Macroinvertebrados bentônicos e a estrutura do habitat em um rio intermitente do semiárido brasileiro

Abstract

Benthic invertebrates and the habitat structure in an intermittent river of the semi-arid region of BrazilMacroinvertebrados bentônicos e a estrutura do habitat em um rio intermitente do semiárido brasileiro AbstractInteractions between the habitat structure and physical and chemical parameters generate environmental conditions that influence the distribution and abundance of macroinvertebrate species and their assemblages. This study describes the habitat structure and its effects on macroinvertebrate composition in an intermittent stream in the Brazilian semi-arid. Collections of benthic invertebrates were performed in three reaches along the Ipanema River during the dry and wet seasons using a "D" shaped net (40 cm wide and 250 μm mesh). A total of 23 taxa was recorded, Insecta being the most representative with 12 families and an average density of 168.1 ind/m². Correlations between environmental variables and CCA axes showed that substrate composition (sand and mud), macrophytes, litter and altitude were the main variables explaining benthic macroinvertebrate composition in the study stream. Canonical correlations between macroinvertebrate and physical and chemical variables were not significant. This study shows that the habitat structure contributes to the persistence and stability of macroinvertebrate communities in a Brazilian semi-arid stream, by creating refugia for organisms and contributing to the physical structures available for colonization.

First record of Lopescladius Oliveira, 1967 (Chironomidae: Orthocladiinae) in the Piranhas-Açu River basin, Brazil, with ecological notes on its habitat use

“…Overall, underwater structures usually abundant in Brazilian semi-arid intermittent streams, such as littoral grass, woody debris, and macrophytes (Medeiros et al 2008;Carvalho et al 2013), were either not present or present in low proportions during the sampling for the present study. Furthermore, dissolved oxygen concentration and conductivity were low, compared to other sites in intermittent streams, whereas transparency was high (e.g., Farias et al 2012;Carvalho et al 2013). Temperatures typically do not fluctuate greatly in Brazilian semi-arid streams (Farias et al 2012).…”

“…Even though identification to the level of species is desirable in taxonomic studies, we highlight that many orders of insects will occur in aquatic systems only during their larval, pupae or nymph stages and it is not possible to have the information of first occurrences in advance to allow the capture of live individuals for posterior identification of the adult stages. Studies for intermittent streams of Brazil, often report large numbers of Chironomidae (Farias et al 2012;Rocha et al 2012;Carvalho et al 2013), with average densities reaching thousands of individuals per square meter (refer to the studies cited above for information on sampling effort and design). This makes Lopescladius an inconspicuous taxon in intermittent streams of Brazil, occurring in low densities, which is corroborated by the few studies that cite this genera to northeastern Brazil (Freitas 2004;Soares et al 2013).…”

“…Taxa of the Harnischia complex and Lopescladius are known for inhabiting sandy lotic environments (Sanseverino and Nessimian 2001), such as in the present study. However, the presence of rocks, gravel, and cobbles and deeper areas must be noted and is likely to enhance the spatial segregation of the genus to sandy patches, contributing to the overall spatial segregation in Chironomidae reported for Brazilian intermittent streams (Farias et al 2012;Carvalho et al 2013). Overall, underwater structures usually abundant in Brazilian semi-arid intermittent streams, such as littoral grass, woody debris, and macrophytes (Medeiros et al 2008;Carvalho et al 2013), were either not present or present in low proportions during the sampling for the present study.…”

“…However, the presence of rocks, gravel, and cobbles and deeper areas must be noted and is likely to enhance the spatial segregation of the genus to sandy patches, contributing to the overall spatial segregation in Chironomidae reported for Brazilian intermittent streams (Farias et al 2012;Carvalho et al 2013). Overall, underwater structures usually abundant in Brazilian semi-arid intermittent streams, such as littoral grass, woody debris, and macrophytes (Medeiros et al 2008;Carvalho et al 2013), were either not present or present in low proportions during the sampling for the present study. Furthermore, dissolved oxygen concentration and conductivity were low, compared to other sites in intermittent streams, whereas transparency was high (e.g., Farias et al 2012;Carvalho et al 2013).…”