirs located in different phytogeographic regions in the state of Pernambuco (Figure 1) (Table 1), which are characterized by high temperatures and dry periods, especially between October and March (summer); the winter (April to September) is featured by greater precipitation and milder temperatures.These ecosystems are used mainly for the public water supply and fishing activities of about three million inhabitants (ANA, 2012).
Sampling was carried out at a single point at the subsurface near the bank between February 2009 and January 2010.The taxonomic study was performed based on semi-permanent slides with samples of living matter analyzed immediately after collection and complemented with samples preserved in formalin and Transeau solution.Analyses were performed with the aid of a ZEISS optical microscope (Jenaval model) with a measurement ocular (magnification: 400X and 1000X).Morphological taxonomic characteristics of the organisms were analyzed, such as shape and dimensions of the heterocyst, akinetes, trichomes and cells as well as the presence of aerotopes and coloration.Identification was carried out to the smallest possible taxonomic level using the specialized literature (Komárek & Anagnostidis, 1986;2005;Anagnostidis & Komárek, 1988;Cronberg & Annadotter, 2006;Komárek & Zapomělová, 2007).
After analysis and taxonomic photomicrographs, samples preserved with formalin, were deposited in the Herbarium Professor Vasconcelos Sobrinho, Federal Rural University of Pernambuco (PEURF 50435 to 50476).
The total number of species identified was relatively smaller than that recorded in previous studies with emphasis at cyanobacteria community at Northeastern of Brazil (Aragão et al., 2007;Costa et al., 2009;Dantas et al., 2011;Lira et al., 2011) who recorded greater cyanobacterial richness.The lower number of taxa in the present study is likely due to the occurrence of blooms dominated by one or more species of cyanobacteria in the majority of reservoirs studied.The genus Microcystis was the most representative, with four species (M.novacekii (Komárek) Compère, M. panniformis J. Komárek, J. Komárková-Legnerová, C.L. Sant'Anna, M.T.P. Azevedo & P.A.C, Senna, M. protocystis W.B. Crow and Microcystis sp.).These same species were   and Aphanizomenon, respectively (Wacklin et al., 2009;Zapomĕlová et al., 2010).
The frequency, persistence and high density or biomass of one or multispecies of cyanobacteria in drinking reservoir are a greatest problem from the fact of some species, like: C. raciborskii, G. amphibium, Microcystis spp., P. agardhii and S. aphanizomenoides are potentially toxic (Figure 2a-b, d, f,  h-j).

Conclusions
Cyanobacteria were present in all the reservoirs studied, and among the 23 identified species, C. raciborskii was the only one considered very common, predominating in most environments.The genus Microcystis was the most representative, with four species (M.novacekii, M. panniformis, M. protocystis and Microcystis sp.).Ten new taxa were recorded for the first time for the state of Pernambuco.

Table 1 .
Location of the reservoirs, sampling dates, phytogeographical region and coordinates