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 Stuckenia pectinata, but used to be called Potamogeton pectinatus

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……..