Species richness and distribution of oligochaetes in six reservoirs on Middle and Lower Tietê River (SP, Brazil)

SURIANI, A.L.; FRANCA, R.; ZAITUNE PAMPLIN, P.; MARCHESE, M. R; DE LUCCA, J.V.; ROCHA, O.

Acta Limnologica Brasiliensia

Sociedade Brasileira de Limnologia

Lugar: San Pablo, Brasil; Año: 2007 vol. 19

0102-6712

The objective of this study was to determine the structure of the Oligochaeta populations in six reservoirs located in the Middle and Low section of 'rtere Rl ver. Sampling was carried out in November 2002, in the rainy season, and in August 2003, in the dry season. In each reservoir, three transects were established: upper, middle and lower (near dam). Duplicate samples were collected with a van ve.en grab which sampled an area of  337.0 ern". Seventeen oligochaetes species were identified, A gradient was observed in the number of species per reservoir, which diminished steadily from Barra Bonita to Tres trrnaos dam. Branchiura sowerbyi was the dominant specie in every reservoir from Bariri (58.57%) down to Nova Avanhandava (92.16%), being outnumbered only in Barra Bonita, where Limnodrilus hoffmeisteri was dominant, representing 59% of the oligochaetes recorded. The highest average total densities, 470 ±a 205 md.m? in November 2002 and 260 ±a 123 irrd.rn" in August 2003, were recorded in the Bariri reservoir, The average density, as the species richness, of oligochaetes tended to diminish downstream towards Tres rrrnaos. where the densities varied between 18 ±a 6 ind.m? (November 2002) and 30 ±a 12 irid.rn" (August 2003). The grouping of the reservoirs on the basis of oligochaetes density and on the climatic periods joined the reservoirs in accordance with its geographic sequence throughout the river and also reflected their trophic state. The abundance and diversity of oligochaetes reflect the trophic state of the reservoirs and can therefore be used as a biological indicator of trophic state conditions. ve.en grab which sampled an area of  337.0 ern". Seventeen oligochaetes species were identified, A gradient was observed in the number of species per reservoir, which diminished steadily from Barra Bonita to Tres trrnaos dam. Branchiura sowerbyi was the dominant specie in every reservoir from Bariri (58.57%) down to Nova Avanhandava (92.16%), being outnumbered only in Barra Bonita, where Limnodrilus hoffmeisteri was dominant, representing 59% of the oligochaetes recorded. The highest average total densities, 470 ±a 205 md.m? in November 2002 and 260 ±a 123 irrd.rn" in August 2003, were recorded in the Bariri reservoir, The average density, as the species richness, of oligochaetes tended to diminish downstream towards Tres rrrnaos. where the densities varied between 18 ±a 6 ind.m? (November 2002) and 30 ±a 12 irid.rn" (August 2003). The grouping of the reservoirs on the basis of oligochaetes density and on the climatic periods joined the reservoirs in accordance with its geographic sequence throughout the river and also reflected their trophic state. The abundance and diversity of oligochaetes reflect the trophic state of the reservoirs and can therefore be used as a biological indicator of trophic state conditions.