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TheMarine biodiversity of South Africa is the variety of living organisms that live in the seas off the coast ofSouth Africa. It includesgenetic, species andecosystemsbiodiversity in a range of habitats spread over a range of ecologically varied regions, influenced by thegeomorphology of the seabed and circulation of major and localwater masses, which distribute both living organisms and nutrients in complex and time-variable patterns.
South Africa has a wide range of marine diversity with coastline in three oceans, two major current systems, major ocean frontal systems and benthic topography extending to a maximum depth of 5 700 m. There are 179 defined marine ecosystem types, 150 of them around South Africa and 29 around the sub-Antarctic territory of the Prince Edward Islands.[1]
Research on biodiversity of South African waters started in the colonial period from the late 18th century to the late 19th century, with shipboard survey and collection expeditions, like theChallenger,Deutsche Tiefsee andDiscovery expeditions. From the early 20th century to the 1970s a group of local marine taxonomists such asJ.D.F. Gilchrist andK.H. Barnard, described most of the common fauna on a morphological basis, and after 1970 marine research shifted to ecological aspects and taxonomy was largely neglected. This has left the region with a shortage of taxonomic expertise in comparison with most of the developed world.[2]: 21
TheSeaKeys project was started in 2014 to help develop foundational marine biodiversity knowledge by addressing some of the more significant gaps. The project had some success in collating species checklists and records, and national inventories covering over 9700 species in various groups were compiled. Data sets were digitised, distribution data updated for fish and benthic invertebrates, and a guide to offshore marine invertebrates was published. This project highlighted the deficit in taxonomic skills, as it became apparent that most of the guides and lists had not changed much since the 1970s.[2]: 22
The National Biodiversity Assessment (NBA) is recurring project by the South African National Biodiversity Institute in collaboration with the Department of Environmental Affairs and several other organisations to assess the state of South Africa's biodiversity over time as an input for policy and decision making where the environment may be affected. The NBA looks into genetic, species and ecosystems biodiversity for terrestrial, freshwater, estuarine and marine environments. Each assessment cycle takes approximately five years, and both generates new knowledge and analyses existing knowledge.[3] NBA reports are named for the year of the data, and are usually published in the following year. They have been published for 2004,[4] 2011,[5] and 2018,[2] and include reports, data, and supplementary documents.[6]
Physical oceanography is the sub-domain ofoceanography which focuses on the study of physical conditions and processes within the ocean, including the physical properties and circulation of ocean waters. These matters influence the biodiversity by providing the setting in which the ecology and biodiversity evolve.
The physical setting for the biodiversity of the South African coastal and offshore waters is mainly temperate continental shelf, slope and abyss in the South Atlantic and South-west Indian Oceans off the southern part of the continent of Africa. The geomorphology of this region has local effects on the ocean circulation, particularly effects on ocean currents and upwellings, which in turn affect the distribution of organisms and the environment in which they live.
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Thecontinental shelf of southern Africa varies considerably in width along the coast, and the shelf edge also varies in depth. To the north-east the shelf is narrow to very narrow, with a relatively shallow break, but it is much wider over theAgulhas Bank off the southern tip of the continent. This gradual increase in width affects the path of the powerfulAgulhas Current, pushing it further offshore towards theSouthern Ocean.
The Agulhas Current is the western boundary current of the southwest Indian Ocean. It flows south along the African east coast and along the south-eastern edge of the bank. It thenretroflects back into the Indian7 Ocean south-west of the bank. This retroflection results in intenseeddy activities such as meanders, eddies, and filaments.[7] In upper layer water, the Agulhas rings and eddies move warm and salty water into the large South Atlanticgyre, which exports it to the tropics. In the lower ocean layers water is transported in the opposite direction.[8]
The Agulhas acts as an oceanicconvergence zone. Due tomass continuity this drives surface waters down, resulting in theupwelling of cold, nutrient rich water south of the current. Additionally, the convergence tends to increase the concentration of plankton in and around the Agulhas. Both of these factors result in the area being one of enhancedprimary productivity as compared to the surrounding waters. This is especially notable in the Agulhas Retroflection waters, where chlorophyll-a concentrations tend to be significantly higher than the surrounding South Indian Ocean and South Atlantic Ocean waters.[9]Warm core rings are known to have lower primary productivity than surrounding cold waters. Agulhas Rings have been observed to carry waters with lowchlorophyll-a concentration into theSouth Atlantic. The size ofphytoplankton in Agulhas Rings tends to be smaller than in the surrounding water (around 20 μm in diameter).[9] Agulhas Rings have also been observed as removing larval and juvenile fish from the continental shelf.
The Benguela Current is the broad, northward flowingocean current that forms the eastern portion of theSouth AtlanticOcean gyre. The current extends from roughlyCape Point in the south, to the position of theAngola-Benguela front in the north, at around 16°S. The current is driven by the prevailing south easterly trade winds. Inshore of the Benguela Current proper, the south easterly winds drivecoastal upwelling, forming theBenguela Upwelling System . The cold, nutrient rich waters that upwell from around 200–300 m depth in turn fuel high rates of phytoplankton growth, and sustain the productive Benguela ecosystem.
Upwelling is anoceanographic phenomenon that involveswind-driven motion ofsurface water away from the coast, which is replaced by a flow of deeper dense, cooler, and usuallynutrient-rich water towards theocean surface, The nutrient-rich upwelled water stimulates the growth and reproduction ofprimary producers such asphytoplankton. Due to thebiomass of phytoplankton and presence of cool water in these regions, upwelling zones can be identified by coolsea surface temperatures (SST) and high concentrations ofchlorophyll-a.[10][11] The increased availability of nutrients in upwelling regions results in high levels ofprimary production. Upwellings that are driven by coastalcurrents or diverging open ocean have the greatest impact on nutrient-enriched waters and global fishery yields.[12][9]
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The marine ecoregions of the South African exclusive economic zone are a set of geographically delineated regions of similar ecological characteristics on a fairly broad scale, covering the exclusive economic zone along the South African coast. There were originally five inshore bioregions over the continental shelf and four offshore bioregions covering the continental slope and abyssal regions. These bioregions are used for conservation research and planning. They were defined in the South African National Spatial Biodiversity Assessment of 2004.[4] The South African National Spatial Biodiversity Assessment of 2011 amended this to reduce the number of regions to four inshore and two offshore and rename them as ecoregions.[5]
A total of 136 marine habitat types have been identified. These include 37 coastal habitat types, 17 inshore habitat types in the 5 to 30 m depth range, 62 offshore benthic habitat types deeper than 30 m, and 16 offshore pelagic habitat types,[13] three types of island and one type of lagoon.[5]
Endemism is theecological state of aspecies or other taxonomic group being native to a single defined geographic location, such as an island, country or other defined zone, orhabitat type; organisms that areindigenous to a place are not endemic to it if they are also found elsewhere. The extreme opposite of an endemic species is one with acosmopolitan distribution, having a global or widespread range. Although the specific drivers of endemism are unclear, physical, climatic and biological factors can contribute to endemism. Endemic species can easily become endangered or extinct if their already restricted habitat changes, particularly—but not only—due to human actions, including the introduction of new species.
Over 13000 species of marine organisms are recorded from South African waters. Endemism is estimated at between 26 and 33%, the third highest marine endemism after New Zealand (51%) and Antarctica (45%). This varies between taxonomic groups from no endemic marine mammals or birds, to over 90% ofchitons.[2]: 20
The region of highest known endemism is the south coast Agulhas inshore ecoregion, which is relatively far from the national borders, and relatively isolated from large scale oceanic circulation due to the effects of the widening of the continental shelf at the Agulhas Bank on the path of the Agulhas current, and far from other warm temperate regions. This region is largely bypassed by the Agulhas current, and has cooler inshore water due to upwelling, making it less hospitable to tropical Indo-west Pacific species. It is also isolated from the South Atlantic and Southern Ocean, so has been more prone to niche speciation.[2]: 20
| This sectionneeds expansion with: Distribution of South African and southern African endemic marine organisms. You can help byadding to it.(August 2020) |
Marine animals
Seaweeds
Prokaryotes
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Biodiversity protection is one of the priorities of the network of marine protected areas of South Africa.[14]
A marine protected area of South Africa is an area of coastline or ocean within theexclusive economic zone (EEZ) of the Republic ofSouth Africa that is protected in terms of specific legislation for the benefit of the environment and the people who live in it and use it.[15] An MPA is a place where marine life can thrive under less pressure than unprotected areas, like underwater parks, and this healthy environment can benefit neighbouring areas.[16][17]
There are a total of 45marine protected areas in the South African EEZ, with a total area of 5% of the waters as of 2019. The target was to have 10% of the oceanic waters protected by 2020. All but one of the MPAs are in the exclusive economic zone off continental South Africa, and one is offPrince Edward Island in theSouthern Ocean.
People can take part in a wide range of non-consumptive activities in all of South Africa's MPAs, and some parts of some MPAs are zoned for limited consumptive activities.[17] Some of these activities require a permit, which is a form of taxation.
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Field guides:
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