THE EPIPHYTIC ALGAE ON FLOATING MACROPHYTES OF A PARANA RIVER FLOODPLAIN LAKE

We describe the composition and seasonal (1993-1994) changes of epiphy tic algae on the submerged parts of macrophytes (Eichhornia crassipes (Mart.) Solms-Loubach, Salvinia rotundifolia Willd., Lemna gibba L. an d Ricciocarpos natans (L.) Corda) of a shallow lake from Entre Rios pr ovince, Argentina (33 degrees 48'S, 58 degrees 57'W), permanently conn ected to the Parana river. In total, 136 algal taxa were identified: 5 7 Bacillariophyceae, 31 Chlorophyta, 31 Cyanophyceae, 13 Tribophyceae and 4 Euglenophyceae, all of them characterized by wide geographic dis tributions. Infertile filaments of Oedogonium spp., Zygnema spp., Spir ogyra spp, and Mougeotia spp. (Chlorophyta) dominated the assemblages throughout the year. The diatoms Eunotia bilunaris var, bilunaris, E. monodon var. monodon and two varieties of Gomphonema augur reached hig h relative frequencies. Characiopsis ettliana and Ch. fair var. cecoal ensis (Tribophyceae) were consistently present in low numbers. Multiva riate analyses did not reveal major compositional dissimilarities betw een the four substrates surveyed. Seasonal changes in the community co mposition were chiefly due to the presence of thychoepiphytic species in association with the interchange of river and lake waters. It is co ncluded that the pattern of seasonal succession is governed by a compl ex interaction between hydrometric and seasonal changes.