Impacts of mining pollution on coastal ecosystems: is fish body condition a reliable indicator?

Identifying reliable biological indicators is fundamental to efficiently assess human impacts on biodiversity and to monitor the outcomes of management actions. This study investigates whether body condition is an appropriate indicator of putative effects from iron ore mining tailings on marine fishes, focusing on the world's largest mining disaster - known as the Mariana disaster, in Brazil. Eight species were used to test the hypothesis that individuals inhabiting an area severely impacted by tailings have reduced body condition in comparison to those in control areas near (<60 km) and distant (>120 km) from the impact site. Contrary to our prediction, no significant difference in condition was detected between the impacted area and both near and distant controls in seven of the eight species. The results indicate that body condition, as measured by the scaled mass index, has limited applicability as indicator of impact from mining pollution on the fishes analysed. Hypotheses that could explain our findings are proposed, including nutrient provisioning from continental drainage that could indirectly influence fish condition and compensate for the deleterious effects of mining pollution.

Marine fish assemblages of Eastern Brazil: An update after the world's largest mining disaster and suggestions of functional groups for biomonitoring long-lasting effects.

When the Fundão dam collapsed in Brazil, 50 million m3 of iron ore tailings were released into the Doce river, resulting in the world's largest mining disaster. The contaminated mud was transported 668 km downstream of the Doce river and reached the Atlantic Ocean 17 days after the collapse. Seven months later, there was evidence that the tailings had reached the largest and richest coral reef formation in the South Atlantic Ocean. This study provides the first description of species composition, abundance, and diversity patterns of fish assemblages in estuaries, coastal areas, and coral reefs affected by the rupture of the mining dam in the Doce river. A linear mixed model (GLMM) was used to evaluate the influence of salinity on fish abundance across estuarine and coastal ecosystems. In addition, based on functional traits related to habitat use and feeding habits, this study identified fish species suitable as bioindicators of the long-lasting effects of this major mining disaster. Bottom trawls were used to sample five estuaries and their respective coastal areas, and a visual census was employed to sample five reef areas, representing an impact gradient. A total of 269 species were recorded in all three habitats, but only seven were shared among them. The results showed lower similarity in assemblages among estuarine areas compared to the coastal and reef areas. Species composition among estuaries and reef ecosystems was more heterogeneous. In contrast, coastal habitats exhibited high homogeneity. Salinity had no statistically significant effect on fish abundance either in estuaries (p = 0.22) and along the coast (p = 0.14). Twelve fish species were identified as suitable bioindicators for evaluating the long-lasting effects of resuspension of contaminated sediments. These species are commonly found in the ecosystems under the influence of the disaster inhabiting potentially contaminated substrates and substrate-associated benthic preys.

Fish otolith microchemistry as a biomarker of the world's largest mining disaster.

The Fundão dam collapse occurred in late 2015, resulting in the largest disaster in the world involving mine tailings, releasing at least 50 million m3 of iron ore tailings into the Doce river basin (Brazil). Studies realized along the Doce river after the disaster showed high concentrations of some elements above recommended Brazilian standards in different environmental matrices such as Al, Ba, Co, Fe, Hg, Mn, and Ni. This study aims to test the hypothesis that otolith microchemistry can be used as a pollution biomarker over time, that is, the otoliths sampled in the directly impacted area (Doce estuary) will present higher concentrations of the chemical elements in relation to the two other indirectly impacted estuaries (Ipiranga and São Mateus). The marine catfish Genidens genidens was chosen as a sentinel species, as this species presents several features that characterize it as a key species of the estuarine environment. The hypothesis was tested from a comparison between estuaries of the element/Ca ratios (Ba, Fe, and Mn) from the otolith edge (representing more recent deposition) and through the elemental composition profile, from core to edge of otolith. For the otolith edge analyses, it was possible to determine significant differences between estuaries in all three element:Ca ratios (Ba, Fe, and Mn). For the profile analysis (from core to edge), the Doce river showed consistent concentrations of Fe:Ca and Ba:Ca ratios higher than those of the Ipiranga and São Mateus estuaries throughout the life of the fish. In otoliths sampled in the Doce estuary, the possible identified peak of the Ba:Ca and Mn:Ca ratios, was probably associated with the Fundão Dam disaster. The present study showed that otolith microchemistry can be used as a sclerochronological biomarker of metallic aquatic pollution.