Influência da eutrofização do Complexo Estuarino-Lagunar Mundaú/Manguaba, Alagoas-Brasil sobre a comunidade fitoplanctônica

As lagunas Manguaba e Mundaú, juntamente com os canais que as interligam constituem o Complexo Estuarino-Lagunar Mundaú/Manguaba (9° 34 38 9° 45 30 S e 35° 44 00 35° 58 13 W), o mais produtivo ecossistema aquático do estado de Alagoas. Essas lagunas foram investigadas, visando relacionar a estrutura e dinâmica da comunidade fitoplanctônica com o seu estado trófico e parâmetros ambientais. Coletas de material fitoplanctônico e para análise físico-químicas foram realizadas em 8 estações fixas, durante maré vazante e enchente nos períodos chuvoso (maio a julho/2002) e seco (setembro e novembro/2002). Amostras foram coletadas com garrafas de Van Dorn para o estudo da densidade fitoplanctônica (preservadas com lugol), clorofila a e variáveis físico-químicas e rede de plâncton com 45µm de abertura de malha, para o estudo do microfitoplâncton (preservadas com formol neutralizado a 4%). Foram também realizados experimentos de enriquecimento com as espécies bioindicadoras Microcytis aeruginosa (Kützing) Kützing e Anabaena spiroides Klebahn. O regime de salinidade variou de mesoalino a limnético na Laguna Mundaú e de Oligoalino a limnético na Laguna Manguaba. A transparência da água foi maior no período seco. Os teores de oxigênio dissolvido estiveram entre 1,7 ml.L-1 e 7,8 ml.L-1, com taxas de saturação entre saturado e supersaturado. As concentrações de nutrientes dissolvidos apresentaram amplas variações, sendo significativamente mais elevadas no período chuvoso. Apenas o nitrato não apresentou diferença significativa com relação aos períodos estudados. A razão N:P foi mais elevada no período chuvoso, porém, sempre inferior a 16:1 e o índice de estado trófico (IET) classificou as lagunas como eutróficas e hipereutróficas nos dois períodos. A densidade fitoplanctônica total variou entre 110.000 Cél.L-1 a 9.915.000 Cél.L-1 e a clorofila a entre 4,2 mg.m3 a 221,8 mg.m3. Foram identificados 155 táxons, predominando a divisão Bacillariophyta. A espécie mais abundante e freqüente na Laguna Mundaú foi a diatomácea Skeletonema costatum (Greville) Cleve e na Laguna Manguaba foi a diatomácea Cyclotella meneghiniana Kützing e as cianofíceas Microcystis aeruginosa e Anabaena spiroides. Os indicadores biológicos de eutrofização foram as cianofíceas Anabaena spiroides, Microcytis aeruginosa e Skeletonema costatum que constituíram blooms durante todo ano, indicando elevado processo de eutriofização nas duas lagunas. A diversidade específica e a equitabilidade foram mais altas no período chuvoso. Os valores de diversidade oscilaram entre 0,17 bits Cel.L-1 e 4,81 bits Cel.L-1. A predominância das espécies dulciaquícolas, (51%), evidenciou a maior influência do fluxo limnético no ambiente estudado. Os resultados dos bioensaios demonstraram que o fosfato foi o nutriente que governou o crescimento das microalgas Anabaena spiroides e Microcytis aeruginosa, sugerindo, que as florações das referidas microalgas nas lagunas Mundaú e Manguaba estão sendo ocasionadas, provavelmente, pelo elevado teor deste nutriente no ambient

Microphytoplankton biomass and trophic state of the Estuarine Region of São Francisco River (northeastern Brazil)

One of the most serious problems that affect estuaries is the excessive enrichment of nutrients, especially nitrogen and phosphorus compounds that result in increased productivity. Studies to evaluate the trophic conditions of the São Francisco River estuary were conducted at four stations in the rainy (July/ 2006 ) and dry (January/2007) season in neap and spring tides, during high tide and low tide. Microphytoplankton was collected using plankton nets with mesh size of 45mm and the samples for analysis of nutrients and Phytoplankton biomass (chlorophyll a) were obtained from the sub-surface layer with wide-mouthed plastic bottles. The waters of this ecosystem showed salinities ranging from an oligohaline to a limnetic regime, alkaline pH and water clarity ranging between 1.00m and 2.60m. The concentrations of dissolved nutrients varied considerably, being highest during the dry season period. The Microphytoplankton was composed of 176 taxa, mainly distributed among the Chlorophyta, Charophyta and Bacillariophyta. Phytoplankton biomass (chlorophyll a) showed no significant differences between seasons, tides and tidal regimes, however the density (Cel.L-1) was significantly higher in the dry season. Values of a TSI showed oligotrophic conditions in the four stations and in the two periods analyzed. In the dry season there was a higher cell density and increased levels of dissolved nutrients with the exception of nitrate that was considered higher in the rainy season. The Microphytoplankton species are characteristic of waters of low to moderate trophic level and the TSI indicated a predominance of oligotrophic conditions in the two seasons in the study area.Keywords: chlorophyll a, estuary,  hydrology, phytoplankton, seasonality 

Phytoplankton community structure of the São Francisco river estuary (Piaçabuçu-Alagoas-Brazil): a study of its diversity

Studies aimed at determining phytoplankton composition, biomass, ecology and some physical-chemical characteristics of the São Francisco estuary were conducted at 7 sampling stations located in Piaçabuçu-Alagoas (10º25’-10°30’S and 36º23’-36º27W) during the rainy and dry seasons. The samples were obtained from the subsurface layer at neap and spring tides, during high and low tides, using a plankton net with 45 um mesh size. The waters from this estuary are characterized by low salinity, high temperatures, pH between alkaline and slightly acid, transparency greater than 1 meter. The phytoplankton was composed of 205 taxa, mainly distributed between the divisions Chlorophyta and Bacillariophyta, considered the most representative. The diatom Aulacoseira ambigua was considered dominant. Most of the species identified were planktonic and of freshwater origin. Specific diversity and equitability were considered average and high, indicating conditions of environmental equilibrium in the studied area. The analysis of variance in taxonomic richness revealed higher averages for the dry season and for high tides. Chlorophyll a content ranged between 0.4ug/L and 24,4ug/L. The annual variation of phytoplankton and physical-chemical parameters was related to rainfall.Studies aimed at determining phytoplankton composition, biomass, ecology and some physical-chemical characteristics of the São Francisco estuary were conducted at 7 sampling stations located in Piaçabuçu-Alagoas (10º25’-10°30’S and 36º23’-36º27W) during the rainy and dry seasons. The samples were obtained from the subsurface layer at neap and spring tides, during high and low tides, using a plankton net with 45 um mesh size. The waters from this estuary are characterized by low salinity, high temperatures, pH between alkaline and slightly acid, transparency greater than 1 meter. The phytoplankton was composed of 205 taxa, mainly distributed between the divisions Chlorophyta and Bacillariophyta, considered the most representative. The diatom Aulacoseira ambigua was considered dominant. Most of the species identified were planktonic and of freshwater origin. Specific diversity and equitability were considered average and high, indicating conditions of environmental equilibrium in the studied area. The analysis of variance in taxonomic richness revealed higher averages for the dry season and for high tides. Chlorophyll a content ranged between 0.4ug/L and 24,4ug/L. The annual variation of phytoplankton and physical-chemical parameters was related to rainfall

Expansion of invasive Ceratium furcoides (Dinophyta) toward north-central Brazil: new records in tropical environments

Abstract: Aim We record new occurrences of the invasive species Ceratium furcoides in reservoirs and their affluents in the Paraná River basin, State of Goiás (GO), central-western Brazil, and in some localities in the São Francisco River basin, northeastern region. Methods Qualitative and quantitative phytoplankton samples were collected from Corumbá Reservoir and Cascatinha Falls, Caldas Novas, GO, and João Leite Reservoir, Goiânia, GO, both in the Paraná River basin, and samples from the São Franscisco River basin. Specimens of C. furcoides were observed with optical, epifluorescence and scanning electron microscopy. Results The individuals of C. furcoides from these environments agreed morphologically with populations in other reservoirs in Brazil and other locations, especially concerning the tabulation and the shape of the fourth apical plate. These environments ranged from oligotrophic to eutrophic conditions. Physical and chemical variables of these waterbodies, compared to other environments where this species was found, demonstrate that C. furcoides is a highly eurytopic species. The dispersal pattern of C. furcoides seems to be more complex than upstream-downstream regulation, since the species occurs in high-altitude environments and systems upstream from previously recorded locations. Conclusion An analysis based on the areas of occurrence and the chronology of the records demonstrated that C. furcoides has spread toward northern Brazil. Studies of the relationships among populations recorded in other parts of Brazil and South America are required in order to develop accurate models of dispersal for this invasive species, and will facilitate the development of management policies for aquatic systems in Brazil