POLYCHAETE (ANNELIDA) COMMUNITIES UNDER THE INFLUENCE OF OIL SPILLS AND THEIR DERIVATIVES AT TODOS OS SANTOS BAY, BAHIA, BRAZIL
Peso-Aguiar, M. C.1, Santa-Isabel, L. M.1,2, Jesus, A. C. S.1, & Dutra, L. X. C.1,2
1 Universidade Federal da Bahia, Instituto de Biologia, Departamento de Zoologia, Campus Universitário de Ondina, s/n. CEP. 40170-290, Salvador, BA, Brazil
2 Laboratório de Estudos Costeiros - PPPG- IGEO-UFBA, Rua Caetano Moura, 123, Federação, CEP. 40170-290, Salvador, BA, Brazil
The environmental stress under which the coastal zone is imposed causes alterations in the structure of the aquatic communities. It results in a constant disequilibrium of these ecosystems. This study aims to characterize qualitatively and quantitatively the intertidal polychaete communities under industrial activities such as refinery, transport terminal and transport lane and extraction of petroleum from the northwestern portion of the Todos os Santos Bay. Random samples were taken in an impacted area in February, May, September and December 1994 and March, June, September and December 1995, using 30 quadrats of 0.09 m2; a control area, with no impact, was sampled in the same period. Polychaetes were anesthetised in the field, using 7.5% MgCl2, followed by fixation with 4% formaldehyde solution and preservation in 70% ethanol. A total of 2,853 specimens were collected. The average density was 132.8 ind/m2, with a dominance of 92% for the polychaetes when compared to the other taxa recorded such as Nemertini, Mollusca and Arthropoda. Among the 29 species recorded, only Laeonereis acuta, Capitella capitata and Sigambra grubii were present in all samples. L. acuta had an average density of 93.1 ind/m², corresponding to 70% of the abundance in the polychaete communities. Seasonal fluctuation, with peaks in the spring and summer, suggests an oportunistic behavior for this species. C. capitata represented 14% and S. grubii 4.4% of the polychaetes sampled, respectively. Cluster analysis of the results on density and occurrence of the species recorded in the samples revealed a higher similarity among the temporal density than among the seasonal occurrence of species in the community. Comparison with the control station, which showed no dominance of opportunistic species, these results indicate that the polychaete worms were the best colonizers under the environmental conditions imposed by the derivatives spilled by the refinery.