Análise da fauna bentônica da plataforma do Rio Doce depois do desastre de Mariana-Mg: expedições de monitoramento 2015 e 2016

Abstract

The Rio Doce flows into the Continental Shelf located on the coast of the State of Espírito Santo. On November 5, 2015, a disaster occurred with the rupture of the tailings dam operated by the Samarco mining company in Mariana, a small city in the Central Region of Minas Gerais State. After the disaster, it was necessary to create a monitoring plan for environmental impact assessment. Since then, several expeditions with oceanographic ships of the Navy and Research Institutions have been carried out, such as the Vital Expedition of Oliveira from November 27 to 29, 2015; Antares Expedition from February 16 to 18, 2016 and the Soloncy Moura Expedition from April 20 to 26, 2016. The main goal was to characterize the benthic fauna and sediment bottom in the Rio Doce continental shelf, during the monitoring of the three sampling expeditions, after the arrival of the tailings from the Samarco dam in the marine environment. In the laboratory, the samples were passed through granulometry screens to separate the macrofauna. The organisms were kept in 10% formaldehyde, sorted, identified to the possible taxonomic levels and quantified using a stereoscopic microscope and optical microscope. The total number of organisms screened in the 45 samples was 5,956; the main groups were: "Gastropoda Class Shell", the Bryozoa Phylum, "Bivalvia Class Valve", Scaphopoda Class and Bivalvia Class. The occurrence of the taxonomic groups was associated to the different granulometric contents that make up the background substrate. The Class Gastropoda has occurrence in the sandy and muddy sediment, and a smaller occurrence in the gravel sediment was also registered; the individuals of the Phylum Bryozoa were associated to the occurrence of sandy sediment and less frequently in the muddy and gravel sediment. The "valve of Class Bivalvia", the Class Scaphopoda and Class Bivalvia occurred in the sandy and muddy sediment, and with low content in the gravel sediment. When comparing the occurrence of organisms in the Vital Expeditions of Oliveira, Antares and Soloncy Moura, it was verified that the highest relative frequencies of the Gastropoda Class were registered in the Soloncy Moura Expedition, five months after the arrival of the mud. Phylum Bryozoa presented the highest frequency in the Antares Expedition, three months after the contamination. The Bivalvia Class valve showed the highest relative frequency in the Soloncy Moura Expedition, 5 months after the disaster. The Scaphopoda Class presented its highest relative frequencies in the Soloncy Moura Expedition five months after the arrival of the sludge. The Bivalvia Class exhibited the highest relative frequency in the samples from the Vital Expedition of Oliveira, twenty-two days after the arrival of the tailings. When comparing the occurrence of organisms from pre-and post-disaster samples, it was observed that most of the samples from the Vital Expedition of Oliveira, Antares and Soloncy Moura had some type of alteration in the communities, with the increase or reduction of some groups, such as for example, the Bivalvia Class valve and the Gastropoda Class, and the disappearance of important groups such as the Subfilo Crustacea, the Polychaeta Class tube. These results contributed to the environment damage evaluation caused by this important marine contamination.