La composition et la distribution spatio-temporelle des micro-algues de quatre rivières du Sud-est de la Côte d'Ivoire (Soumié, Eholié, Ehania et Noé) ont été analysées, en relation avec des paramètres physicochimiques du milieu. Méthodologie et résultats : La zone pélagique et les supports littoraux (pierres, feuilles et bois) ont été échantillonnés en amont et en aval de chaque rivière. Au total, 192 taxons spécifiques et infraspécifiques ont pu être identifiés, parmi lesquels environ 75 % d'espèces de Diatomées, 10,4 % de Cyanobactéries, 9,9 % de Chlorophytes, 4,2 % d'Euglénophycées et 0,5 % de Rhodophycées. Les Diatomées constituent la classe la plus constamment rencontrées dans les prélèvements des quatre cours d'eau De plus les algues périphytiques sont plus diversifiées que celles de pleine eau. Les espèces Gyrosigma acuminatum, Nitzschia palea, Ulnaria biceps et Gomphonema parvulum sont communes à tous les habitats explorés. Conclusion : Les variations de la composition des peuplements entre les rivières sont relativement faibles, avec des diversités plus importantes dans la rivière Noé (134 taxons) et peu élevées dans la rivière Ehania (127 taxons). En outre, les algues récoltées sur feuille et sur bois présentent une forte similarité dans tous les cours d'eau prospectées.
The objective is to study the phytoplankton community of Dohou Lake in order to contribute to the knowledge of its ecological quality. For this purpose, monthly samplings were carried out annually between October 2017 and September 2018. The studied physicochemical parameters (Temperature, Electrical conductivity, pH, Dissolved oxygen, Transparency, Depth, Total nitrogen, Nitrate, Nitrite, Total phosphorus) varied significantly over time. During the rainy season months, Dohou Lake is influenced by high values of total phosphorus, total nitrogen, conductivity, nitrate, pH, transparency and depth. However, in the dry season, the lake is characterized by high values of temperature, nitrite, dissolved oxygen and conductivity. For the phytoplankton community, 373 phytoplankton taxa divided into 111 genera, 51 families, 24 orders, 11 classes and 7 phyla (Chlorophyta, Euglenophyta, Cyanobacteria, Bacillariophyta, Pyrrophyta, Chrysophyta and Xanthophyta) have been identified. Chlorophyta with 50.67% is the most represented in the taxonomic richness of the environment. Total phytoplankton densities oscillate between 100 105 cells / L (August) and 321 105 cells / L (February) with high proportions of Cyanobacteria greater than 45% during each month of the rainy season. The highest values of Shannon and Equitability diversities are observed during the dry season months.
The aim of the present study was to contribute to knowledge of the freshwater epilithic diatoms flora of Cote dIvoire. Diatoms were sampled in February and July 2012 on glass slides previously immersed during a period of 30 days at ten stations.The species composition of new and rare taxa was compiled, accompanied by illustrations. Forty two taxa distributed among 16 genera, 8 families and 5 orders were recorded in the temporal survey.Based on species occurrence frequency, 32 rare, 2 occasional, and 8 common species were registered. According to geographic distribution, taxa recorded were mostly cosmopolitan (47.72%) and tropical (43.18%), while 9.09% were endemic.Taking into account their affinity towards pH, 3 classes of diatoms : acidophilic taxa (35.47%), indifferent taxa (59.52%) and alkaliphilic taxa (4.76%)were found in the Me River.
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