The marine animals of the Cape Peninsula are a diverse and highly endemic group. The rich waters off the Cape Peninsula of South Africa support many different invertebrate animals[1], which in turn support many predators, the most notorious of which being the great white shark. Many species of marine animal are found only in the nutrient-rich waters around the peninsula [2][citation needed]. Biodiversity is high. Also, even though much research effort has been directed at Cape waters, new species are still being discovered[3],[4].
Habitats edit
The peninsula has a particularly varied marine environment. The western side of the peninsula, known as the Atlantic side, is marked by kelp forests with a wide array of invertebrate life living in their understoreys, from hard corals to lacy bryozoans, lobsters and nudibranchs. Hairy crabs camouflaged with sponges and basket stars are common. The water is cold, typically in the range of 8-14°C, and usually at the lower end of the range after a strong south east wind, as a result of deep water upwelling. The Atlantic side is often subject to storm waves, so the animal life is fairly resilient.
On the eastern side of the peninsula is False Bay. Marine life is rather different because the peninsula shelters the bay from the north west storms of winter which affect the Atlantic coast. Temperatures in the bay very rarely fall below 11°C, and the normal range is between 12-16°C, with occasional forays into the 18-20°C range in summer. The calmer waters and higher temperatures of False Bay provide a habitat for a wider range of animals. Cow sharks hunt for lobsters and octopus in the shallow-water kelp forests and juvenile seals are the favoured food of the great white shark.
Images:- Clinus superciliosus, Clinus venustris - Cape fur seal - Multi-coloured sea fan - Hottentot - Bonisa nakaza, Janolus capensis, Tambja capensis, Polycera spp. - Kelp
Oceanography and seasonal variations edit
The difference in reef life on the two sides of the peninsula is the result of physical forces. In summer a high pressure zone known as the South Atlantic High establishes itself over the ocean west of the Cape Peninsula. Winds generated by this pressure zone reach the Cape from the south east. On the western side of the peninsula, strong winds blow offshore, driving inshore surface water north and away from the coast. This allows offshore water to well up from the depths. This deep water is rich in nutrients, having upwelled from regions away from sunlight and hence with no plant life. It is also cold. Since the coast slopes steeply into the ocean on the western side of the peninsula, deep water can upwell fast when driven by the south east wind, and temperatures can drop by degrees in a matter of hours. Once at the surface, phytoplankton (tiny photosynthetic organisms) bloom, stimulated by sunlight and the nutrient-rich water, generating a rich soup of floating food[5].
The south east wind also causes upwelling at Cape Hangklip. This upwelled water then flows into False Bay. It is a slower influx of nutrients, since inshore water cannot easily be blown offshore in the bay, because of the barrier created by the peninsula. Hence water retention times in the bay are relatively long. The nutrient-rich upwelled water in the shallow bay is warmed by the summer sun, and, being well aerated by wave action, supports impressive phytoplankton blooms. In turn, these blooms form the basis of a diverse food chain[6].
In winter, the South Atlantic High moves towards the equator, so that the winds reaching the Cape come from the north west and south west, and bring with them cold fronts, rain and storms. The western side of the Cape Peninsula is subjected to large waves, while the eastern side is relatively protected.
As far as animal life is concerned, this means that while the waters on both sides of the peninsula are in general nutrient-rich and support abundant and diverse life, the Atlantic side has lower temperatures and is subjected to much more forceful wave action. False Bay, on the other hand, is a lower energy environment, with more gradual temperature changes, higher temperatures and less severe storm waves. These factors produce the differences in animal life seen on the two sides of the peninsula.
In addition to these dominating impacts on the marine environment, there is also the occasional influence of the warm Agulhas Current, which is formed as a series of eddies in the Mozambique Channel and flows down the east coast. It usually flows offshore of False Bay and the peninsula, but occasionally, under the correct meteorological conditions, eddies of this warm (21-25ºC) water can move into False Bay and past the peninsula bringing with them open ocean visitors such as jellies and whale sharks, and the occasional warm water vagrant.
Marine bioregions edit
The Cape Peninsula is at the meeting point of two continental shelf marine bioregions: the Agulhas bioregion to the east, and the South-western Cape bioregion to the west. This is the most distinct transition zone of all South African marine bioregions, and the difference in the ecology between the two sides of the peninsula is clearly visible.
List of marine animals of the Cape Peninsula and False Bay edit
List of seaweeds of the Cape Peninsula and False Bay edit
Marine geology of the Cape Peninsula and False Bay edit
Conservation edit
Challenges edit
The rich waters around the Cape Peninsula have long been a source of food to the humans living along its shores. Today, with a human population in the millions, and an active export industry, unsustainable demands are being placed on them. Commercial fisheries take out tons of fish and sea life, dragging trawls over delicate reef systems in search of their catch, and discarding unwanted bycatch. International markets for lucrative animals such as abalone, rock lobster and various sought-after species of fish have encouraged less scrupulous and more desperate people in the area to engage in poaching. Recreational anglers and seafood collectors increase the pressure. Efforts to protect ocean life and ensure that the seas are sustainably harvested have been many and varied and have enjoyed differing degrees of success. Commercial fisheries are licensed under a quota system, which is based on scientific estimates of what catch levels are sustainable. The problem of bycatch is a serious one and in some fisheries can be avoided by the use of different techniques or equipment. Recreational fishing and collecting permits are also assessed and issued for sustainability.
Marine Protected Areas edit
Much of the Cape Peninsula was designated a Marine Protected Area (MPA) in 2004. Part of the plan is for no-take zones within this area so that reefs will be left in as pristine a state as possible. These protected areas should allow juvenile marine animals to grow to adulthood and replenish adjacent areas. This strategy has worked well in other parts of the world. Unfortunately illegal efforts in exploiting these waters are unceasing, and authorities are struggling to deal with them. Abalone poaching is particularly serious, and may cause the extinction of the local species within the next two decades. The fight against poachers is a tough one and has many fronts. Firstly there are trawlers which operate illegally in South African waters with seeming impunity. South African territorial waters are large and patrol boats few. Marine and Coastal Management, the government coastal protection arm, has had some success, even using a converted impounded poaching vessel as a patrol vessel, but many illegal vessels go free. Then there is shore-based poaching. Many local communities are poverty-stricken and the money that poaching brings in can mean the difference between survival and starvation for some. Add to that well-equipped poaching syndicates, which are heavily armed, well able to afford fast boats and to pay workers substantially above the going rate, and it is easy to see that countering this problem is unlikely to be straightforward. Marine and Coastal Management is poorly staffed and equipped, so enforcement of regulations is sketchy, and pressure by poachers on community members to turn a blind eye to illegal activities is high.
Conservation organisations edit
erhem. DEAT, WWF, KEAG...
See also edit
- List of echinoderms of South Africa
- List of marine animals of the Cape Peninsula
- List of marine arthropods of South Africa
- List of marine fishes of South Africa
- List of marine mammals of South Africa
- List of marine molluscs of South Africa
- List of seaweeds of South Africa
- Marine geology of the Cape Peninsula and False Bay
References edit
- BRANCH, G., GRIFFITHS, C.G., BRANCH, M. & BECKLEY, L.E. 2005. Two Oceans: a guide to the marine life of southern Africa 2nd edition. ISBN 0-86486-672-0
- DAY, J.H. 1974. A Guide to Marine Life of South African Shores. A.A. Balkema, Cape Town.
- ^ DAY, J.H., FIELD, J.G. and PENRITH, M.J. 1970. The benthic fauna and fishes of False Bay, South Africa. Trans. Roy. Soc. S. Afr. 34(1):1-108.
- ^ GOSLINER, T.M. 1987. Nudibranchs of Southern Africa ISBN 0-930118-13-8
- ^ SAMAAI, T. and GIBBONS, M.J. 2005. Demospongiae taxonomy and biodiversity of the Benguela region on the west coast of South Africa. Afr. Nat. Hist. 1(1):1-96
- ^ MONNIOT, C., MONNIOT, F., GRIFFITHS, C.L. and SCHLEYER, M. 2001. South African ascidians. Ann. S. Afr. Mus. 108(1):1-141
- ^ PAYNE, A.I.L. and CRAWFORD, R.J.M. (eds) 1989. Oceans of Life off Southern Africa ISBN 0-947461-01-9
- ^ BRANCH, G. and BRANCH, M. 1981. The Living Shores of Southern Africa ISBN 9-780869-771150
External links edit
- http://www.panda.org.za/sassi/ for information on sustainably caught fish
- http://www.surg.co.za/ for information on unidentified species
- http://www.uwa.org.za/ for information on MPAs