Cape eelgrass

You’re slowly cruising along the Keurbooms River when the boat motor sputters and dies, and once you pull it up out of the water, there clogged in the propeller is a clump of Cape eelgrass or zostera grass Zostera capensis. You’re swimming in the Keurbooms and something slides along your leg and gets tangled around your ankle and with a jerk you find it is only eelgrass. You’re fishing in the Keurbooms and your hook gets stuck, with a yank you pull out a hookful of eelgrass. Cape eelgrass grows in the intertidal zone and has protected meristems, a strong root system and long flexible leaves (10-30 cm long and 1mm wide) which allows it to grow under strong tidal currents, and they are able to tolerate periods of exposure and desiccation. Eelgrass is fast growing but has a variable distribution as large areas can be washed away in floods, and fluctuate in response to bait digging, boat disturbance, and changes in water quality. Cape eelgrass is the dominant seagrass found in South Africa and occurs in 62 sheltered estuaries along 3000km of coastline, from Olifants Estuary on the west coast to Kosi Bay on the east coast. The Keurbooms system has one of the largest areas of Cape eelgrass, as does the Knysna Estuary, but while Knysna has some formal protection status the Keurbooms does not. Despite its wide range, eelgrass is classified as Vulnerable according to IUCN, with a decreasing population. Cape eelgrass is a keystone species, and eelgrass beds form a vitally important habitat, shelter, foraging site, and nursery for a variety of invertebrate and fish species. Eelgrass also provide other ecosystem services such as sediment stabilization, erosion prevention, nutrient recycling, and carbon sequestration. So next time you are boating, swimming, or fishing, appreciate the incredible species we are fortunate enough to have growing in our area!

Written by: Minke Witteveen

For further reading:

• Adams, J.B. 2016. Distribution and status of Zostera capensis in South African estuaries — A review. South African Journal of Botany 107: 63-73.
• Short, F.T., Coles, R., Waycott, M., Bujang, J.S., Fortes, M., Prathep, A., Kamal, A.H.M., Jagtap, T.G., Bandeira, S., Freeman, A., Erftemeijer, P., La Nafie, Y.A., Vergara, S., Calumpong, H.P. & Makm, I. 2010. Zostera capensis. The IUCN Red List of Threatened Species 2010. Accessed: 2016-12-18. URL: http://www.iucnredlist.org/details/173370/0.