An introduction to the benthos study in the High Paraná River

Abstract

This paper deals with the results of benthic studies carried out in the High Paraná River in the middle section, between the localities of Corpus and Itá Ibaté. Samples were collected monthly in the central area of the river channel from August 1977 to April 1980, using a Dietz-Lafond dredge, and filtered in the laboratory through 600 μm and 150 μm mesh opening screens. Occasionally, some samples were taken at particular sites, especially in marginal areas.
Analysis of the specific composition reveals a close relationship between the benthic fauna and the characteristics of the substrates: sandy, muddy, and rocky bottoms. In sandy bottoms, the species composition was very similar along the sampled reach, with numerical dominance of a species of Oligochaeta: Marapa posthiobris.
Remarkable variations were recorded across transversal and longitudinal sections (between 1,000 and 72,000 individuals per square meter), probably related to sediment granulometry and local current speed variations.Analysis of the spedfic composition reveals a close relation of the benthic fauna with the characteristics of the substrates: sandy, muddy and rocky bottoms. In sandy bottoms the specific composition was very similar along the sampled reach, with numerical dominance of a species of Oligochaeta: Narapa bonettoi. Remarkable variations were registered through transversal and longitudinal sections (between 1.000 and 72.000 individuals per square meters), probably related to sediment granulometry and local current speed variations.