Pondweed in Zandvlei
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Transcript of Pondweed in Zandvlei
Pondweed in ZandvleiDavid Walker
What is pondweed?Angiosperm (flowering plant)IndigenousHas long, ribbon-like leaves, and a rhizome
with starch-filled tubersAlso known as sago pondweed or fennel
pondweedScientific 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 lightPrefers brackish water (5-15 ppt salinity)Responds positively to nutrientsGrows rapidly (up to 2.5 ha per year)So Zandvlei is the perfect home!
Role in the ecosystem1Dampens wave actionImportant food source for red-knobbed coots
and fish (especially carp)Absorbs nutrientsCompetes with and limits growth of
unicellular algae, so can help to prevent nuisance (potentially toxic) algal blooms, e.g. blue-greens (cyanobacteria)
Clarifies waterNesting sites for coots
Role in the ecosystem2Oxygenates the water when in active growth
phaseProvide attachment sites and /or habitat for
filamentous algae and invertebrate speciesImportant as a refuge and food source for
indigenous fish species – significant as Zandvlei is only functional estuary of any size within False Bay
ProblemsRestricts water flow – therefore lessen
scouring effect of floodsRestricts boatingDies 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……..