Fate of seagrass beds uncertain
Knysna does not only, as the advertising slogans tell the visitor, boast South Africa’s favourite estuary, but is also South Africa’s most important locality for seagrass, since this area contains more than half of the entire country’s seagrass meadows.
The shores around Leisure Isle, particularly those adjacent to Steenbok Nature Reserve and Kingfisher Creek, contain some of the best stands of seagrass in Knysna.
What is seagrass and why is it important?
Seagrass is not a type of grass, but rather flowering plants, usually with grass-like leaves, that are able to live their whole lives submerged in seawater. Seagrass meadows, like coral reefs, are centres of great biodiversity, highly productive and currently disappearing from the planet at an alarmingly fast rate. To date it is only the fate of the visually beautiful coral reefs that has stirred the public imagination.
The Knysna seagrass beds teem with a wide variety of life, but many of the life forms are small and most are hidden from sight. Earlier this year a survey along the northern shore of Leisure Isle by the eminent marine biologist, Dr Richard Barnes, revealed an average of over 6,200 small animals living at, or just below, each square metre of surface. These included crustaceans, sea-snails, worms, sea-slugs, sea-cucumbers and many other creatures.
Some of these animals are of national or international significance. For example, Knysna is the only place in the whole of Africa where a certain sea-slug and a type of sea-snail are known to occur. Two other animals (the seagrass false-limpet and the dwarf cushion-star), found only in Knysna and at Langebaan on the West Coast, are threatened at their West Coast site because of the loss of their seagrass habitat. This begs the question of how much longer they will be safe here.
Seagrass is globally ranked as the third most valuable natural resource per unit area to humans. Seagrass beds filter nutrient and various chemical inputs out of the water, stabilise sediments and, most importantly, provide a nursery area for commercially-important species of prawns and fish, which can later be caught in deeper water and offshore.
Their fate hangs in the balance
Although the beds along the northern shore of Leisure Isle lie within the bait reserve declared by the SA National Parks Board, there are very clear signs of illicit pumping for mud-prawns and trenching for worms. Such extensive bait collecting could eventually destroy the seagrass, which is very sensitive to trampling and trenching in particular. Bait reserves are important to ensure that there will be food for future generations. However, while it is simple to declare areas to be reserves, enforcement is a completely different matter.
Often infringements are a matter of subsistence rather than leisure activity. Also, most bait collectors in Knysna do not believe that their activities are harming the environment. It is clear that urgent new measures will be required to ensure a safe future for South Africa’s premier seagrass site.
Source: The Knysna-Plett Herald