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Best of both worlds:
the two oceans of South Africa
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.
S
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
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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 biogeographic 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’.”
Different worlds
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.
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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.
coast are usually silver or yellowbrown. 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
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.
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.
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.
“Schools of fish migrate
northwards followed by predators
including elf, yellowtail, Garrick
and mackerel. Various shark
species also join the hunt.”
Unlike their rainbow cousins on
the east coast, the fish on the west
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
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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.
Biodiversity
· Biodiversity is defined as “the
variety of plant and animal life
in the world or in a particular
habitat, a high level of which
is usually considered to be
important and desirable”.
· 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.
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