Effects of an experimental in situ diesel oil spill on the benthic community of unvegetated tidal flats in a subtropical estuary (Paranaguá Bay, Brazil).

The effects of diesel oil on benthic associations from unvegetated tidal flats in a subtropical estuary were experimentally evaluated using a Multivariate Before and After/Control and Impact Model (M-BACI). Impacted treatments were contrasted with controls in 14 successive periods before and after the oil spill. An acute effect was recorded just after the impact, but the recovery to pre-disturbance population levels was extremely fast. The increase in the total density of the benthic community after the disturbance was the result of an increase in the densities of Heleobia australis, oligochaetes, and ostracods, observed in both impacted and control treatments, as a reflection of background variability and not the presence of the contaminant. The experimental spill had little influence on the biological descriptors of the benthic associations, which were resilient or tolerant to oil disturbance at the temporal (147 days) and spatial (cm²) scales used in the experiment.