Assessing the extent, effects, and management strategies for aquatic invasive alien species in protected areas in Mpumalanga, South Africa.

Abstract

Aquatic invasive species pose a significant threat to biodiversity and ecosystem functioning, including in protected areas meant to preserve native and often endemic species. However, despite growing awareness of their ecological and economic impacts, the management of aquatic invasive species is still not fully integrated or consistently prioritised within broader conservation strategies. The study aimed to assess the presence of aquatic invasive species, their occurrence, and their effects on non–native species, as well as evaluate the effectiveness of current management strategies for aquatic invasive species within the protected areas of the Mpumalanga Province, South Africa. This body of work represents fieldwork, laboratory experiments, and social components undertaken from May 2023 to June 2025. Only one invasive species, Xiphophorus helleri (Swordtail), was recorded, and it occurred exclusively at the SANBI–Lowveld National Botanical Garden. In that protected area, X. helleri was also the most abundant species, while it was absent from the other five protected areas. The study further revealed that X. helleri exhibited rapid growth and competitive superiority, which contributed to its ability to outcompete native species, including Micralestes acutidens (sharptooth tetra), Pseudocrenilabrus philander (mouthbrooder), Oreochromis mossambicus (mozambique tilapia), and Enteromius eutaenia (orangefin barb). Mortality rates were found to be low, suggesting that there were few negative factors affecting the X. helleri population in the SANBI Lowveld National Botanical Garden. Moreover, the study examined the feeding interactions between the native mouthbrooder (P. philander) and the non–native swordtail (X. helleri) when offered a readily consumed prey item (Chironomidae). The results revealed that predator–predator interactions were primarily additive, with minimal non–trophic effects observed, suggesting that swordtail invasion could increase pressure on prey communities if total predator abundances concomitantly increased. Furthermore, the results revealed significant gaps in aquatic invasive species management, including the absence of species checklists, inconsistent monitoring, limited formal training, and inadequate funding. While some participants drawn from semi–structured interviews with workers responsible for invasive species management in protected areas reported collaborative efforts and the use of adaptive strategies, many reserves lacked baseline data and clear decision–making frameworks. The findings suggest that although awareness of aquatic invasive species threats exists, practical implementation of management strategies remains limited and fragmented. Constraints such as inadequate funding and insufficient targeted training impede the effective implementation of aquatic invasive species management strategies. Strengthening aquatic invasive species management in Mpumalanga’s protected areas requires long–term funding, targeted training, improved documentation of invasive species data and management strategies, and inter–agency collaboration.