El Bentos del Parana Media en el tramo Corrientes-Esquina

Resumen

Quali-quantitative variations of the benthos from the Middle Paraná river course, were studied. Spatial and temporal distribution was analyzed in relation with the main environmental factors.

Studies were monthly carried out during March 1981-March 1982 in four stations near the localities of Comentes, Bella Vista, Coya and Esquina. In each of them, four sampling points were stablished in the cross sections of the river. Samples were obtained with a Dietz-LaFond dredge and fíltered through 500 and 150 µm mesh opening screens. The predominant sandy bottoms are inhabited by a specialized psammophilous fauna. The community structure was similar along all the studied stretch. Abundánce was very fluctuant, with maximun valúes of 160.000 ind/m2 with a strong numerical dominance of a species of Oligochaeta: Narapa bonettoi Correlations análysis showed a positive association between the mean grain size and the total abundance. These coeflcients were signiñcatives in all the stations for microturbellarians but only in Goya and Esquina for N. bonettoi

Clay bank substraía from the river margins had a richer but less abundant fauna (maximun valúes of 29.000 ind/m2) with predominance of Xenochironomus sp. The benthos of the soft silty bottoms was the least diversé and abundant.

Seasonal changes in the abundance were observed. There was an increment in spring and the early summer with a tendency to decrease during summer floods. This pattem was similar in the thxee kinds of bottoms, but more evident in the soft silty ones.