Contribución al conocimiento del fitoplancton del Paraná Medio.

Resumen

Structure, population density and distribution of the Middle Paraná River phytoplankton -from Corrientes to Esquina- during a period of 13 months (March 1981 to March 1982) were considered in this paper. Transversal and longitudinal variations experimented by the phytoplankton and its relation with environmental fáctors, are also discussed. Qualitative and quantitative sub-superfidal samples were monthly obtained in three points of the river (centre, right and left margin) in 4 sampling stations (Corrientes, Bella Vista, Goya and Esquina). Counts were done by the Utermohl method with an inverted microscope. The phytoplankton community was dominated by Diatomophyceae (mainly Melosira granulata and M. pseudogranulata) and Chlorophyceae (mainly Monoraphidium spp. and Scenedesmus spp.). Among Cyanophyceae, Raphidiopsis mediterranea, Lyngbya limnetica and Anabaena spiroides were the dominant. Euglenophyceae, Ciyptophyceae, Dinophyceae and Chrysophyceae were scarcely represented. Variations in the phytoplankton community were related with different contributions of the High Paraná and Paraguay Rivers and the Progressive influence in downstream direction of the Middle Paraná floodplain.