Pondweed in Zandvlei David Walker
What is pondweed? • Angiosperm (flowering plant) • Indigenous • Has long, ribbon-like leaves, and a rhizome with starch-filled tubers • Also known as sago pondweed or fennel pondweed • Scientific name is now Stuckeniapectinata, but used to be called Potamogetonpectinatus
Where does in grow? • Restricted to shallow water (usually <3m), because of a need for light • Prefers brackish water (5-15 ppt salinity) • Responds positively to nutrients • Grows rapidly (up to 2.5 ha per year) • So Zandvlei is the perfect home!
Role in the ecosystem1 • Dampens wave action • Important food source for red-knobbed coots and fish (especially carp) • Absorbs nutrients • Competes with and limits growth of unicellular algae, so can help to prevent nuisance (potentially toxic) algal blooms, e.g. blue-greens (cyanobacteria) • Clarifies water • Nesting sites for coots
Role in the ecosystem2 • Oxygenates the water when in active growth phase • Provide attachment sites and /or habitat for filamentous algae and invertebrate species • Important as a refuge and food source for indigenous fish species – significant as Zandvlei is only functional estuary of any size within False Bay
Problems • Restricts water flow – therefore lessen scouring effect of floods • Restricts boating • Dies off at end of growing season, and then releases nutrients into water. Can then contribute to toxic algal blooms. • Subsequent stagnation can then lead to oxygen deficiency (and therefore fish kills).
Because of the stresses placed upon the Zandvlei estuary, the pondweed has to be managed artificially……..