Variação da composição, distribuição espacial e influência dos fatores ambientais sobre a ocorrência de Characeae (Chlorophyta) em um reservatório subtropical

Abstract

The family Characeae, represented in Brazil by the genera Chara and Nitella, is considered the closest living relatives of terrestrial plants and play several ecological roles, such as the increase of water transparency and habitat complexity. This research aimed to verify the composition and structure of Characeae community at Itaipu reservoir (24°05´S e 25°33´S; 54°00´W e 54°37´W), formed in Parana river, relating them to simple environmental variables, such as conductivity, water transparency and fetch. Samples were collected in eight arms of rivers that form the Brazilian side of the reservoir (Arroio Guaçu, São Francisco Verdadeiro, São Francisco Falso, São Vicente, São João, Ocoí, Pinto e Passo Cuê). A total of 17 taxa were identified, of which Chara hydropitys Reichenbach, C. rusbyana Howe, Nitella axillaris A. Braun, N. glaziovii G. Zeller, N. gracilis (Smith) C. Agardh, N. hyalina (DC) C. Agardh, N. inversa Imahori and N. microcarpa Braun, represent new citations in the Itaipu Reservoir and Paraná State. Chara guairensis, Nitella furcata and Nitella glaziovii showed the largest geographical ranges, while Chara hidropytis and Chara rusbyana showed more restricted distribution. Furthermore, it was found that among the environmental factors considered important for the establishing of charophytes at the tributaries of the reservoir, the underwater radiation positively affects the occurrence of the genera Chara and Nitella, while fetch values showed negative influence on the occurrence of genus Nitella during the period analyzed.