SEASONAL WINTER POOLS OF THE HELDERBERG BASIN

By Pat Reavell
preavell@absamail.co.za

In the S.W. Cape there are coastal fresh and brackish lagoons, as well as river systems all with some degree of protection. Small permanent dams have been formed recently by European settlers and contain a restricted aquatic invertebrate fauna, mainly of eurytopic and widely distributed species found elsewhere in cooler parts of South Africa.

However the natural seasonal winter pools , which dry up during the Mediterranean summer, contain many unique Western Cape endemics, mainly invertebrates such as; microcrustacea, water mites, a few water bugs, and many water beetle species endemic to this afromediterranean biome. These seasonal surface waters have lower temperatures than the permanent pools, and are covered by land plants during the dry season.

During the rainy season inundated vegetation triggers a microbial food base for a rapid succession of aquatic invertebrates many confined to these pools. The predatory backswimmer Notonecta lactitans and predatory diving beetles; Rhantus circurius, Hydropeplus trimaculatus, Primospes suturalis, Darwinhydrus solidus, Copelatus platynotus, and Andex insignis are characteristic . The lesser known water scavenger beetles or hydrophilidae contain even more species than the aforementioned Dytiscidae, and may contain many endemic species.

A range of flowering plants are confined to these pools, including the culturally important water hawthorn or waterblometjie. During the dry summer these plants either die back to underground storage organs, or become terrestrial.

A few frogs such as the cape river frog and clicking stream frog breed here and form food for various water birds.

From this brief report it should be clear that the protection of these pools is important. The major problem with permanent man made dams is that they contain predatory and disruptive alien fish such as bass, carp, and Mozambique kurper. Apart from changing the water clarity, the two bass species are voracious predators on most invertebrates. In the Helderberg Basin, there are some winter pools in Victoria flats an area which may be zoned for housing. Also AECI Heartlands property, and Lourens river floodplain have a few excellent winter pools. Sadly due to rapid housing expansion, many of the remaining pools are being lost thus a protection policy should be implemented for the remaining pools and ditches.