Aim and scope of the project: A mesocosm experiment is an outdoor experimental system that examines the natural environment under controlled conditions. These systems are used to investigate the behaviour of fishes that are difficult to observe under natural conditions or they are used to determine the impact invasive species have on native ecosystems. The anthropogenic spread of invasive species is becoming a global problem and the potential for invasive species to alter ecosystems are high. Research has demonstrated that biological invasions have an impact on ecosystem functioning and biodiversity. Unfortunately, there are still large gaps in the current spread and impacts of invasive species. This study aims to use mesocosms to evaluate what effect native fish (Coptodon rendalli) have on aquatic invertebrates, what effect the invasive red claw crayfish (Cherax quadricarinatus) have on the native ecosystem, and what effect invasive predators like bass (Micropterus salmoides) and/or native predators like eels (Anguillids) have on the invasive red claw crayfish.


Client and/or collaborating stakeholders: University of Mpumalanga


Interesting and important outcomes/prospects: The Australian red claw crayfish, Cherax quadricarinatus, native to Australia and Papua New Guinea was first reported in South Africa in 2002, after accidentally escaping from an aquaculture farm in Swaziland. The species is now present in at least four large rivers (Komati, Crocodile, Mbuluzi and Usutu), two tributaries (Lomati and Mlawula rivers), several irrigation dams in Mpumalanga Province as well as the Van Graan Dam at the border of the Kruger National Park (KNP). While the environmental impact of the red claw crayfish in invaded habitats has yet to be determined, it has potential impacts on native biotas, such as disease introductions or strong competitive interactions with native freshwater crustaceans. A better understanding of the red claw crayfish distribution, habitat preferences, rate of spread and impacts on the local aquatic ecosystems is urgently required to develop mitigation strategies that minimise the spread of this invasive crayfish in the KNP and the Komati Catchment. This mesocosm experiment will give us a better understanding of the effect of the red claw crayfish on local aquatic ecosystems.

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