Effects of hydrocarbon pollution in the structure of macrobenthic assemblages from two large estuaries in Brazil.

Changes in the structure of benthic macrofauna and its relationship with hydrocarbon contamination were determined at different spatial scales in sublittoral sediments of two large estuaries in Brazil. Guanabara Bay (GB) is a heavily polluted estuary due to the presence of a large industrial complex and high demographic density. Laranjeiras Bay (LB) lies in an Environmental Protection Area and can still be considered as preserved from human activities. Despite some spatial differences within each bay, the PAHs concentrations were significantly and consistently higher in GB, with values generally above the threshold effect levels. No signs of hydrocarbon contamination were observed in LB. Macrofauna abundance, diversity and overall assemblage structure were largely different between bays. Canonical analysis of principal coordinates (CAP), used to model the relationship between macrofauna and PAHs levels, indicated that this class of hydrocarbons is the main structuring factor of soft-bottom assemblages in both bays.

Are changes in the structure of nematode assemblages reliable indicators of moderate petroleum contamination?

This study assesses through a multiple before-after-control-impact (MBACI) design the effects of diesel oil on the structure of nematode assemblages in unvegetated tidal flats of a subtropical estuary. Oil-exposed treatments were contrasted with controls for a duration of four successive days before and after an experimental spill in three distinct areas of the Paranaguá Estuarine Complex (Southern Brazil). No significant differences were observed in nematode total density, number of taxa and the overall assemblage structure between the control and impact treatments from before to after the experimental spill. This reinforces the idea that, despite being good indicators of environmental stress, free-living marine nematodes are able to tolerate low concentrations of hydrocarbons and to survive in moderately contaminated areas. We also show that robust experimental designs are useful to avoid confounding expected natural variability with the effects of a mild impact.