Composition of microphytoplankton of an estuarine Amazon River , Pará , Brazil

This work aims to describe the composition, relative abundance and frequency of occurrence of microphytoplankton in the Arienga River, determined from the analysis of ten samples collected in the rainy and dry seasons (May and September 2009 respectively), during five stations, using a plankton net with a mesh size of 20m. In the period studied, the rainfall showed an atypical behavior, compared to the average of the last ten years for the region, as pH and temperature did not undergone changes. A total of 128 species were identified, belonging to divisions: Dinophyta (0.78%), Chrysophyta (0.78%), Cyanobacterium (12.50%), Chlorophyta (26.56%), and Bacillariophyta (59.38%). Of Genres found, 17 had 100% of representativeness at in both fenods. It was possible to confirm two large groups, suggesting that the rainfall regime was the main controller factor of phytoplankton composition and spatial variation of species along the Arienga River. The phytoplankton diversity was considered characteristic of the Amazon region; therefore, it is considered that the human action did not affect the phytoplankton community of the Arienga River to date.


Introduction
2000; RIBEIRO et al., 2008;SOUZA;MELO, 2010).Estuaries are transition environments formed by the mixture It should be noted that since 1970, the municipality of of saltwater and freshwater, with different gradients of Barcarena has been receiving enterprises for the processing salinity and with fine sediments from seas and rivers, suffering of aluminum, available by Alunorte and Albras industries influence of tidal regimes (CAMERON; PRITCHARD, 1963; besides kaolin processed by the companies Ymeris Rio Capim KJERFVE, 1989b;MCLUSKY;ELLIOTT, 2004).
Caulim and Pará Pigmentos (BERREDO, 2001).Therefore, In these ecosystems, water is mainly related to the port activities are intense in the whole area, with heavy river maintenance of communities responsible for primary traffic of small and large vessels, mainly around the Miramar production, which serve as food for the remaining links in the terminal and SOTAVE Port (Guajará Bay) and Port of Vila do trophic chain (SCHIEWER, 1998;LOSADA et al., 2003;SILVA Conde (municipality of Barcarena), which are home to et al., 2005).Phytoplankton is within these communities and it deposits of petroleum derivatives with environmental risk of consists of a set of diverse taxonomic groups, which are able accidental oil spilling or leaks (ARRUDA, 2003).to adapt their metabolic functions to different environmental This study was conducted in the Arienga River, next to Pará and seasonal changes (GIANI; LEONARDO, 1988; CETTO, Pigmentos Company, with the aim of expanding the 2004).According to Reynolds (1997), the study of that information about the micro-phytoplankton community of the community, its composition, primary production and distribution Amazon region.have fundamental importance for the knowledge of the main functioning mechanisms of aquatic ecosystems.Thus, among 2. Material and Methods other factors, changes in this environment which are significant The municipality of Barcarena (Figure 1) -located at the in biological communities correlate negatively to the diversity mouth of the Pará River, in the metropolitan meso-region of of phytoplankton organisms and they occur associated with Belém (IBGE, 2007) -is bounded by the Marajó Bay and cut the increase of urbanization activities in watersheds by numerous rivers, water holes and creeks.It is characterized (MOREIRA-FILHO et al., 1974;PAIVA et al., 2006;COSTA et by specific natural conditions of little high topographic levels, al., 2010).In addition, it is observed that there is a gradual especially on the islands which are partly subjected to growth of phycologists studying phytoplankton composition in a descriptive manner in the Amazon region (MELO; HUSZAR, flooding (SOUZA; LISBOA, 2005).= p x 100/P, where p is the number of samples containing the species studied and P the total number of samples collected.According to Mateucci and Colma's criteria (1982) for determination of species, the characteristics of the phytoplanktonic community were classified in the following categories: very common (³ 80%), frequent (<80% and ³ 50%), uncommon (<50% and ³ 17%) and sporadic (<17%).

Statistical analysis
The analysis of variance (ANOVA) was performed in order to compare the physicochemical and biological parameters Sample design (spatial and temporal), followed by Tukey's test.Multivariate Collections were carried out in May (rainy) and analyses were carried out based on abundance matrices of September (dry) 2009 in five georeferenced sites (Table 1) the species and these values were transformed through the log along the Arienga River.The times and dates of the collections (x+1).For cluster analysis, we used Bray-Curtis's similarity were selected with the aid of tide tables for the Port of Vila index (1957), and dendrogram construction was based on do Conde (DHN, 2011).
WPGMA (Weighted Pair Group Method with Arithmetic Mean).Similarity Percentage analysis (SIMPER) was applied to indicate which species contributed substantially to the formation of groups defined by cluster analysis.All analyses were performed through the statistical program Plymouth Routines in Multivariate Ecological Research, version 6.1.6(PRIMER) and Statistics 7.

Sampling
Rainfall Rainfall data were obtained from the National Water Based on the average of the last 10 years (Figure 2), it Agency (2011) at Vila do Conde Station (Code: 148011), was possible to differentiate two characteristic seasonal located in the municipality of Barcarena, State of Pará.
periods: the first from January to June and the second from For the qualitative study of phytoplankton, we collected July to December, which correspond to periods of higher and the sample using a planktonic net (mesh size: 20 µm) and lower rainfall, respectively.In 2009, the total rainfall subsequently stored in polyethylene flasks containing (3,144.20 mm) was 1.7 times higher than the average of the Transeau solution.

Laboratory
The qualitative analysis of phytoplankton was performed by assembled cover slips and glass slides, which were observed in an optical microscope Olympus CX 40, preparing at least five slides for each sample.For diatom analysis, we used Müller Melchers & Ferrando's technique (1956) with a Zeiss scanning electron microscope, model LEO 1450 VP at Evandro Chagas Institute.
The calculation of occurrence frequency of the taxa found was expressed in percentage, taking into consideration the number of samples in which each taxon occurred and the total Physicochemical parameters number of samples tested, for which we applied the formula F The temperature on the surface of the water remained  °C.There were no significant differences between collecting the dry period (21 µS cm ).sites and seasonal periods.
The pH was acid with minimum value of 6.21 and Floristic composition maximum of 7.32 in May and October 2009, respectively; In the Arienga River, microphytoplankton was represented however, we did not observe significant differences between by 128 species distributed among the divisions Chrysophyta, collecting sites and seasonal periods.

Relative abundance
In the rainy season (May 2009), Polymyxus coronalis was classified as dominant (80% average of relative abundance) and Coscinodiscus sp. as little abundant (14% average of relative abundance) and the others were considered rare.In the dry season (September 2009), Polymyxus coronalis was abundant (45.4% average of relative abundance), Aulacoseira granulata was little abundant (average of 14.8%) and Coscinodiscus sp.(average of 14%) and the others were considered rare (Figure 6).

Discussion
In the period studied, rainfall had an atypical behavior, having been registered values 1.7 times higher than the average of the last 10 years for the northern region of Pará and 1.1 to 1.4 times higher than the estimated by Moraes et al. (2005) for northeastern Pará (2,300 to 2,800 mm).
Other physicochemical factors analyzed (pH and temperature) did not show large variations and these data are in accordance with findings by other authors in the Amazon region (PAIVA et al., 2006;RIBEIRO et al., 2008;COSTA et al., 2010).For this reason, authors who carry out researches relating physicochemical factors to the phytoplanktonic community (ESKINAZI-LEÇA et al., 1984;KOENING;MACEDO, 1999;AGAWIN;DUARTE, 2002) consider that these factors neither exercise control over growth and abundance of phytoplankton nor determine an annual pattern in tropical waters.
In the estuary, we observed differences in composition, frequency and relative abundance of species between the two seasonal periods studied.These differences are in accordance with studies carried out in estuaries and other coastal areas of Association of samples the State of Pará (SANTOS-FERNANDES et al., 1998; SHAH et The association of samples (Figure 7) allowed to al., 2008, 2009;COSTA et al., 2011).This seasonal variation highlight two groupings at 65% similarity level.Group I pattern can be found in other tropical coastal regions with small consisted only of dry season samples (September) and terrigenous influence, where the density of phytoplankton group II included samples of the rainy season (May).
increases during the rainy season, depending on the amount of Through Similarity Percentage analysis (SIMPER), it was nutrients washed down from the mainland (SANTOSpossible to identify the species that contributed most to the FERNANDES et al., 1998;ESKINAZI-LEÇA et al., 2004).The configuration of the two major groups formed in the microphytoplankton of the Arienga River was composed of association of samples (Table 3).Through variance analysis,   diatoms, chlorophyceae, cyanobacterias and dinoflagellates.predominate over the other groups throughout the year.Estuarine and coastal environments are often associated with Through Similarity Percentage analysis (SIMPER), it was regions with high stress, turbulence and under the influence of possible to confirm two large groups, suggesting that the coastal currents (TILSTONE et al., 2000;SMAYDA, 2002), similar rainfall regime was the main control factor of to water bodies found in this study and common to other phytoplanktonic composition.The similarity between the Amazonian ecosystems, such as the Guamá River (PAIVA et al., two collections carried out in 2009 confirmed spatial 2006) and Xingu River (COSTA et al., 2009).In addition, variation in species distribution along the Arienga River.Koening et al. (2003), Almeida et al. (2005)  ( COESEL, 1996).In addition, it was the second division with ANA -Agência Nacional de Águas.2011 (www.ana.gov.br).Acesso em the highest species richness.responsible for the variation of electrical conductivity.These Belém,Pará, data are in accordance to some authors' findings (AMOROS; BICUDO, C.E.M.; MENEZES, M. Gêneros de algas continentais do Brasil: BORNETTE, 2002;SILVA et al., 2009) v. 34, p. 497-517, 2007.The similarity between the two collections of biological  v. 27, p. 325-349, 1957.found that the seasonal variation can be influenced by . | Composition of microphytoplankton of an estuarine Amazon River, Pará, Brazil 2 Biota Amazônia

Figure 1 .
Figure 1.Area of study, with the collection points in the Arienga River, Amazon estuary.Fonte: Paulo Trindade.

Figure 3 .
Figure 3. Percentage distribution of microphytoplanktonic divisions identified in samples collected in 2009 in the Arienga River, Amazon estuary.

Figure 4 .
Figure 4. Frequency of microphytoplankton occurrence in samples collected in 2009 in the Arienga River, Amazon estuary.

Figure 5 .Figure 6 .
Figure 5. Number of species by collection site in the Arienga River, Amazon estuary, from May to August 2009.

Figure 7 .
Figure 7. Dendrogram of samples association collected in the Arienga River, Amazon estuary, from May to September 2009.

Table 1 .
Georeferenced collection sites along the Arienga River, Amazon estuary.
and Carmona et al.