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Orange Cone

The Orange Cone is a transboundary EBSA shared between Namibia and South Africa that spans the mouth of the Orange River: South Africa’s most major river in terms of run-off to the marine environment. It is regionally rare in that comparable habitats are not encountered for 300 km south (Olifants River) and over 1300 km north (Kunene River) of this system. The estuary is biodiversity-rich but modified, and the coastal area includes a Critically Endangered habitat type. The pelagic environment has cold waters with high productivity/chlorophyll levels due to upwelling. However, slow, variable currents and weaker winds make it potentially favourable for reproduction of pelagic species, and it likely plays a key role in fish recruitment. This EBSA is also a transboundary Ramsar site, and an Important Bird Area.

EBSA Description: Orange Cone

General Information

Summary

The Orange Cone is a transboundary area between Namibia and South Africa that spans the mouth of the Orange River (South Africa and Namibia’s major river in terms of run-off to the marine environment). The estuary is biodiversity-rich but modified, and the coastal area includes many Critically Endangered, Endangered, and Vulnerable habitat types (with the area being particularly important for the Critically Endangered Namaqua Sandy Inshore, Namaqua Inshore Reef and Hard Grounds and Namaqua Intermediate and Reflective Sandy Beach habitat types). The marine environment experiences slow, but variable currents and weaker winds, making it potentially favourable for reproduction of pelagic species. Furthermore, given the proven importance of river outflow for fish recruitment at the Thukela Banks (a comparable shallow, fine-sediment environment on the South African east coast), a similar ecological dependence for the inshore Orange Cone is likely. Evidence supporting this hypothesis is growing, but has not yet been consolidated. Comparable estuarine/inshore habitats are not encountered for 300 km south (Olifants River) and over 1300 km north (Kunene) of this system. The Orange River Mouth is a transboundary Ramsar site between Namibia and South Africa. The river mouth also falls within the Tsau//Khaeb (Sperrgebiet) National Park in Namibia, is under consideration as a protected area by South Africa, and is also an Important Bird and Biodiversity Area. Although there are substantially impacted areas especially on the coast and in the estuary, much of the area remains in a natural state. In summary, this area is highly relevant in terms of: ‘Uniqueness or rarity’, ‘Importance for threatened, endangered or declining species and/or habitats’ and ‘Special importance for life history stages of species’.

MARISMA updates

 The site description has been updated and criteria ranks revised; the EBSA boundaries have been refined.

Introduction of the area

The Orange Cone spans the coastal boundary between South Africa and Namibia. The Orange River estuary extends approximately 10 km inland of the sea in a hydrological sense, although estuarine-dependent species migrate much further upstream. The estuary is substantially modified but under rehabilitation. Boundaries of the marine area that is ecologically coupled to the estuary are not accurately known, but could be extensive: seasonally and inter-annually, the marine habitat affected by freshwater outflow varies from a few kilometres to hundreds of kilometres in the longshore direction during floods, particularly southwards (Shillington et al., 1990). This area is located 50 km north and south of the Orange River, extending 30 - 45 km offshore, and includes the full extent of the estuary. There are 16 marine and coastal ecosystem types represented in the area (Sink et al., 2012, 2019; Holness et al., 2014). The associated pelagic environment is characterized by upwelling, giving rise to cold waters with high productivity/chlorophyll levels (Lagabrielle 2009). However, the winds in the area are weaker compared to that to the north or south of the river mouth, leading to less local upwelling (Boyd, 1988). The site is presented as a Type 1 EBSA because it contains "Spatially stable features whose positions are known and individually resolved on the maps" (sensu Johnson et al., 2018).

Description of location

The Orange River estuary is located at 29°S and forms the boundary between South Africa and Namibia. The northern and southern boundaries of the Orange Cone EBSA are located 50 km north and south of the Orange River, respectively, with the eastern boundary extending 30 – 45 km offshore, and includes the full extent of the estuary. However, the broader area has characteristics of the Orange Cone marine environment as far as 100 km offshore. This EBSA straddles coastal and marine areas within the national jurisdictions of South Africa and Namibia.

 

Area details

Feature description of the area

There are 16 ecosystem types represented in this EBSA (Sink et el., 2012, 2019; Holness et al., 2014). The associated pelagic environment is characterized by upwelling, giving rise to cold waters with high productivity (Lagabrielle 2009). However, the winds in the Orange Cone are weaker than those north or south of the area, leading to some stratification (Boyd 1988). Moreover, currents in the inshore region, and indeed over much of the Orange Cone area, have slower speeds than those occurring further north or south, and movements in both upper and lower layers are dominated by diurnal and/or inertial motions (Iita et al., 2001, Largier and Boyd, 2001).

The river and estuary have received substantial research attention over the last decade; the adjacent marine environment much less so, apart from some research during the Large Marine Ecosystem (LME) project from 1995-2000. However, given the proven role of the Thukela River outflow for the recruitment of fish stocks in the adjacent marine area on the South African east coast (Turpie and Lamberth 2010), it is hypothesized that the Orange River plays a similar role on the South African west coast. Although not formally described, evidence is mounting to support this hypothesis, because there are seemingly many relationships between Orange River flow volumes and demersal, pelagic and nearshore fish biomass (S.J. Lamberth, pers.com, unpublished). For example, the sole fishery collapse was associated with a change in local sediment particle size, because it altered burying difficulty and exposure to predators. Also, anchovy (mostly juveniles) appear to be positively correlated with the size of the plume, because the plume probably serves as a turbidity refuge. Furthermore, the conditions in the area are consistent with the criteria proposed for supporting pelagic species' reproduction (Parrish et al., 1983).

Because of a previous lack of research, the boundaries of the marine zone that is ecologically coupled to the estuary were not accurately known, but were thought to be extensive. For example, geological research suggests that the sediment from the Orange River travels as far north as southern Angola (1750 km north of the mouth), and makes up >80% of the dune sand along the Skeleton Coast in Namibia (Garzanti et al., 2014); according to these authors, "this is the longest cell of littoral sand transport documented so far". A particular challenge to determining the river's extent of influence is that the marine habitat affected by freshwater outflow varies greatly both seasonally and inter-annually, from a few to hundreds of kilometres in the longshore direction (mainly southwards) during floods (Shillington et al., 1990). Submarine delta deposits off the mouth of the Orange River extend 26 km offshore, and 112 km alongshore (Rodgers & Rau 2006). The terrigenous material exiting the Orange River has a heterogeneously integrated catchment signal (Hermann et al., 2016) that is generally confined to about 50 km from the shore (Rodgers & Rau 2006). Since the original description of this EBSA, recent work on marine sediments and delineation of muddy sediment associated habitats have allowed a far more accurate delineation of the Orange Cone (Karenyi, 2014; Karenyi et al., 2016). It is largely these new data that were used to refine the Orange Cone EBSA boundary, which was noted in the original description as being an approximation that needed further research so it could be properly delineated. New, fine-scale coastal mapping (Harris et al., 2019) also allowed a more accurate coastal boundary to be delineated, with other recent data also included (e.g., Holness et al., 2014; Sink et al., 2012, 2019).

In terms of uniqueness of habitat (i.e., refuge for estuarine-dependent or partially dependent fish, and birds), approximately similar estuarine and adjacent inshore habitats are not encountered for over 300 km further south to the Olifants River and over 1300 km further north, until the Kunene River (Lamberth et al., 2008, van Niekerk et al., 2008). The fact that the estuary is a declared Ramsar site (Ramsar 2013; note that the adjacent Namibian and South African Ramsar sites were joined into a transboundary site) and an Important Bird and Biodiversity Area (IBA; BirdLife International 2013) is an important recognition of its importance to birds as well as other species. Altogether, 206 species have been recorded in the EBSA, including 4 threatened fish and condricthian species (OBIS 2017).

Feature conditions and future outlook of the proposed area

The impact of reduced and altered flow at the estuary mouth and into the marine environment has had a negative impact on the estuarine habitat, including the salt marsh, which was exacerbated by inappropriate developments associated with mining at the site (van Niekerk and Turpie 2012). The impact of these changes on the marine offshore environment is not yet known. Both the flow regime (as it will reach the mouth and the marine area) and rehabilitation of the estuary and salt marsh area need to be addressed. However, an estuary management plan is in an advanced stage, and protected area status for the estuary is well advanced as well (van Niekerk and Turpie 2012). Regarding the marine and coastal habitats and biodiversity of the area, the coastline and inshore area to 30 m depth is under considerable threat from mining impacts and is currently unprotected (Sink et al., 2012).

Ecosystem threat status has been estimated in South Africa (Sink et al., 2012, 2019) and Namibia (Holness et al., 2014; Table in the Other relevant website address or attached documents section) by assessing the weighted cumulative impacts of various pressures (e.g., extractive resource use, pollution, development and others) on each ecosystem type. These include two Critically Endangered, four Endangered and four Vulnerable ecosystem types, and another one ecosystem type that is Vulnerable. The Critically Endangered status implies that very little (<= 20%) of the total area of the habitats assessed are in natural/pristine condition, and it is expected that important components of biodiversity pattern have been lost and that ecological processes heavily modified. However, within the area, much of the EBSA was assessed to be in good ecological condition (56%), some fair (33%), and a lesser extent (11%) in poor ecological condition.

 

Assessment of the area against CBD EBSA criteria

 Uniqueness or rarity

 

Rank: High

In terms of habitat uniqueness (i.e., refugia for estuarine-dependent or partially estuarine-dependent fish and birds, and freshwater outflow to the marine environment), approximately similar estuarine and adjacent inshore habitat are not encountered for over 300 km further south to the Olifants River, and over 1300 km further north, until the Kunene River (van Niekerk et al., 2008, Lamberth et al., 2008). The marine area is fed by the estuarine outflow, and also has its own oceanographic characteristics in terms of inertial currents and stratification, thus being largely "sheltered" from Benguela System forcing (Boyd 1988, Largier and Boyd 2001) that influences the whole Benguela region. This system is also the longest cell of littoral sand transport that has been recorded to date, with sediment moving as much as 1750 km north to southern Angola, and providing 80% of the sand that comprises the dunes along the Namibian Skeleton Coast (Garzanti et al., 2014).

 Special importance for life-history stages of species

 

Rank: High

A total of 33 fish species from 17 families have been captured from the Orange River estuary (van Niekerk et al., 2008). Out of these species, 34 % showed some degree of estuarine (i.e., euryhaline) dependence, 24 % were marine and the remaining 42 % were freshwater species. The high diversity and abundance of estuarine-dependant and marine species suggests that this is an extremely important estuarine nursery area, especially for Kob species (van Niekerk and Turpie 2012), and not just a freshwater conduit as previously thought (van Niekerk et al., 2008). Certainly, oceanographic conditions in the area are consistent with the criteria proposed by Parrish et al. (1983) for the reproduction of pelagic species, and the system is also hypothesised to play a similar role to that of the comparable Thukela River/Thukela Banks (on the South African east coast) where the freshwater outflow is proven to support recruitment of fish stocks (Turpie and Lamberth 2010). Evidence is continually mounting to confirm the role of the Orange Cone in supporting key life-history stages. For example, the area is the northern margin of the important west coast nursery ground for pelagic fish species with periodic spawning (Hutchings et al., 2002). The Orange Cone is also an important recruitment/nursery area and one of three primary population components for shallow water hake (Jansen et al., 2016). Furthermore, northern sections of the Orange Cone, particularly a coastal reef called “Mittag”, are important for the Namibian commercial rock lobster fishery (Currie et al., 2008).

The estuary and wetland area are also an important stopover site for migrating shorebirds and other waterbirds, and provides breeding habitat for birds such as White-breasted Cormorants (Crawford et al., 2013) and Cape Cormorants. However, due to the destruction of breeding islands by the 1988 flood, the latter have not bred there since (H. Kolberg pers. obs). The value of the site is recognised internationally with both Ramsar and IBA status. In fact, the Orange River Mouth Wetlands are said to be the sixth most important coastal wetlands for birds, supporting as many as 26000 individuals of 56 species (BirdLife International, 2018).

South of the Kunene River (over 1300 km to the north of the Orange River), the only permanently open estuaries on the west coast of the sub-region include the Orange, Olifants and Berg Rivers (Lamberth et al., 2008). Migration up and down the west coast of southern Africa by marine and estuarine species, e.g., Angolan dusky kob, and west coast steenbras, may be dependent on the availability of warm water refugia offered by these estuary mouths and their plumes, especially during upwelling months (Lamberth et al., 2008).

 Importance for threatened, endangered or declining species and/or habitats

 

Rank: High

The area is also an important nursery for coastal fish species, such as kob (van Niekerk and Turpie 2012) which are overexploited (Mann 2000). The estuary includes important breeding habitat for Endangered Cape Cormorants (Crawford et al., 2016), and also contains Endangered Ludwig’s bustard and Vulnerable Damara Terns (Birdlife International, 2018). Four fish and condricthian species recorded in the EBSA are threatened, including the Endangered Rostroraja albai and Mustelus mustelus, and Vulnerable Galeorhinus galeus and Squalus acanthias (OBIS 2017).

Ten of the 16 ecosystem types represented in this EBSA are threatened, including two Critically Endangered, four Endangered and four Vulnerable ecosystem types (Holness et al., 2014; Sink et al., 2019). Because ecosystem types are generally a very good surrogate for species-level biodiversity patterns, the implication, therefore, is that the species and biological communities that are associated with and unique to these habitats are similarly declining and threatened.

 Vulnerability, fragility, sensitivity, or slow recovery

 

Rank:  Medium

The estuarine salt marsh area is vulnerable and has been slow to show recovery despite rehabilitation efforts (van Niekerk and Turpie 2012). There has also been a marked decline in certain fish stocks that were previously exploited in the region (Lamberth et al., 2008). Mining and habitat modification are thought to have had an impact with respect to these changes.

 Biological productivity

 

Rank: Medium

Winds in the Orange Cone are weaker than those which occur to the north or south of the area, leading to some stratification (Boyd 1988). This, and the effect of the fresh water inflow, may serve to concentrate productivity within the area.

 

 Biological diversity

 

Rank: Medium

Altogether, 206 species have been recorded in the Orange Cone EBSA (OBIS 2017). A high diversity of fish species (33 species from 17 families) has been captured from the Orange River estuary (van Niekerk et al., 2008), including freshwater, marine and estuarine-dependent species. The marine area served as the conduit supporting the estuary's biodiversity for migratory marine and estuarine-dependent species, as well as marine pelagic and demersal species, including their juvenile stages. Furthermore, the fact that the estuary is a declared Ramsar site (Ramsar 2013) and an IBA (BirdLife International 2013) are important recognitions of its importance to birds and other species. There are 16 ecosystem types represented in this EBSA (Holness et al., 2014; Sink et al., 2019).

 

 Naturalness

 

Rank: Medium

The estuary and nearshore are impacted, including notable infestation by alien plants around the estuary that persist in spite of rehabilitation efforts. Nevertheless, the estuary still provides many ecological services such as recruitment. There are significant impacts from coastal diamond mining in Namibia and, to a lesser extent, in South Africa (Sink et al., 2012; Holness et al., 2014). Although data are sparse, the area has been shown to be largely in fair condition (Sink et al., 2012; Holness et al., 2014), but there have been long-term declines in fish catch.

 

References

Anderson, M.D., Kolberg H., Anderson P.C., Dini J., Abrahams A. 2003. Waterbird populations at the Orange River mouth from 1980 – 2001: a re-assessment of its Ramsar status. Ostrich, 74: 1-14.

BirdLife International. 2013. Important Bird Areas: ZA023 Orange River mouth wetlands. URL: www.birdlife.org/datazone/sitefactsheet.php?id=7098 [accessed on 22 April 2013]

Boyd, A. J. 1988. The Oceanography of the Namibian Shelf. PhD Thesis University of Cape Town. 190 pp.

Currie H., Grobler K., Kemper, J. 2008. Concept note, background document and management proposal for the declaration of Marine Protected Areas on and around the Namibian islands and adjacent coastal areas.

Crawford, R.J.M., Randall, R.M., Whittington, P.A., Waller, L., Dyer, B.M., Allan, D.G., Fox, C., Martin, A.P., Upfold, L., Visagie, J., Bachoo, S., Bowker, M., Downs, C.T., Fox, R., Huisamen, J., Makhado, A.B., Oosthuizen, W.H., Ryan, P.G., Taylor R.H., Turpie, J.K. 2013. South Africa's coastal-breeding white-breasted cormorants: population trends, breeding season and movements, and diet. African Journal of Marine Science, 35: 473-490.

Crawford, R.J.M., Randall, R.M., Cook, T.R., Ryan, P.G., Dyer, B.M., Fox, R., Geldenhuys, D., Huisamen, J., McGeorge, C., Smith, M.K., Upfold, L., Visagie, J., Waller, L.I., Whittington, P.A., Wilke, C.G., Makhado, A.B. 2016. Cape cormorants decrease, move east and adapt foraging strategies following eastward displacement of their main prey. African Journal of Marine Science, 38: 373-383.

Garzanti, E., Vermeesch, P., Andò, S., Lustrino, M., Padoan, M., Vezzoli, G. 2014. Ultra-long distance littoral transport of Orange sand and provenance of the Skeleton Coast Erg (Namibia), Marine Geology, 357: 25-36.

Harris, L.R., Bessinger, M., Dayaram, A., Holness, S., Kirkman, S., Livingstone, T.-C., Lombard, A.T., Lück-Vogel, M., Pfaff, M., Sink, K.J., Skowno, A.L., Van Niekerk, L., 2019. Advancing land-sea integration for ecologically meaningful coastal conservation and management. Biological Conservation 237, 81-89.

Herrmann, N., Boom, A., Carr, A.S., Chase, B.M., Granger, R., Hahn, A., Zabel, M., Schefuß, E. 2016. Sources, transport and deposition of terrestrial organic material: A case study from southwestern Africa. Quaternary Science Reviews, 149: 215-229.

Holness S., Kirkman S., Samaai T., Wolf T., Sink K., Majiedt P., Nsiangango S., Kainge P., Kilongo K., Kathena J., Harris L., Lagabrielle E., Kirchner C., Chalmers R., Lombard M. 2014. Spatial Biodiversity Assessment and Spatial Management, including Marine Protected Areas. Final report for the Benguela Current Commission project BEH 09-01.

Hutchings, L., Beckley, L.E., Griffiths, M.H., Roberts, M.J., Sundby, S., van der Lingen, C. 2002. Spawning on the edge: spawning grounds and nursery areas around the southern African coastline. Marine and Freshwater Research, 53: 307-318.

Iita, A., Boyd, A.J., Bartholomae, C.H. 2001. A snapshot of the circulation and hydrology of the southern and central shelf regions of the Benguela Current in winter 1999. South African Journal of Science, 97: 213–217.

Jansen, T., Kristensen, K., Kainge, P., Durholtz, D., Strømme, T., Thygesen, U.H., Wilhelm, M.R., Kathena, J., Fairweather, T.P., Paulus, S., Degel, H., Lipinski, M.R., Beyer, J.E. 2016. Migration, distribution and population (stock) structure of shallow-water hake (Merluccius capensis) in the Benguela Current Large Marine Ecosystem inferred using a geostatistical population model. Fisheries Research, 179: 156–167.

Johnson, D.E., Barrio Froján, C., Turner, P.J., Weaver, P., Gunn, V., Dunn, D.C., Halpin, P., Bax, N.J., Dunstan, P.K., 2018. Reviewing the EBSA process: Improving on success. Marine Policy 88, 75-85.

Karenyi, N. 2014. Patterns and Drivers of Benthic Macrofauna to Support Systematic Conservation Planning for Marine Unconsolidated Sediment. Nelson Mandela Metropolitan University, Port Elizabeth.

Karenyi, N., Sink, K., Nel, R. 2016. Defining seascapes for marine unconsolidated shelf sediments in an eastern boundary upwelling region: The southern Benguela as a case study. Estuarine, Coastal and Shelf Science, 169: 195-206.

Lagabrielle E. 2009. Preliminary report: National Pelagic Bioregionalisation of South Africa. Cape Town: South African National Biodiversity Institute.

Lamberth, S.J., Van Niekerk, L., Hutchings, K. 2008. Comparison of, and the effects of altered freshwater inflow on, fish assemblages of two contrasting South African estuaries: the cool-temperate Olifants and the warm-temperate Breede. African Journal of Science, 30: 331–336.

Mann BQ. 2000. Status Reports for Key Linefish Species. Durban: Oceanographic Research Institute Special Publication

OBIS. 2017. Summary statistics of biodiversity records in the Orange Cone EBSA. (Available: Ocean Biogeographic Information System. Intergovernmental Oceanographic Commission of UNESCO. www.iobis.org. Accessed: 2017-07-27).

Parrish, R.H., A. Bakun, D.M. Husby, and C.S. Nelson. 1983. Comparative climatology of selected environmental processes in relation to eastern boundary current pelagic fish reproduction. p. 731-778. In: G.D. Sharp and J. Csirke (eds.) Proceedings of the Expert Consultation to Examine Changes in Abundance and Species Composition of Neritic Fish Resources. FAO Fish. Rep. 291(3), 1224 pp.

Ramsar. 2013. Orange River Mouth, Ramsar site no. 526. The annotated Ramsar list: South Africa. URL: www.ramsar.org/cda/en/ramsar-documents-list-anno-southafrica/main/ramsar [accessed on 22 April 2013]

Rodgers, J., Rau, A.J. 2006. Surficial sediments of the wave-dominated Orange River Delta and the adjacent continental margin off south-western Africa. African Journal of Marine Science, 28: 511-524.

Shillington, F.A., Brundrit, G.B., Lutjeharms, J.R.E., Boyd, A.J., Agenbag, J.J., Shannon, L.V. 1990. The coastal current circulation during the Orange River flood 1988. Transaction of the Royal Society of South Africa, 47: 308-329.

Sink, K., Holness, S., Harris, L., Majiedt, P., Atkinson, L., Robinson, T., Kirkman, S., Hutchings, L., Leslie, R., Lamberth, S., Kerwath, S., von der Heyden, S., Lombard, A., Attwood, C., Branch, G., Fairweather, T., Taljaard, S., Weerts, S., Cowley, P., Awad, A., Halpern, B., Grantham, H., Wolf, T. 2012. National Biodiversity Assessment 2011: Technical Report. Volume 4: Marine and Coastal Component. South African National Biodiversity Institute, Pretoria.

Sink, K.J., van der Bank, M.G., Majiedt, P.A., Harris, L.R., Atkinson, L., Karenyi, N., Kirkman, S. (eds) 2019. National Biodiversity Assessment 2018 Technical Report Volume 4: Marine Realm. South African National Biodiversity Institute, Pretoria. http://hdl.handle.net/20.500.12143/6372.

Turpie, J., Lamberth, S.J. 2010. Characteristics and value of the Thukela Banks crustacean and linefish fisheries, and the potential impacts of changes in river flow. African Journal of Marine Science, 32: 613-624.

van Niekerk, L., Neto, D.S., Boyd, A.J., Holtzhausen, H. 2008. BCLME Project BEHP/BAC/03/04: Baseline Surveying of Species and Biodiversity in Estuarine Habitats. Benguela Environment Fisheries Interaction & Training Programme and Instituto Nacional de Investigacao Pesqueira. 152 pp.

Van Niekerk, L. and Turpie, J.K. (eds). 2012. South African National Biodiversity Assessment 2011: Technical Report. Volume 3: Estuary Component. CSIR Report Number CSIR/NRE/ECOS/ER/2011/0045/B. Council for Scientific and Industrial Research, Stellenbosch.

Select the icon in the top right corner of the map to view the EBSA delineation in full-screen mode.

 

Orange Cone

EBSA criteria met at a high (red), medium (orange) or low (yellow) rank. Stars indicate criteria changes, coloured by the previous rank.

 

Download the revised EBSA description:

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