Influences of multiple anthropogenic disturbances coupled with a tailings dam rupture on spatiotemporal variation in fish assemblages of a tropical river

Abstract

The Mariana disaster, resulting from the rupture of the Fundão tailings storage facility (TSF) in 2015, was a large-scale environmental disaster that drastically affected the entire channel of the Rio Doce, southeastern Brazil. The disaster produced substantial channel siltation, increased turbidity, riparian damage and a massive fish kill. However, the Rio Doce basin has a long history of environmental degradation, including hydroelectric dams. The latter are major threats to the ichthyofauna because they affect flow regimes, trap sediments and large wood, select generalist species, impair fish migrations and favour non-native invasive species. In this study, we analysed the effects of the rupture as well as impacts from the construction of a run-of-the-river hydroelectric dam on native and non-native fish abundances, and species richness and composition in the middle Rio Doce. To do this, we examined fish survey data collected before and after each disturbance upriver of the reservoir, in the reservoir area and downriver of the dam. The data were separated into three temporal intervals: free-flowing river, post-filling reservoir and post-TSF disaster. To assess temporal changes in native and non-native fish species richness, we used a rarefaction method and tested it with two-way ANOVA, which also was used to compare fish abundances. To test temporal changes in fish assemblage composition we used a PERMANOVA test. We observed no significant differences in total native or non-native species richness as a result of the dam or the disaster. However, we did observe increased non-native individual abundances after the TSF rupture as well as native individual abundances, depending on the location studied. The assemblage composition also changed after dam construction and the TSF rupture, except for the upriver reach after dam construction. We conclude that both the dam and the TSF rupture affected fish assemblages, favouring increased non-native abundances, and also changed fish assemblage composition. Our results suggest that a century of landscape and riverscape pressures had extirpated the sensitive fishes from the Rio Doce before the TSF rupture. We conclude that multiple long-term chronic disturbances can be as harmful to aquatic biota as the acute effects of a major environmental disaster.