Transcript 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 Stuckenia pectinata, but used
to be called Potamogeton pectinatus
Where does in grow?
 Restricted to shallow water (usually <3m), because of a
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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
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(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……..