8 Facts about Knysna’s rich eelgrass/seagrass beds
1. The Knysna Estuary is SA’s foremost locality for seagrass, containing more than half the entire country’s seagrass meadow. The dominant species is Cape eelgrass (Nanozostera capensis).
2. Seagrass is not grass, but more closely related to lilies, gingers and arums. They are the only flowering plants that are able to live their whole lives submerged in seawater and even flower under water.
3. Seagrass meadows may appear uniform, monotonous and lacking interest. But they teem with life – small and most hidden from sight.
4. A survey in late summer 2011 along the north shore of Leisure Isle found an average of over 6,200 small animals living at or just below each m2 of surface, and a total of more than 90 species, including 35 types of worm, 25 crustaceans, 12 sea-snails, 6 sea-slugs, and one each of starfish, brittlestars, sea-urchins and sea-cucumbers.
5. Seagrass is globally ranked the third-most valuable natural habitat 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, later to be caught in deeper water and offshore.
6. Illicit pumping for prawns and trenching for worms in the Marine (Bait) Reserve, and lack of policing, is threatening the seagrass – despite the reserve status. Fortunately, as a whole, the Knysna seagrass beds are suffering less than most, but pressure is unlikely to decrease.
7. Walking across seagrass beds is not encouraged as it’s very sensitive to trampling.
8. Marine biology expert, Prof Brian Allanson of the Knysna Basin Project and LI resident, says that currently, the eelgrass is not spreading, and while of concern, the eelgrass meadows’ size and health are cyclical and constantly shifting.
Extracts from an article by Dr Richard Barnes, long-time Cambridge Zoology Dept academic, and also at Rhodes University. See more at the Steenbok Nature Reserve website