Invasive alien aquatic plants (IAAPs) have severe ecological and socio-economic impacts on freshwater systems in southern Africa and beyond. The application of biological controls against floating IAAPs has significantly improved freshwater ecological and socio-economic returns, but the overall effects of successful biological control on ecosystem recovery remains poorly understood. This study quantifies ecosystem recovery and long-term ecological effects following mechanical and biological control of Salvinia molesta. A combination of mesocosm (Before/After, Control/Impact) and field (Before/After) experiments were employed to test: (i) changes in water quality, (ii) shifts in phytoplankton, periphyton and aquatic macroinvertebrate assemblages, and (iii) shifts in trophic dynamics and aquatic food web structure before and after S. molesta management. Mechanical removal and biological control of S. molesta did bring about ecological recovery and ecosystem re-organisation, however, mechanical removal proved unsustainable by allowing a coinciding linear regime-shift from clear water to a submerged (Ceratophyllum demersum) and later, emergent (Nymphaea nouchali) IAAPs dominant state. This presentation will discuss ecological changes before and after S. molesta management using both mesocosm and field evidence and highlight possible restoration implications of the control methods for floating IAAPs. In conclusion, a biological control programme for IAAPs management, followed by active restoration practices (introduction of native macrophytes) is recommended. This study provides support for informed management recommendations for ecosystem recovery and restoration of invaded aquatic ecosystems in southern Africa and worldwide.
Audio/Video, Conference Presentation, SER2019
Society for Ecological Restoration