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……..