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Changes of the plankton community in a shallow, subtropical lagoonal system and its relation to environmental conditions were investigated during an annual cycle to provide information on its spatial and seasonal variation pattern.

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The study carried out at four sites three in the Peixe lagoon and one in the Ruivo lagoonwhich are located Algas diatomeas yahoo dating the Lagoa do Peixe National Park, southern Brazil. The system has a temporary connection to the Atlantic Ocean by a narrow channel. The phytoplankton density was higher in the Peixe lagoon whereas the specific richness was higher in the Ruivo lagoon which is also a site with the lower salinity. The phytoplankton biomass near the channel showed seasonal variation with the highest value in fall and lowest in winter.

Zooplankton richness was inversely correlated with salinity, and had the highest values in the Ruivo lagoon. Algas diatomeas yahoo dating analysis indicated seasonal and spatial patterns in plankton community in this lagoonal system, related to variation in salinity. In addition, the wind action and precipitation were important factors on the spatial and seasonal salinity changes in the lagoon with direct influence on the plankton community dynamics.

Spatial and seasonal heterogeneity of phytoplankton are regular features in coastal lagoons in different parts of the world, and has been the focus of studies in temperate Armi et al. Algas diatomeas yahoo dating systems fluctuate between freshwater and hypersaline conditions Kjerfverelated to the inflow of seawater or fresh water, as well as to wind action salt spray.

Moreover, wind velocity and direction may influence the magnitude of sediment resuspension and water exchange, modifying water chemistry and physical characteristics Muller et al. Although coastal lagoons Algas diatomeas yahoo dating important environments, both "Algas diatomeas yahoo dating" and economically, only a relatively small number of studies have been carried out in subtropical and in permanently enclosed coastal lagoons Hennemann and Petrucio Phytoplankton community structure of subtropical lagoons is related to the spatial salinity gradient Callegaro et al.

In addition, the spatial heterogeneity of subtropical shallow lake plankton is strongly influenced by hydrodynamics, while seasonality impacts community composition Cardoso and Motta Marques a, b, Crossetti et al.

In some tropical lagoons, spatial variation in species composition occurred due to changes in salinity and nutrients, caused by the opening and closing of channels Melo and SuzukiMelo et al.

The composition of phytoplankton in temperate zones has been driven more strongly by seasonality than by spatial changes in salinity Ramdani et al. In the southern Mediterranean, community structure was associated with physico-chemical factors, especially with the seasonal variation of temperature and salinity Armi et al. Similarly, in Targus estuary, where air temperature, river flow and irradiance Algas diatomeas yahoo dating major drivers of seasonal phytoplankton patterns Gameiro et al.

Studies in tropical estuaries also suggest that seasonality influences phytoplankton composition, density and biomass: Our study was conducted in a shallow subtropical lagoonal system located in the coastal plain of the Rio Grande do Sul state, Brazil, which has a temporary connection to the Atlantic Ocean.

The hypothesis of this study is that the structure and dynamic of the phytoplankton and zooplankton in this system are controlled by the hydrodynamics and salinity as observed "Algas diatomeas yahoo dating" the other coastal lagoons from subtropical zones.

Therefore, our aim was to identify the spatial and seasonal changes of plankton in a subtropical lagoonal system and the relation between abiotic factors and community dynamics. The knowledge about microalgae in Peixe lagoonal system was limited to investigations about cyanobacteria WernerWerner and Sant'Annaand fossil diatom assemblage Santos Thus, the recognized ecological importance and the lack of research into plankton dynamics justify this study.

The lagoons are located in the Lagoa do Peixe National Park and its connection with the sea allows the migration of many species, making it an important refuge for the reproduction and feeding of fishes and crustaceans. This park is a major wetland conservation unit, being the only Ramsar site in Southern Brazil. Its maximum depth about 2 m is found near the mouth of the channel, which connects the lagoon to the sea.

Ruivo lagoon, a small oligohaline water body, is connected to the northern end of the Peixe lagoon Fig. The margins of the Peixe lagoon are covered by extensive salt marshes of Paspalum vaginatum Sw.

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These species are present with different vegetation associations in each sampling site Costa and TaglianiKnak Px-C is closer to the channel, less than 1. Ruivo lagoon is the farthest site from the sea about 19 kmconnected to the system through channels and wetlands to the northern area of the Peixe lagoon. L -1and oxidation-reduction potential - ORP mg. Depth and water transparency cm were measured with a Secchi disk.

We obtained these data on sampling dates including seven days prior. Laboratory analyses were performed as follows: L -1according to the Kjeldahl method NBRAlgas diatomeas yahoo dating, and total silicate mg.

Algas diatomeas yahoo dating -1 with the silico molybdate method APHA The classification of salinity was based on the Venice System Anonymous Trophic level was determined by the modified system of Vollenweider Wetzel Dominance and abundance were determined according to Lobo and Leighton Specific richness was estimated from the number of taxa at generic and infra-specific level, and species diversity was assessed using the Shannon index H ' Shannon and Weaver L -1 was calculated using Hillebrand's approximate geometric models Hillebrand et al.

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L -1 ; Wetzel and Likens The volume of analyzed material ranged from 0. The spatial and seasonal distribution of the sample units were related to abiotic factors using Principal Component Analysis PCA and Algas diatomeas yahoo dating 13 environmental variables.

A Monte Carlo permutation test was carried out to assess the significance of the ordination axes. The software Statistica r version 5. The software Pc-Ord r version 8. During the week of each seasonal sampling, precipitation was lower in spring and fall, 1. The wind direction in fall varied mainly from S to NW on sampling days. In winter, winds varied from NE to SW, with a predominance of southerly winds.

In spring, winds from the E quadrant prevailed, varying from NE to W. The highest hourly variation of wind direction was observed in summer.

However, winds were most persistent from the NE quadrant on sampling days.

The average wind velocities in winter and spring were 6. The channel was open throughout the year ofwhile in it was closed after the fall sampling, when Algas diatomeas yahoo dating small connection with the sea still remained.

The channel was artificially opened in early winter 2 Augustand remained open during the season. The connection of the lagoon with the ocean influenced the salinity of the system. The fall samples showed the highest saline waters uniformly throughout the system, and even Rvo and Px-S were mesohaline, while lower salinities and highest silicate and DO values were observed in winter. Concerning TP, the lagoon varied from eutrophic to hyper-eutrophic, except in Px-S where it was always hyper-eutrophic.

TN varied from predominantly mesotrophic to eutrophic in fall, winter and summer samples, and oligotrophic at all points in Algas diatomeas yahoo dating sample. The values of physical and chemical variables at the sample sites are shown in Table I. On the negative axis end we observed a spatial trend, where Px-C samples, closest to the channel, were grouped by salinity and conductivity.

On the positive axis end we observed a seasonal trend, with winter samples grouped at high values of DO and silica. The oxidation-reduction potential also contributed to the grouping of samples of Rvo.

Ordination diagram of the physical and chemical variables of different seasons in the Ruivo and Peixe lagoon. Legend for locations and variables see Table I.

The phytoplankton richness decreased from winter to summer samples Fig. Legend for locations see Table I. Phytoplankton density ranged from toind. In the fall, the environment was more homogeneous low Algas diatomeas yahoo dating and channel closing.

Spatially, the density was low in Px-C, close to the channel, independent of the season Fig. Phytoplankton biomass was highest at Px-C in fall samples due to a bloom of Euglena sp.

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The total phytoplankton density and biomass were not significantly correlated with any chemical variable, showing that the spatial and seasonal tendency of this dynamic environment was better explained by the variation of the species composition. The values of the specific diversity according to density and biomass showed little variation mean around 1.

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Diatoms and cyanobacteria were the most abundant groups in terms of density Fig. Only in fall samples the sites appeared to be spatially heterogeneous with a different dominant group at each sampling site. In samples from other seasons, we could see spatial resemblance in phytoplankton group composition, where Px-N and Px-S were similar in the warm seasons spring and summer.

However, in the winter samples, Px-N was more similar to Px-C, composed by diatoms, clorophytes and cyanobateria. Px-N and Px-S were dominated by cyanobacteria in spring, indicated by the correlation with chlorophyll a - blue 0.

In summer samples, cryptophytes Hemiselmis sp. Diatoms were the most abundant group at Px-C, in spring samples Asterionellopsis glacialis Castracane Round and Nitzschia sp.

The relative contribution of phytoplankton groups to biomass was similar to density, with some exceptions Fig. The most abundant groups were Euglenophyceae Algas diatomeas yahoo dating Bacillariophyceae, but Dinophyceae also played an important role.

Again, fall was the most heterogeneous season, but only at Px-C Euglena sp. L -1 remained dominant. L -1 was the dominant species at Rvo. In winter samples, the biomass pattern of the groups was the same as for density, with Chroococcus spp.

L -1 remaining dominant at Px-N, whereas for Px-C and Rvo sites the dominance was replaced by larger diatom Algas diatomeas yahoo dating, such as Diploneis didyma Ehrenberg Ehrenberg 0. L -1 and Surirella sp.

L -1respectively. In spring samples, Chroococcus Algas diatomeas yahoo dating. L -1 remained dominant at Px-N, correlating with chlorophyll a - blue 0. In summer samples, the dominance of dinoflagellates at Px-N and Px-S kept these points more similar. Asterionellopsis Algas diatomeas yahoo dating was the only species recorded at Px-C in samples from all seasons, and its biomass was correlated with conductivity 0. On the negative side of axis 1, high values of salinity, conductivity, chlorophyll a - brown, and Secchi transparency separated fall from the other seasons, however, the samples from Px-C were grouped by having their environment more influenced by the input of seawater through the channel.

This marine influence was indicated by Asterionellopsis glacialisa marine diatom that causes frequent blooms in the sea of southern Brazil.