Turnover of benthic macroinvertebrates along the Mthatha River, Eastern Cape, South Africa: implications for water quality bio-monitoring using indicator species

Abstract

ABSTRACTThe ecological integrity of the Mthatha River is increasingly under threat from climate change and anthropogenic impacts of contamination by acidification, organic pollutants, industrial and agricultural chemicals, and waste water. This study assessed the ecological state of the river and the impact of water quality on benthic macroinvertebrate communities from 2015 to 2016. Faunal specimens were sampled and environmental variables measured at four sites that vary in topography and human impact along the river. A total of 2980 specimens were recorded at sites, and classified into 12 orders, 46 families and 71 species. Species composition and distribution were directly or indirectly affected by season, physico-chemical variables and habitat heterogeneity. CCA results showed that electrical conductivity, pH, temperature, dissolved oxygen and vegetation accounted for species distribution patterns. Both habitat-restricted and common/widespread species can be used as indicators for assessing the quality of the Mthatha River system. Habitat management along the river should aim at preserving sufficient indigenous vegetation, especially during summer when biotope requirements are optimal. The practicality of using species-level surveys on a routine basis can be challenging. It might be advisable to select a few indicator species identified in this study and to monitor them as surrogates for the whole community.