Abstract
Urbanisation in South Africa has resulted in the degradation of aquatic ecosystems across a rural-to-urban gradient; impacting the availability of clean water. Biological organisms, including fish assemblages, have been used as indicators of environmental change, as part of monitoring programmes designed to protect and improve aquatic ecosystem conditions. However, the effectiveness of individual freshwater fish species as bio-indicators for urban impacts has not yet been evaluated. This study investigated the occurrence of freshwater fish species across three urban gradients within the upper Crocodile River sub-management area as potential bio-indicators. Having collected presence and absence data, five native fish species were determined to be widespread. Their effectiveness as bio-indicators for six environmental drivers, identified through principle component analysis, was assessed using species stressor-response curves derived from logistic regression analysis. Of the five species, the largescale yellowfish (Labeobarbus marequensis) and stargazer catfish (Amphilius uranoscopus) showed potential to be effective bio-indicators for urban impacts on aquatic water quality and instream habitat. These taxa, as effective urban bio-indicators, have the potential to improve the efficiency of urban river health assessments through reducing data gathering and staff training requirements.
Highlights
South Africa’s aquatic ecosystems provide numerous essential ecosystem services, including the provision of water to rural communities, and ensuring water and food security, supporting socio-economic development (Karr and Chu, 2000; Ollis et al, 2006)
Fish have become well established in South Africa as an assemblage-level indicator of ecosystem health, and in this study confirmed that rivers decline in their eco-status classification across a rural-to-urban gradient
Two widespread fish species within the upper Crocodile River sub-management area were identified as potential species-level bio-indicators of stressors associated with urbanisation
Summary
South Africa’s aquatic ecosystems provide numerous essential ecosystem services, including the provision of water to rural communities, and ensuring water and food security, supporting socio-economic development (Karr and Chu, 2000; Ollis et al, 2006). Urban impacts on freshwater ecosystems include alteration of instream habitats through canalisation, sedimentation and the loss of riparian vegetation (Paul and Meyer, 2001) and physico-chemical change through polluted runoff and the inflow of sewage from wastewater treatment works (Nyenje et al, 2010). These physical and chemical alterations can have severe impacts on aquatic biodiversity, ecological function, and the usability of the water as a resource to human communities downstream (Paul and Meyer, 2001; Jackson et al, 2016). Fish, being relatively long-lived and occurring at various trophic levels (Armon and Hänninen, 2015), are frequently used as bio-indicators, as they can respond to a multitude of physical, chemical and biological processes within the aquatic environment, across wide temporal scales (Kleynhans, 1999)
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