THE ECOLOGY OF LAEONEREIS ACUTA (TREADWELL, 1923) (POLYCHAETA: NEREIDIDAE) IN THE ESTUARIES OF THE SERGIPE AND PIAUÍ RIVERS (NORTHEASTERN BRAZIL)
Couto, E. C. G. & Fernandes, A. C. M.
Departamento de Biologia, Universidade Federal de Sergipe, J. Rosa Elze, 49100-000, São Cristóvão, SE, Brazil
Unvegetated tidal flats in estuarine waters of Sergipe and Piauí Rivers are characterised by the presence of a typical macroinfaunal assemblage dominated by the polychaetes Laeonereis acuta and Capitella capitata and the bivalve Anomalocardia brasiliana. Although data on densities can be found in the literature, the dynamics of this particular assemblage is poorly known. Benthic macroinfaunal populations were monitored from July 1993 to July 1994 using a corer (15 cm in diameter). Samples were processed through 250 um mesh and the material going through the mesh was sorted under a binocular microscope to count the smaller-sized. In this work we present the population structure, seasonal dynamics and production of the polychaete Laeonereis acuta in the Praia Formosa and Ilha do Caibro areas. Praia Formosa receives domestic and industrial wastes. The abundance of this species was shown to be influenced by silt-clay and organic matter contents and by salinity. The species occurred at high densities in Winter, 1993 in the R. Piauí (152 inds. 0.09 m-2) and in Summer, 1994 in the Sergipe River (262 inds. 0.09 m-2). The species shows an extended spawning season with constant recruitment throughout the year, although peaks of recruitment were detected at the end of summer (February to April) in the Sergipe River and in Winter (July to September) in the Piaui River. A sharp decrease in densities was registered in December and January in both areas. Laeonereis acuta was absent in May and July 1994 in the Piaui River and August, October, November and December 1993 in the Sergipe River. Biomass data ranged from 0.05 g. 0.09 m-2 in June 1994 to 6.50 g. 0.09 m-2 in August 1993 for the Piaui River and 0.12 g. 0.09 m-2 in July 1993 to 7.12 g. 0.09 m-2 in June 1994 for the Sergipe River.