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The east coast
waters are characterised by the warm waters of the
southward flowing Agulhas Current, while those of
the west coast are characterised by the upwelling of
cold, nutrient-rich waters of the Benguela Current.
Along the southwest and south coast, there is an
extensive mixing of water masses. The currents
influence the composition of the animal and plant
communities along this coastline.
Sandy beaches consist of an unstable sandy
bottom layer that is continually modified by waves
and currents, resulting in an absence of plants
between the tide marks. Yet, a few animal species
have adapted to live in this harsh environment.
For
example, the plough snail (Bullia sp.) and white
mussel (Donax sp.) have adapted by burrowing in the
sand. These animals emerge to feed when conditions
are relatively mild, or they sit tight in the sand
and filter food particles from the seawater with
siphons or strainers.
The pink ghost crab (Ocypode
ryderi) burrows deeply by day, emerging by night to
feed on deposited carrion and small animals. Other
animals, such as the leatherback turtle (Dermochelys
coriacea), merely visit the intertidal zone to lay
their eggs.
The rocky shores that are scattered along the
coastline provide a firm foundation for the
attachment of plants and animals, but are exposed
twice a day by the tides and are often lashed by a
strong wave action.
These shores support a great
diversity of marine organisms, some of which are
commercially significant, for example, mussels,
oysters and seaweed.
The intertidal and the subtidal
zones provide feeding grounds for many species of
fish, some of which are important angling species.
South Africa’s only coral reefs occur in
the subtropical waters off the coast of
northern
KwaZulu-Natal and Maputaland. These
particularly fragile environments support an
abundant growth of Indian Ocean corals that
harbour diverse Indo-Pacific fish fauna.
These reefs form a vital link in the overall
food web of southeast Africa and play an
important role in the distribution of
migratory fish.
Commercially important
species such as the larger mackerels, couta
and kingfishes migrate along the narrow belt
of the coral reefs of Maputaland, to reach
southern African waters during the summer
months.
Lekker Links
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The west coast is dominated by dense
beds of the giant kelps or sea bamboo (such
as Ecklonia maxima), which form a calm
underwater forest-like habitat and can
extend to as much as 3 km offshore. These
kelps are extremely productive. Not only are
they a major source of food, but they also
provide shelter for fish, animals and plants
that inhabit calm waters such as the
commercially important rock lobster and
abalone stocks.
In the open sea, there is no firm base,
and organisms must either drift or be able
to swim. Examples include the bottlenose
dolphin (Tursiops truncatus), the
blue-and-gold fusillier (Caesio caerulaureus),
the Cape moony (Monodactylus falciformis)
and the Japanese bigeye (Pristigenys
niphonia), phytoplankton and zooplankton.
The east coast waters are characterised
by a greater biotic diversity than the
southwest and south coast waters where fewer
species occur but in greater numbers. The
main focus of commercial fisheries is
therefore centered in the more productive
waters of the southwest and south coasts.
The cold tidal waters close to the south
and eastern coast of South Africa make
sharks a common occurrence. Divers come from
around the world to South Africa to dive
with sharks, such as the ragged tooth shark,
Carcharias Ttaurus (or “raggies” as they are
locally known).
Despite their large size and fearsome
rows of sharp teeth, raggies are docile and
allow divers to approach within a few
metres. In winter and spring, ragged tooth
sharks can be readily seen on the Aliwal
Shoal – a submerged reef on the east coast
of South Africa, 50 kilometres south of
Durban.
Mothers give birth to two live young
which spend their first few years in the
waters of the Eastern Cape. When they’re old
enough, the youngsters join the adults on
the annual migration up the east coast to
northern
KwaZulu-Natal and southern
Mozambique. On the way, they spend some time
at offshore reefs such as the Aliwal Shoal,
where they may engage in courtship and
mating.
(Source: South Africa
Department of Environmental Affairs and
Tourism and WWF)
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