Zostera capensis explained

Zostera capensis is a species of dwarf eelgrass growing along the shores of the Indian and Atlantic oceans on the African coast. Its range extends from southern Kenya, through Tanzania, Mozambique, Madagascar, and South Africa up to Angola .^{[1] [2] [3]} This species is the dominant seagrass species in South Africa, occurring as fragmented populations along the coast and occupying subtidal and intertidal habitats in shallow bays, estuaries and lagoons. The two largest meadows in South Africa are present in the Knysna lagoon and Berg river estuary. When last mapped in 2007, Zostera capensis cover in the Berg river estuary was estimated at 206 hectares,^[4] while in 2019 the Knysna lagoon was mapped at 316 hectares.^[5] Further north in its distribution, Maputo bay in Mozambique is an important habitat for this species, containing approximately 4016 hectares of mixed Zostera capensis and Halodule wrightii on muddy flats.^[6] Over its total distribution, this species is estimated to occupy less than 2000 km².

Threats

Zostera capensis can grow fast, but it is a slow colonizer, with numerous anthropogenic threats.^[4] Populations of Zostera capensis are threatened by nutrient enrichment (i.e., eutrophication) ^{[4] [7] [8]} which affect their physiological performances by increasing epiphytic fouling/loading;^[8] these epiphytic fouling are strongly associated with lower shoot survival.^[9] In addition, flooding of estuarine areas, pollution and sedimentation also present major threats to Z. capensis; bioturbation also poses a negative impact on populations with lower biomass and highly fragmented patches.^[4] In Mozambique, shellfish harvesting (i.e., gleaning) has been reported as one of the major threats to Z. capensis. Nonetheless, Z. capensis remains a poorly protected yet severely fragmented keystone species ^{[4] [10] [11]}

Notes and References

1. William Albert Setchell. 1933. Proc. Natl. Acad. Sci. U.S.A. 19: 815
2. Toml. & Posl., Taxon 50: 432 (2001), Nanozostera capensis
3. Web site: Zostera capensis. . . 2015-08-11.
4. Distribution and status of Zostera capensis in South African estuaries — A review . Adams, J. B . South African Journal of Botany . 2016 . 107 . 63–73 . 10.1016/j.sajb.2016.07.007. free .
5. Mapping subtidal estuarine habitats with a remotely operated underwater vehicle (ROV) . Wasserman, J . African Journal of Marine Science . 2020 . 42 . 1 . 123–128 . 10.2989/1814232X.2020.1731598. 219002032 .
6. Book: Bandeira . Salomão . Bandeira . S . Paula . J . The Maputo Bay Ecosystem . Chapter 8.1 : Zostera capensis - a vulnerable seagrass species . 2014 . WIOMSA . Zanzibar Town . 171–173 . 978-9987-9559-3-0.
7. Human, L.R.D. Snow, G.C. Adams, J.B. Bate, G.C. Yang, S.C. 2015. The role of submerged macrophytes and macroalgae in nutrient cycling: a budget approach Estuarine, Coastal and Shelf Science, Coastal and Shelf Science, 154, pp. 169-178
8. Mvungi, E. F., and Pillay, D. 2019. Eutrophication overrides warming as a stressor for a temperate African seagrass (Zostera capensis). PLOS ONE 14:e0215129. doi: 10.1371/journal.pone.0215129
9. Ceccherelli G, Oliva S, Pinna S, Piazzi L, Procaccini G, Marin-Guirao L, et al. 2018. Seagrass collapse due to synergistic stressors is not anticipated by phenological changes. Oecologia. 186: 1137–1152.
10. Phair, N. L., Toonen, R. J., Knapp, I., & von der Heyden, S. 2019. Shared genomic outliers across two divergent population clusters of a highly threatened seagrass. PeerJ, 7, e6806. https://doi.org/10.7717/peerj.6806
11. Phair, L.N. Toonen, R.J. Knapp, I.S. von der Heyden, S. 2020. Anthropogenic pressures negatively impact genomic diversity of the vulnerable seagrass Zostera capensis Journal of Environmental Management 255: 109831