The Atlantic and Indian oceans mix and mingle off South Africa’s coast, producing a bounty of fascinating flora and fauna both on land and in the water. Writer Ingrid Sinclair takes us on a tour.
Text: Ingrid Sinclair Country: South Africa
outh Africa has a natural landscape that is as diverse as its people. On land, it is considered one of the most biologically diverse places on earth. But look a bit further and you’ll find that South Africa also has one of the world’s most interesting coastlines. The coastline often defies clear definition, and it boasts the best of two worlds.
Two ocean currents — one warm and one cold — sweep past the subcontinent, changing the appearance and behaviour of the plants and animals that live in these waters. The huge variations and complexities of South African marine fauna and flora make for an unpredictable environment. Whales, dolphins, seals, sharks, plants, fish and birds — you name it; the South African coast has it.
One nation, two oceans
The two currents that meet at the southern tip of Africa are the cold Benguela current of the west, flowing through the Atlantic Ocean, and the warm Agulhas current of the east, which flows through the Indian Ocean. Only 20 other countries of the world’s roughly 196 nations can claim two or more oceans or seas on their borders. But even fewer of these countries’ seas are this radically different in terms of the life they host.
“Due to the influence of the currents, as well as the country’s latitude, South Africa experiences tremendous changes in weather and climate,” says Helen Lockhart, Cape Town’s Two Oceans Aquarium communications and sustainability manager. For example, Port Nolloth on the west coast sees an average annual temperature of 14.1°C and an annual rainfall of 61mm. Durban on the east coast, which lies on the same latitude as Port Nolloth but on the opposite coast, experiences average temperatures of 20.5°C and receives 1,000mm of rain every year.
Finding the middle ground
Where the Indian and Atlantic oceans actually meet has always been the topic of many heated arguments among South Africans. Even marine biologists seem to be divided on the issue, and that is because of the flowing nature of water.
“If there is such a thing [as a meeting point of the two oceans],” says Lockhart, “the boundary lies somewhere between Cape Agulhas (the southernmost tip of Africa) and Cape Point. Based on the differences in plant and animal life occurring north-west and south-east of Cape Point, some people like to believe that Cape Point is the dividing line.”
This so-called dividing line is a major tourist attraction. Cape Point, just an hour’s drive from Cape Town, attracts around 800,000 foreign and local tourists every year. They come to marvel at the stunning cliffs, lighthouses and, of course, animals that populate the area. So popular is the idea of the two oceans that South Africa has a premium wine brand and an extremely successful marathon named after it.
But any physical definition of a meeting point or dividing line between two oceans ignores the fact that currents don’t just halt their flow at any point. According to leading South African marine scientist, Professor George Branch, co-author of Two Oceans: A guide to marine life of southern Africa, “There is much more interest in asking where plants and animals change in composition and functioning from one bio-geographic region to another. Inshore, there is no doubt that the biggest divide is at Cape Point. As one moves offshore, the biotic division swings eastwards.
“Ocean currents don’t meet at a fixed point. They shift and mingle. I am still most comfortable believing what the biota tells us: the biggest bio-geographic divide on the coast (and one of the most obvious in the entire world) is at Cape Point. In stating this, I’m not arguing for geographers to redefine oceans or for Cape Agulhas to give up its indisputable case for being at the juncture of the oceans. I’m simply pointing out the biological arbitrariness of the dividing line, which doesn’t coincide any obvious divisions of biological composition or processes.
In terms of where currents meet (as opposed to oceans), Cape Point is the place I’m most comfortable with saying that that’s where the Agulhas and Benguela currents meet along the shore. But currents shift, and portions of the waters from the Agulhas find their way right around the globe on the ‘global conveyer belt’.”
The Agulhas current moves warm Indian Ocean water from tropical regions down the east coast of South Africa.“The region stretching from southern Mozambique to Port St Johns is referred to as subtropical. It supports tropical species of corals, fishes and crabs, and also various temperate species from southern latitudes,” says Lockhart.
There are more predators here than on the west coast, but there are relatively fewer nutrients in the warmer water, so marine species are always competing for food. This explains why there are more poisonous and venomous animals on the east coast, including stonefish, devil firefish and various species of sea urchins, than on the west coast.
And while there are more species of marine animals on the east coast, there are fewer of them than on the west coast.
The east coast’s waters are lit up with a range of very colourful fish like butterfly fish, wrasse, damsels, goldies and surgeonfish. Colourful fish are generally more common in tropical waters around the world.
On the east the warm currents flow south, but off the west coast of South Africa the cold Benguela current is headed north. This region’s cold waters host species that are predominantly endemic and occur in high numbers. For this reason, the fishing of abalone and west coast rock lobster is a big contributor to the South African economy.
South Africa’s west coast is one of the richest fishing grounds in the world. Apart from supporting the massive commercial fishing industry, the west coast is also home to big populations of Cape fur seals and seabirds like African penguins.
The galjoen, which lives on the west coast, is South Africa’s national fish. It is found nowhere else in the world. Unfortunately, overfishing has affected galjoen populations negatively. Commercial fisheries cannot catch and sell it, and recreational fishers may only catch two galjoen (bigger than 35 cm) per day, and only between March 1 and October 14 each year.
Unlike their rainbow cousins on the east coast, the fish on the west coast are usually silver or yellow-brown. Some west coast species, like red roman, sport a deep red colour, but because they live in deeper waters, the red colour fades because there is less light at that depth.
Another remarkable characteristic of the west coast is its kelp forests. These marine plants prefer the nutrient-rich cold water and are the perfect habitat for seals and penguins. Kelp is a large species of seaweed and it acts as a water purifier, feeding on fish waste products like ammonia. Modern-day uses of kelp include agricultural growth stimulant, erosion prevention for waterproofing and as a health stimulant.
Mixing it up in the south
Between the west and the east coasts of South Africa, there is another significant coastal region called the south coast. This is what’s known as a mixing zone, says Lockhart. “Many fish tend to migrate through this region during winter.
During this winter-time migration, giant schools of pilchards travel up the east coast of South Africa. Known locally as the Natal sardine run, marine animals like seagulls and dolphins cash in on nature’s jackpot by following the shining shoals and feeding to their heart’s delight. It is truly a spectacular sight as the east coast becomes overrun by masses of silvery fish and their predators.
During these months, southern right whales also visit the Cape south coast. The whales mate and give birth close to shore, resulting in one of the most spectacular land-based whale-watching opportunities in the world.
A visit to South Africa is therefore truly an exercise in witnessing the best of biodiversity that the world has to offer. More than 11 ethnic groups makes for a diverse and interesting human population; the famous Big Five on land – elephant, leopard, rhino, buffalo and lion – make safaris a wondrous affair; and the two oceans of the country provide thousands of kilometres of ocean-inspired awe.
· With a land surface area of 1.1 million square kilometres — representing just 1% of the earth’s total land surface — South Africa contains almost 10% of the world’s total known bird, fish and plant species, and over 6% of the world’s mammal and reptile species.
· South Africa is home to about 15% of the world’s marine invertebrates, and about 16% of the country’s marine fish are found nowhere else in the world.