COMPOSITION AND DISTRIBUTION OF POLYCHAETES IN THE BEACH INTERTIDAL REGION OF THE SÃO SEBASTIÃO CHANNEL (SÃO PAULO, BRAZIL)
Rizzo, A. E.1 & Amaral, A. C. Z.2
1Universidade Estadual Paulista -UNESP - Pós-graduação em Zoologia. Av. 24-A, 1515, Rio Claro, SP, 13506-900, Brazil
2Universidade Estadual de Campinas - IB/Depto. de Zoologia, C.P. 6109, 13083-970, Campinas, SP, Brazil
The spatial-temporal distribution and faunal composition of polychaetes from São Francisco and Engenho D'Água beaches in the São Sebastião Channel were studied. This region is subject to oil spillage from an oil terminal and untreated domestic sewage waste. The substrate of the study sites is sand and varying sized stones. The São Francisco site is exposed to domestic sewage drainage. Samples were collected monthly from August 1995 to July 1996, in two 10 m wide transects, divided into three parallel strata (lower, intermediate, and upper) from the shore. A total of 180 samples were taken per transect using a cylindrical, 0.01m2 diameter, 20cm long, sampler. Granulometry, calcium carbonate and organic matter concentrations, salinity, sediment temperature, and fecal coliform bacteria were quantified and used for discriminating single-species distributions. Polychaetes were well represented in most samples, and species diversity increased with increasing substrate heterogeneity. Forty eight species were recorded from São Francisco and 43 from Engenho D'Água; the latter, however, showed higher species equitability and diversity. Species richness increased with decreasing distance from the shore. In Engenho D'Água the spatial and temporal species distributions were more homogeneous than in São Francisco. The most abundant species in Engenho D'Água, Nematonereis hebes, Cirriformia filigera and Scyphoproctus djiboutiensis, occurred at the intermediate and lower interdital regions during summer and fall. The upper intertidal zone of São Francisco, closest to the sewage discharge, was characterized by opportunistic species each at high densities and low dominance; the principal species being Capitella capitata, Scolelepis squamata and Laeonereis acuta, as well as tubificid oligochaetes. The capitellids, C. capitata, Heteromastus filiformis and Capitomastus minimus, together with the oligochaetes, were summer dominants, while L. acuta and S. squamata were winter dominants. In October 1995, opportunistic species did not occur in São Francisco, resulting in a higher diversity and equitability. The observed polychaete community heterogeneity in São Francisco is an evidence of the strong influence of organic enrichment on single-species distributions.