Deep-sea meiofauna response to synthetic-based drilling mud discharge off SE Brazil

The response of the meiofauna communities to the discharge of synthetic-based mud (SBM) cuttings from an exploratory drill was analyzed in a deep-sea site (mean depth of 890 m) in the Campos Basin, southeast Brazil. A total of 159 samples were taken on three sampling cruises: one pre- and two post-drilling (1 month and 1 year after drilling). One month after drilling, significant decreases in the meiofauna density and number of taxa were observed, as well as in nematode density and richness (number of families and genera); conversely, relative abundances of non-selective deposit-feeding nematodes, particularly the genus Sabatieria, increased significantly. Univariate and multivariate analyses indicate that the impacts on meiofauna were not restricted to a potential area of impact predicted by a model of cuttings dispersal; meiofauna changes just after the drilling agreed with the model in showing northward dispersal but over a larger area. The meiofauna, however, showed a weak correlation with the analyzed chemical parameters, such as hydrocarbon and metal concentrations. The results suggest that the effects of SBM drill cutting discharge on the meiofauna were probably related to physical changes in the substrate. Twelve months after drilling, most of the values of the meiofauna descriptors had returned to pre-impact period values. Nonetheless, the multivariate structure of meiofauna community was still significantly different, and the number of meiofauna taxa, densities of copepods, and epigrowth-feeder nematodes increased significantly. The increase of superficial forms of meiofauna in the deep sea may last until complete disaggregation of the cuttings.