Biodiversity assessment of benthic macroinvertebrates along a reservoir cascade in the lower São Francisco river (northeastern Brazil)

Abstract

In order to verify the cascade-system effect in benthic macroinvertebrate communities, and the implications for policy making and proposals for conservation and sustainable use of the lower portion of São Francisco river basin (Bahia State, Brazil), a three-reservoir cascade system including two stretches downstream were studied during dry (June, 1997) and rainy (March, 1998) periods. The dominant groups found were Mollusca (Melanoides tuberculata), Oligochaeta, and Chironomidae larvae. Low Shannon-Wiener and Pielou index values were found, but with no significant difference between the sampling periods. However, density and taxonomic richness were significantly different (t (0.05; 31) = -2.1945; p < 0.05; e t (0.05; 31) = -3.0600; p < 0.01) between the sampling periods, with a reduction in the number of taxa and macroinvertebrate abundance during the rainy period. An increasing gradient in benthic macroinvertebrate community structures was noted along the reservoir cascade from the first reservoir (Apolônio Sales), followed by a decrease downstream from the third reservoir of the system (Xingó). Despite the negative consequences of rapid proliferation of dams, which have caused widespread loss of freshwater habitats, the reservoir cascade system promoted an increase in benthic macroinvertebrate diversity, due to water-quality improvement along the system. Key words: benthic macroinvertebrates, reservoir, biodiversity assessment, reservoir cascade concept, São Francisco river. RESUMO Avaliação da biodiversidade de macroinvertebrados bentônicos ao longo de uma cascata de reservatórios no baixo rio São Francisco (nordeste do Brasil)Com o objetivo de determinar o efeito da cascata de reservatórios nas comunidades de macroinvertebrados bentônicos e sua possível implicação para a definição de políticas e propostas para conservação e uso sustentável da porção baixa da bacia do rio São Francisco (Bahia, Brasil), amostragens foram realizadas em três reservatórios e dois trechos a jusante do último reservatório, durante os períodos de seca (junho de 1997) e chuvas (março de 1998

Diversity and distribution of mollusks along the Contas River in a tropical semiarid region (Caatinga), Northeastern Brazil

“…Thus, the use of an inappropriate sampler to collect mollusks seems to not have affected knowledge of the diversity of the Contas River malacofauna. The results obtained in this study also concord with the findings of the few available studies on the macroinvertebrate communities of semiarid rivers in the Brazilian Northeast region, in which insects are the most diversified and abundant group, but mollusks are also frequent, with some dominant taxa such as the invasive M. tuberculata (Maltchik 1999, Callisto et al 2005, Andrade et al 2008, Santana et al 2009). On the other hand, it should be expected that mollusk richness in tropical semiarid regions, where the dry period is prolonged and creates adverse conditions for the freshwater malacofauna, will be smaller than the mollusk richness in regions with more permanent waterbodies.…”

Using oligochaeta assemblages as an indicator of environmental changes

“…Therefore, the construction of dams can cause profound negative effects on aquatic biodiversity because the natural seasonal patterns to which the fauna has adaptations is altered, and normal seasonal migration paths (drifts) are blocked (Rosenberg et al 2000). Callisto et al (2005) observed that reservoirs in cascades cause significant changes in the original continuum of a river, altering the thermal heterogeneity, the connectivity, the fine and the coarse particulate organic matter rates. These changes can lead to significance effects on the communities of invertebrates, causing loss of aquatic diversity.…”

“…Moreover, it causes loss of habitats and diversity due to geomorphologic adjustment of the river system toward a new equilibrium condition (Petts and Greenwood, 1985). These impacts are increased when dams are built in series (Barbosa et al, 1999;Callisto et al 2005).…”

“…Benthic macroinvertebrates are one of the groups affected by the cascade of reservoirs (Callisto et al, 2005;Jorcin and Nogueira, 2008). The flow regulation and stratification patterns developed in reservoirs frequently impact the biota downstream in four ways (Cortes et al 2002): i) alteration of physical and chemical characteristics associated with the release of water and sediment derived from the hypolimnion, that affect life history and density of macroinvertebrates (Cortes et al 2002); ii) alteration of available food resources to aquatic biota, specially through changes in the particulate organic matter (McAllister et al 2001); iii) creation of unstable environment due to daily changes in water level, increasing invertebrate drift (Hansen and Closs 2007); and iv) reduction of water released downstream, which modify abundance and diversity of benthic fauna (Bunn and Arthington, 2002).…”

The introduced snail Melanoides Tuberculatus (Muller, 1774) (Mollusca: Thiaridae) in aquatic ecosystems of the Brazilian Semiarid Northeast (Piranhas-Assu River basin, State of Rio Grande do Norte)

“…The gastropod M. tuberculatus shows great adaptability to different ecological conditions, but its successful establishment is frequently associated with eutrophic environments (Martins- Silva and Barros, 2001;Callisto et al, 2005;Giovanelli et al, 2005;Vidigal et al, 2005;Rocha-Miranda and Martins-Silva, 2006). Areas located near the Rio Doce State Park in the state of Minas Gerais, which are impacted by eucalyptus plantations, were also favourable for the development of high densities of this species (Vidigal et al, 2005).…”