Macroinvertebrate assemblages from two sampling methods similarly discriminated freshwater wetlands with different ecosystem status in south Texas

Abstract

Resacas of the lower Rio Grande River (secondary channels, distributaries, oxbow lakes) are vital freshwater wetlands under intense anthropogenic pressure. Many of these wetlands have their water levels tightly managed and some are being restored. Reliable bioassessment methods to effectively discriminate among resacas of differing ecological status are needed. Common components of bioassessments for aquatic ecosystems include surveys of biological communities, among which the macroinvertebrates are generally considered the most accurate. The macroinvertebrate community of resacas is virtually undocumented and various sampling methods have never been used in parallel. Here we used two popular sampling techniques (benthic corer and dip net), while producing the first portrait of the macroinvertebrate community inhabiting resacas. Despite sampling different invertebrate assemblage subsets, both methods discriminated among studied resacas in a similar manner; however, the corer presents several advantages including: 1) a much higher precision (based on coefficients of variation), 2) more adequate representation of an indicator species (invasive gastropod), and 3) clearer differences in functional feeding groups among resacas which constitutes an additional indicator metric.