The arm of this study was to avaluate the structure of the Benthic Macroinvertebrate
assemblage an annual cycle in the Xingu River system, Brazil, measuring the annual
secondary production. Two environments were studied in the middle Xingu River: the
main channel and an insular lake. In the Lake were investigate the marginal and
deeper habitats, with an Ekman-Birge grab. The habitats studied in the main channel
were the rapids and the low flowing waters, with a surber net and corer. Were
collected 23,432 macrobenthic orgamisms of 43 taxa, 8 classes and 4 phyla. The
insects and gastropods compose the 47% and 36% of the total individuals collected,
respectively. Rapids show the main taxa diversity. The fluvial low flowing and the
marginal lake environments were very similar in species number. The mean density
during the low waters was 1,605.75 ind.m-2, and during the flooding season was
894.43 ind.m-2. Leptophlebiidae, Hydropsychidae and Chironomidae were,
respectively, the most relative abundants in the River with 29,0%, 21,4% and
13,07%. However, in the Lake Chironomidae (34,6%), Oligochaeta (23,2%),
Chaoboridade (14,7%) and Nematoda (14,5%) were the most relative abundants.
The macroinvertebrate assemblages differences between habitats were related with
oxygen deficit in the waters and nutrients dissolved. The rapids were the more
dissimilar habitat between all studied.
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