| Scientific Name | Zostera capensis Setch. | Higher Classification | Monocotyledons | Family | ZOSTERACEAE | Synonyms | Nanozostera capensis (Setch.) Toml. & Posl. | Common Names | Eelgrass (e), Seagrass (e), Seegras (a) |
National Status | Status and Criteria | Endangered* B2b(ii,iii,iv,v)c(ii,iv) | Assessment Date | 2018/12/06 | Assessor(s) | J. Adams & D. van der Colff | Justification | This species is widespread across the South African coast and occurs in 62 estuaries. However, it has a very small area of occupancy (AOO) of between 15-18 km². It has been extirpated from two estuaries due to development and human disturbance (Durban Bay and St Lucia) and experiences continuous decline in habitat condition in response to pressures such as eutrophication and dredging. The species also experiences extreme population fluctuations due to natural environmental changes as well as human induced pressures. The species qualifies as Endangered B2b(ii,iii,iv,v)c(ii,iv). Since this is a regional assessment at the national level, a regional adjustment was considered, however, the species is globally assessed as threatened (Vulnerable) and is experiencing continuous decline in many parts of its range, a regional adjustment is therefore not applied, and the species is assessed as Endangered B 2b(ii,iii,iv,v)c(ii,iv) in South Africa. Improved protection is required for the nationally important eelgrass species particularly in the Knysna Estuary, with the greatest area of the species (4.47 km²). |
Distribution | Endemism | Not endemic to South Africa | Provincial distribution | Eastern Cape, KwaZulu-Natal, Western Cape | Range | It occurs from the Olifants Estuary to Kosi Bay. It also occurs in Kenya, Madagascar, Mozambique and Tanzania. |
Habitat and Ecology | Major system | Freshwater | Major habitats | Microestuary, Estuarine Functional Zone | Description | This species occurs in the intertidal zone of permanently open estuaries in South Africa but can be found in temporarily closed estuaries when conditions are saline. |
Threats | | Zostera capensis is extinct in two estuaries in South Africa, the Durban Bay system as a result of habitat loss due to harbour development, reclamation and dredging and in the St Lucia system due to prolonged drought and closed mouth conditions. It has also been lost from a number of small KwaZulu-Natal estuaries due to coastal development, freshwater abstraction and catchment disturbance which has led to an increase in turbidity, sedimentation, mouth closure and loss of intertidal habitat.
Human disturbance as a result of bait digging and disturbance by boats reduces cover and biomass. Eutrophication that causes habitat degradation is a growing threat in South Africa's estuaries as it results in increased algal growth which shades out and outcompetes the species. |
Population | The species experiences extreme fluctuations in population size due to dynamic changes in cover abundance in response to floods, droughts, sedimentation and freshwater abstraction (Talbot et al., 1987; Talbot et al., 1990; Adams and Talbot, 1992; Cyrus et al., 2008; Pillay et al., 2010; Adams, 2016). The number of known subpopulations have been reduced, as two subpopulations have been lost from Durban Bay and the St Lucia system. The subpopulation in the uMhlathuze system is variable due to partial protection by Ezemvelo KwaZulu-Natal Wildlife, and the threat of increased turbidity and silt smothering from dredging. It is a concern that the next largest eelgrass subpopulation occurs approximately 850 km south of uMhlathuze at the Keiskamma Estuary, making recolonization difficult, if a subpopulation is lost, however propagules could still come from the Kosi system. Of the 62 subpopulations of eelgrass, there are only thirteen large subpopulations (Kosi, uMhlathuze, Qora, Keiskamma, Kariega, Bushmans, Swartkops, Kromme, Keurbooms, Knysna, Langebaan, Berg and Olifants) and these have shown varying changes in extent over time, with increases and decreases caused by similar activities such as disturbance from boats, bait digging and trampling. Further investigation is necessary to understand the dynamic responses of this species to environmental changes and habitat disturbance, to improve predictions of future distribution and status (Adams, 2016).
| Population trend | Fluctuating |
Assessment History |
Taxon assessed |
Status and Criteria |
Citation/Red List version | | Zostera capensis Setch. | Least Concern | Raimondo et al. (2009) | |
Bibliography | Adams, J. 2016. Distribution and status of Zostera capensis in South African estuaries—A review. South African Journal of Botany 107:63-73.
Adams, J. and Talbot, M. 1992. The influence of river impoundment on the estuarine seagrass Zostera capensis Setchell. Botanica Marina 35(1):69-75.
Cook, C.D.K. 2004. Aquatic and wetland plants of southern Africa. Backhuys Publishers, Leiden, The Netherlands.
Cyrus, D., MacKay, C. and Weerts, S. 2008. Intrusion of beach-disposed dredger spoil into the Mhlathuze Estuary, South Africa, and its impact on Zostera capensis. African Journal of Aquatic Science 33(3):223-231.
Goldblatt, P. and Manning, J.C. 2000. Cape Plants: A conspectus of the Cape Flora of South Africa. Strelitzia 9. National Botanical Institute, Cape Town.
Manning, J.C. and Goldblatt, P. 2012. Plants of the Greater Cape Floristic Region 1: The Core Cape Flora. Strelitzia 29. South African National Biodiversity Institute, Pretoria.
Pillay, D., Branch, G.M., Griffiths, C.L., Williams, C. and Prinsloo, A. 2010. Ecosystem change in a South African marine reserve (1960–2009): role of seagrass loss and anthropogenic disturbance. Marine Ecology Progress Series 415:35-48.
Raimondo, D., von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. and Manyama, P.A. 2009. Red List of South African Plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
Sieben, E.J.J. 2009. The status and distribution of vascular plants (Magnoliophyta, Lycophyta, Pteridophyta). In: W.R.T. Darwall, K.G. Smith, D. Tweddle and P. Skelton (eds.), The status and distribution of freshwater biodiversity in southern Africa (pp. 83-98), IUCN and SAIAB, Gland, Switzerland and Grahamstown, South Africa.
Talbot, M., Knoop, W. and Bate, G. 1990. The dynamics of estuarine macrophytes in relation to flood/siltation cycles. Botanica Marina 33(2):159-164.
Talbot, M.M.B. and Bate, G.C. 1987. The Distribution and Biomass of the Seagrass Zostera capensis in a Warm-temperate Estuary. Botanica Marina 30(1):91-99.
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Citation | | Adams, J. & van der Colff, D. 2018. Zostera capensis Setch. National Assessment: Red List of South African Plants version . Accessed on 2024/09/14 |
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