Horizontal distribution and temporal variation of the zoobenthos of a
tropical Brazilian lake
CLETO-FILHO1, S.E.N. & ARCIFA1, M.S.
1 Departamento de Biologia, FFCLRP-USP, Av. Bandeirantes 3900, 14040-901 Ribeirão Preto – SP, Brazil.
e-mail: scleto@usp.br; marcifa@usp.br
ABSTRACT: The community of benthic macroinvertebrates of Lake Monte Alegre (Ribeirão Preto, SP, Brazil) was studied from March 2001 to December 2002. Zoobenthos samplings and measurements of physical and chemical factors, such as temperature, dissolved oxygen, electrical conductivity, and pH of the water column, were carried out every three months in two transects (longitudinal and transversal) at 1, 2, 3, 4 and 5 m depths. The same physical and chemical factors were also measured every month in the water column at the maximum depth (5 m). Granulometry and organic matter content of the sediment were also analyzed twice at each transect. More stable thermal stratification was established in the lake during the warm season and periods of total circulation occurred during the cool one. Temperature, dissolved oxygen, coarse particles of the sediment decreased, whereas electrical conductivity, fine particles and the relative organic matter content increased toward the deep region. The distribution pattern of benthic organisms, expressed in densities and biomass, was similar in both transects, with dominance of Chaoboridae (Chaoborus brasiliensis) in the deep zone and Chironomidae in the shallow one. Biological (diversity, richness, evenness and similarity) indices reflected the distribution pattern with higher richness and diversity in the shallow zone of the lake, mostly influenced by Chironomidae.
Key-words: benthic macroinvertebrates, Lago Monte Alegre, tropical lake, Chaoboridae, Chironomidae.