The rainy season increases the abundance and richness of the aquatic insect community in a Neotropical reservoir.

Hs Santana,Cl Pereira,R Angelini,J Simião-Ferreira,Lcf Silva

doi:10.1590/1519-6984.09213

Abstract

Alterations in aquatic systems and changes in water levels, whether due to rains or dam-mediated control can cause changes in community structure, forcing the community to readjust to the new environment. This study tested the hypothesis that there is an increase in the richness and abundance of aquatic insects during the rainy season in the Serra da Mesa Reservoir, with the premise that increasing the reservoir level provides greater external material input and habitat diversity, and, therefore, conditions that promote colonization by more species. We used the paired t test to test the differences in richness, beta diversity, and abundance, and a Non-metric Multidimensional Scaling (NMDS) was performed to identify patterns in the community under study. Additionally, Pearson correlations were analyzed between the richness, abundance, and beta diversity and the level of the reservoir. We collected 35,028 aquatic insect larvae (9,513 in dry period and 25,515 in the rainy season), predominantly of the Chironomidae family, followed by orders Ephemeroptera, Trichoptera, and Odonata. Among the 33 families collected, only 12 occurred in the dry season, while all occurred in the rainy season. These families are common in lentic environments, and the dominance of Chironomidae was associated with its fast colonization, their behavior of living at high densities and the great tolerance to low levels of oxygen in the environment. The hypothesis was confirmed, as the richness, beta diversity, and abundance were positively affected by the increase in water levels due to the rainy season, which most likely led to greater external material input, greater heterogeneity of habitat, and better conditions for colonization by several families.

Highlights

Aquatic communities are highly impacted due to the damming of the rivers for power generation (Barletta et al, 2010), causing the homogenization of environments, introduction and permanence of exotic species, extinction of local species, loss of habitat, and interruption of fish migration (Agostinho et al, 1999, 2008)
The Serra da Mesa Reservoir is located in the north of Goiás State, near the border with the state of Tocantins (Figure 1), and is the main drainage basin of the Tocantins River and four tributaries: the Tocantinzinho, Bagagem, Almas, and Maranhão rivers (Andrade, 2002)
Among the 33 families collected, only 12 occurred in the dry season, while all occurred in the rainy season

Summary

Introduction

Aquatic communities are highly impacted due to the damming of the rivers for power generation (Barletta et al, 2010), causing the homogenization of environments, introduction and permanence of exotic species, extinction of local species, loss of habitat, and interruption of fish migration (Agostinho et al, 1999, 2008). The water level variations caused by reservoir operations (Pamplin and Rocha, 2007) alter the richness and density of many organisms and interfere with such parameters as the water transparency and input of organic matter (Hunt and Jones, 1972; Palomaki, 1994; Furey et al, 2006). In the tropics, where this variable does not have large variations, other variables are crucial, including physical-chemical parameters of the water, seasonality, and habitat heterogeneity (Bispo and Oliveira, 1998; Silveira et al, 2006)

Methods

Results

Conclusion