Author(s): Seu-Anoï NM, Niamien-Ebrottié JE, Komoé K and Ouattara A

Abstract: Present study was conducted to determine the pelagic diatoms and factors that influence their dynamics in the Aby lagoon system, southern-central Ivory Coast for one annual survey period (2006-2007). The phytoplankton was collected using a plankton net (mesh size: 20 μm) tied unto a motorized boat and towed slowly for five minutes at 13 different stations. Overall, a total of 69 diatom taxa belonging to 28 genera and three families were recorded. From a generic point of view, 22 taxa were pennates while six were of centric forms. Multivariate analysis showed that there were significant positive and negative relationships (P<0.05) between some physicochemical parameters and diatom species in this lagoon. The results of Redundancy analysis (RDA) showed that some taxa such as Ulnaria biceps, Gomphonema gracile, Gomphonema parvulum, Gomphonema sp., Pinnularia viridis, Navicula lanceolata, Navicula heimansioides, Navicula cf. peregrina and Aulacoseira islandica were closely associated with soluble reactive Si (SRSi) and temperature whereas the determining factors for Ulnaria sp.1, Ulnaria sp.2, Frustulia rhomboides, Gyrosigma cf. balticum and Nitzschia sigma were salinity and pH. Other taxa, Actinocyclus sp., Aulacoseira granulata, Aulacoseira granulata var. angustissima, Aulacoseira granulata var. curvata, Cyclotella meneghiniana, Cyclotella ocellata and Tryblionella levidensis were closely associated with NO3- and soluble reactive phosphate (SRP).

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