The contribution of biocontrol of aquatic weeds to water and biodiversity

The contribution of biocontrol of aquatic weeds to water and biodiversity
Martin P. Hill1 and Julie A. Coetzee2
1Biological Control Research Group, Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown, 6140, South Africa
2Biological Control Research Group, Department of Botany, Rhodes University, P.O. Box 94, Grahamstown, 6140, South Africa

Aquatic ecosystems in South Africa are prone to invasion by several invasive alien aquatic weeds, most notably, Eichhornia crassipes (water hyacinth); Pistia stratiotes (water lettuce); Salvinia molesta (salvinia); Myriophyllum aquaticum (parrot’s feather), and Azolla filiculoides (red water fern). Despite their long history in South Africa, there are only a few studies on the impacts of these species on biodiversity and water loss, while the benefits of the biological control programme against these species has been poorly quantified.  We have used two case studies to show that water hyacinth in particular results in significant water loss, and another two case studies that show its negative impacts on aquatic biodiversity in the field. Further, in controlled large pool experiments, aquatic biodiversity was shown to recover relatively quickly (within one year) after the introduction of biological control on water lettuce. These studies provide justification for the control of invasive alien aquatic weeds in South Africa.  Thus, the long-term management of alien aquatic vegetation relies on the correct implementation of biological control for those species already in the country, and the prevention of other species entering South Africa.