Resumen

BERTRAN, CARLOS; ARENAS, JOSÉ  y  PARRA, OSCAR. Macrofauna of the lower reach and estuary of Biobío river (Chile): changes associated to seasonal changes of the river flow. Rev. chil. hist. nat. [online]. 2001, vol.74, n.2, pp. 331-340. ISSN 0716-078X.  doi: 10.4067/S0716-078X2001000200010.

The Biobío river (ca. 37º S) is one of the most important Chilean lotic systems with regard to their water flow. Its estuary is reduced, especially during maximum flow. With the purpose of testing the hypothesis that during summer, the decrease of river flow results in a higher deposition of fine particles, and that the increase in river flow during winter results in the washing and transport of deposited particles, and consequently in a decrease of the benthic macrofauna. Sediment samples were collected for sedimentological and faunistical analysis during August 1993 and March 1994. The sedimentological analyses indicate that mean size of sediment corresponded to coarse sands. During summer, the deposition of suspended particles is facilitated by the decrease in the river flow and results in higher percentage of fine particles and organic matter in the sediment. The benthic macrofauna was composed by 16 taxa during winter and 42 taxa during summer. During winter, that macrofauna was represented by just a few individuals. During summer, the species richness and macrofaunal abundances increased. The most abundant taxa were an archiannelid species and the polychaete Perinereis gualpensis. The increase of river flow during winter determines the transport of the deposited material toward the sea and consequently, the washing of benthic organisms. Even though, values of macrofaunal abundance and biomass during summer were about one order of magnitude higher than during winter, they are still lower than those mentioned for other estuaries of south-central Chile (ca. 39º S). That confirms the atypical character of the Biobío river estuary, which due to its seasonal changes, significantly affects the community structure of the benthic macrofauna

Palabras clave : macrofauna; Biobío river estuary; changes of river flow.