C O A S TA L A N D M A R I N E L I F E : G E N E R A L
Marine Fossils 3A
Part 1 Precambrian
F
ossils are the remains or traces of dead plants
and animals that have been preserved for
thousands or millions of years. Far from being
How fossils are formed
For something to fossilise it must be buried quickly by sediment
before it decomposes or weathers away. Over time, a shell
dry and boring, the study of fossils has fired the
buried under layers of sand and mud becomes consolidated
imagination and deductive skills of palaeontolo -
into sandstone. New minerals may also gradually replace the
gists and provided valuable insights into ancient
worlds that have been dramatically brought to life
by animated films such as the BBC series ‘Walking
with dinosaurs’. The most common fossils are
shell. Today fossils may be found exposed on cliff faces or
when a quarry or road is excavated. Hard lumps, called
concretions, can form around fossils. When a concretion is
broken open it reveals the fossil, such as a clam. Sometimes
the parts of the creature or plant rot away after being buried,
those of the hard parts of animals and plants such
leaving an imprint in the rock known as a mould fossil. If the
as tree trunks, teeth, bones or shells. For example
hole fills up with rock minerals, it becomes a cast fossil. There
fossilised shark teeth are sometimes found exposed
are some excellent fossil records of early sharks and fish such
on beaches in the Cape and a variety of shells can
as the coelacanth, as well as sea reptiles such as ichthyosaurs
that probably led a life similar to that of dolphins with dozens
be seen in the ancient seabeds that are mined for
of sharp teeth to capture slippery prey. An almost complete
diamonds on the west coast. Only rarely is soft
skeleton of Leptocleidus capensis, a carnivorous marine reptile
tissue fossilised. Sometimes trace fossils such as
with a long neck and flippers was found at Redhouse near
footprints or burrows are preserved. For years the
Port Elizabeth, and reconstructed models can be seen in the
wife of a farmer near Graafwater used a flat stone
museums in Port Elizabeth and Cape Town.
to do her washing, little realising that it bore the
footprints of a giant, two-metre sea scorpion that
Geological time
The geological ages of rocks can be dated by comparing the
stalked the west coast 400 million years ago,
relative amounts of radioactive elements remaining in samples
nabbing primitive fish.
of rock from different strata. Where fossils are found in sedimentary rocky layers the oldest fossils and rocks are in the
bottom layers. Biologists and palaeontologists have shown that
the simplest forms of life occur in the oldest rocks and during
successive geological periods the fossil life has become more
and more complex. Fossil evidence is used to support the
theory of evolution, as it shows changes in the composition
of species through time.
FOSSILS THROUGH THE AGES IN
SOUTH AFRICA
Archaeon period 3500 million years before
present (bp)
Some of the oldest fossil-bearing rocks in the world occur in
the Barberton Mountains in Swaziland. They contain fossils of
simple bacteria, some of them caught in the act of dividing in
two. Column-like layered rocks called stromatolites from the
Barberton group were produced by photosynthetic
Cyanobacteria (blue-green algae), which grew in mats on
ancient ocean floors and trapped fine sedimentary particles.
As the particles cut out the light the mat grew upward to form
a new layer giving the stromatolite its characteristic layered
domed form. These bacteria were the precursors to eukaryotic
A fossil ammonite
organisms that developed some 1400 million years ago and
have cells with a true nucleus. One widely accepted theory is
that the eukaryotes originated when different kinds of bacteria
fused together in a symbiotic relationship. Organelles such as
mitochondria and chloroplasts inside the cells of eukaryotes
Cyclomedusa
probably originated in this way.
Ancient Witwatersrand sea with threads of
gold (up to 2800 million bp)
The Witwatersrand, whose mines have so far produced 45 000
tonnes of gold, was once an ancient sea surrounded by high
granite domes. On the seafloor mats of microorganisms
(algae and bacteria) grew and are believed to have been
responsible for trapping gold and uranium particles, carried
Ernietta
down by rivers. They fossilised as thin but incredibly rich
carbon seams (Carbon Leader Kerogen) embedded with
precious metals.
Pteridinium
Dolomites of the Transvaal supergroup
and iron ore
Rangea
Claudina
Precambrian life in the Nama Sea – soft-bodied
animals left impressions in the sand
The photosynthesis of algae and cyanobacteria in ancient
shallow seas combined carbon dioxide and water to form
from the Nama Vanrynsdorp group present a fascinating
carbohydrates and oxygen. The presence of oxygen in shal-
glimpse at some of the most primitive multi-celled animals
low seas was to change conditions on earth forever. Iron was
and plants as well as puzzling organisms that are difficult to
precipitated out of the water to form layers of red iron ore.
assign to any known group. These were mainly bottom-
Some of the oldest massive banded iron formations in the
dwelling organisms that lived in a shallow marine environment.
world occur in the Northern Cape and the Northern Provinces
They included medusoids (related to jellyfish) and soft-bodied
where iron is mined at Sishen and Thabazimbi respectively.
creatures with a quilted structure. The first hard organisms
The famous red Kalahari and Namibian sands are also rich in
appeared such as calcareous multi-cellular algae while animals
iron. The presence of oxygen also led to the evolution of the
with shells appeared at the end of the Precambrian period.
higher forms of animal life once they could gain extra energy
by aerobic respiration, and the first multicellular organisms
appeared during this period.
The Nama fossils correspond to those in the famous Ediacara
Hills in South Australia with blue-green algae, abundant jellyfish, worms, soft corals and sponges. Tracks and trails on the
Precambrian fossils of the Nama and
Vanrynsdorp (approximately 550-530 million years ago)
seabed indicate that worms burrowed and moved over the
surface. All these creatures were soft-bodied and impressions
of their bodies and burrows were moulded in the sandy bed
The Nama and Vanrynsdorp groups of rocks were deposited
giving the first glimpse of marine life of the Precambrian era.
in a huge basin during the early Cambrian era. This was a
period of major changes in the earth’s history. The tectonic
At the end of the Precambrian period there was a worldwide
plates forming the earth’s surface were actively moving,
mass extinction followed by a 30 million year period when
splitting apart and then some fragments collided to form
many new forms of life appeared very quickly. This explosion
Gondwana. Mountains were built and at least four global
of life occurred in the Cambrian period and is described in
glaciations occurred. The atmosphere of the earth also
the Factsheet: Marine fossils part 2.
changed as photosynthesis increased the oxygen. Fossils
Author: Margo Branch September 2000
FURTHER INFORMATION: • Macrae, C. 1999. Life etched in stone Fossils of South Africa. Geological Society of South Africa, Johannesburg.
RELATED FACTSHEETS: • Ichthyology • Classification of Marine Species • Marine Fossils Part 2
For more information, please contact: The Coastal Management Office, Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2,
Roggebaai 8012, Cape Town, South Africa. Tel: +27 (0)21 402-3208 Fax: +27 (0)21 418-2582 e-mail: czm@mcm.wcape.gov.za Website: http://sacoast.wcape.gov.za
C O A S TA L A N D M A R I N E L I F E : G E N E R A L
Marine Fossils 3A
Part 2 Cambrian to present time
F
ossils are the remains or traces of dead plants
and animals that have been preserved for
and the preservation of fossils. During this period Gondwana
groaned under a huge ice sheet and the South Pole sat on the
thousands or millions of years. The earliest traces
equator in the centre of the future Africa. On the edge of this
of life were simple bacteria occurring 3500 million
ice sheet lay what was to become the Western Cape. The
years before present (bp) that were able to multiply
by division into two. These were the precursors of
South African fossil record of this explosion of life is recorded in
the Cape Super Group strata of the Western Cape mountains
from Cederberg through to Grahamstown.
Eukaryote organisms that have cells with nuclei.
These early forms of life were able to photosynthe -
The Cape Super Group (500 to 300 million years ago)
sise and convert water and carbon dioxide to
The Bokkeveld (530-about 430 years ago) is the interval with
carbohydrates and oxygen. The production of
oxygen changed the environment of the earth for
ever and led to higher forms of life which were able
the richest fossil record within the Cape Super Group. These
are fossils of creatures that were adapted to life in cold seas
and include early examples of all the major invertebrate animal
phyla and a few minor groups. Among them were Trilobites,
to gain added energy by aerobic respiration. During
the precambrian period (550-530 million years ago)
which are the most primitive arthropods with a segmented
simple soft bodied creatures evolved.
compound eyes and a hard exoskeleton. They were once
body in three longitudinal lobes. They had jointed limbs,
very common, with numerous species, but became extinct
250 million years ago.
FOSSILS THROUGH THE AGES IN
SOUTH AFRICA (continued from part 1)
Brachiopods are the most abundant fossils in the Bokkeveld
‘Explosion of life’ in the Cambrian period
food from the water. They are enclosed between two shells
Group. These animals use a comb-like apparatus to filter
At the end of the precambrian period there was a worldwide
mass extinction followed by a 30 million year period when many
new forms of life appeared very quickly. The Burgess Shales in
the Canadian Rockies are one of the most significant marine
fossil beds from this period, and are a rich sample of an animal
and attached by means of a tough stalk. Although they look
superficially like clams, one shell is dorsal and the other
ventral, whereas clams have a shell on either side of the
body. Brachiopods are a totally marine group with only a few
species, the lamp shells, surviving today.
community in the Mid-Cambrian about 530 million years ago.
Gastropod and bivalve molluscs were present – especially
Some of the animals are ancestors of those living today but
burrowing forms.
others are unique and bizarre. Climatic change, increased
oxygen, irradiation and predation are amongst the theories put
forward to explain the sudden appearance of organisms with
hard parts at the beginning of the Cambrian. The shallowing
Echinoderms were rare, apart from the sea lily (a type of
feather star on a stalk), although there are some wellpreserved fossils of brittle stars and starfish.
of the sea and the spread of shallow seas over continental
Fish remains are rare but a well-preserved hagfish was found
platforms provided ideal conditions for the diversification of life
near Clanwilliam, showing even the muscle structure.
Common 500 – 300 million years ago
Brachiopod
Trilobites
The Witteberg Group
(Late Devonian – the ‘Age of the fishes’, 390-345 million
years ago)
The Witteberg Group is later than the Bokkeveld Group and
forms the uppermost unit of the Cape Super Group. While
cutting roads for the Grahamstown southern bypass, an
Ammonites ruled the sea
for 500 million years
extremely significant assemblage of primitive plant and fish
fossils was found. The area, once an ancient lagoon behind
dunes, contains both marine and fresh-water fish fossils,
including the acanthodians (spiny sharks), placoderms
(armoured fish), sarcopterigians (lung fish and coelacanths),
invertebrates. Today the pearly Nautilus is the only surviving
relic of this group.
chondrichthyans (cartilaginous fish such as sharks) and
osteichthyans (the bony fish). Fossilised brown algae similar
In the last 30 years, while prospecting for oil, many fossils of
to Dictyota were found near a metre-long sea scorpion. This
the late Jurassic and Cretaceous periods have been found
collection is now housed in the Albany Museum in Grahamstown.
offshore along the south coast. Microscopic fossils, such as
foraminiferans, diatoms and ostracods are small in size but
Plants and animals invade the land
occur in huge numbers, have a long geological history, a
(Carboniferous, Permian, Triassic and Jurassic periods
rapid rate of evolution and distinct patterning of their shells.
345-136 million years ago)
Because the many individual species each lived for a short time
The accumulation of the Cape Super Group strata ended
with the 50 million year long Dwyka Ice Age which caused
much extinction. After this ice age a wide variety of land
plants and animals evolved. An amazing variety of entrapped
span, they are ideal tools for dating and correlating strata and
have proved invaluable in the search for oil and locating the
natural gas fields off Mossel Bay.
Langebaanweg 5 million years ago
fossils occur in the Karoo Basin, which is famous for its
dinosaur and mammal-like reptile remains.
Algoa Bay
(late Jurassic and Cretaceous period about 150–65 million
years ago)
During phosphate mining at Langebaanweg many fossils were
unearthed. These contained the remains of mammals, many
now extinct, such as a bear, sabre-tooth cats, short-necked
giraffes and three-toed horses. There were also numerous
fishes including a megatooth shark and the remains of seals
Whilst dinosaurs dominated the continents during the mesozoic
and penguins. At nearby Elandsfontein, a clearly more recent
era 230–65 million years ago, the oceans were teeming with
site, the fossilised bones of an early man ‘Saldanha man’
a variety of marine life including dolphin-like ichthyosaurs and
believed to be between 400 and 700 thousand years old,
jet-propelled ammonites. About 20 types of ammonites have
were unearthed. The history of early man along the shore is
been found in the Algoa Basin and the Sundays River area
told in the factsheet ‘Strandlopers and Shell Middens’.
near Port Elizabeth. Superb examples of ammonites occur
Author: Margo Branch September 2000
around Richards Bay and some can be seen at a site on Lake
St Lucia. Ammonites were squid-like creatures housed in
straight or coiled shells. The shells were divided into compartments with air chambers to allow them to lift off the seabed
and swim. Ammonites and related nautiloids ruled the open
seas for over 500 million years, reaching dramatic sizes for
A plesiosaur, a marine reptile
FURTHER INFORMATION: • Macrae, C. 1999. Life etched in stone Fossils of South Africa. Geological Society of South Africa, Johannesburg.
• Walking with Dinosaurs. BBC Discovery series, book and video
• Gore, R. 1993. Explosion of Life: the Cambrian period. 1993. National Geographic. Vol 184 (4) p120-135
RELATED FACTSHEETS: • Marine Fossils Part 1 • Coelacanth • Mining the Sea • Langebaan Lagoon • Strandlopers and Shell Middens • St Lucia
For more information, please contact: The Coastal Management Office, Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2,
Roggebaai 8012, Cape Town, South Africa. Tel: +27 (0)21 402-3208 Fax: +27 (0)21 418-2582 e-mail: czm@mcm.wcape.gov.za Website: http://sacoast.wcape.gov.za
C O A S TA L A N D M A R I N E L I F E : G E N E R A L
Plankton 3A
P
lankton is a collective term used for all
small aquatic organisms that are suspended
in the water column, including both plants
(phytoplankton) and animals (zooplankton). In
the marine environment, planktonic organisms
drift at the mercy of ocean currents.
Phytoplankton cells also need nutrients to survive, especially
nitrogen in the form of nitrate. They are therefore more
abundant in shallow coastal areas than in the oligotrophic
(nutrient-poor) waters of the open ocean, and reach highest
concentrations in upwelling areas. On South Africa’s west
coast, for example, strong south-easterly winds during spring
and summer drive the upwelling of cold, nutrient-rich bottom
water to the surface. The nutrients enhance the growth and
multiplication of diatoms, forming dense “blooms” that
Phytoplankton
provide abundant food for zooplankton and small fish. As
Phytoplankton is the microscopic ‘plant’ life that is able to
produce organic compounds from water and carbon dioxide
a result, the west coast is South Africa’s most productive
fishing ground.
by photosynthesis, and forms the basis of the marine food
Between upwelling events the sea becomes calmer and warmer,
chain. Since light is necessary for photosynthesis, phyto-
and these conditions are more suitable for the development
plankton cells must stay in the upper layers of the ocean rather
of phytoplankton blooms dominated by dinoflagellates. These
than sinking down into the dark depths. Many form long
blooms can become so dense that they discolor the water
chains as they divide and multiply, which helps reduce their
various shades of red, orange, brown or purple because of
sinking rate by increasing their surface area. Some, called
pigments within the cells. Some of these so-called “red tides”
diatoms, have long spines and oil droplets to take advantage
are made up of toxic dinoflagellate species. Filter-feeding
of turbulence in the water and to provide buoyancy. Others,
organisms such as mussels and oysters accumulate the toxins
the phytoflagellates and dinoflagellates, have whip-like
in their tissues, and when eaten by humans cause various
appendages called flagella that beat for weak locomotion.
types of shellfish poisoning.
Eutreptiella sp.
Thalassiosira
decipiens
Nitzschia
closterium
Rhizosolenia
hebetata
Cerafium
hirudinella
Melosira sp.
Chaetoceros
decipiens
Cocconeis sp.
Dinoflagellates
Zooplankton
Zooplankton feed either on phytoplankton or on smaller
zooplankton. They can be conveniently divided into three
size classes:
• microzooplankton, incorporating animals in the size range
2-200 µm (micrometres)
• mesozooplankton of 200-2000 µm (2 mm) size
• macrozooplankton, including those animals larger than
2 mm that cannot resist transport by currents.
Navicula sp.
Diatoms
heterotrophic dinoflagellates, foraminiferans and radiolarians. The
ciliates are the largest group and have numerous short cilia for
locomotion and suspension feeding. Ciliates smaller than 30 µm
are the most important microzooplanktonic consumers in the
sea. Some ciliates and dinoflagellates do not have a rigid outer
layer and are capable of adjusting their body shape to ingest
cells their own size or even larger. Foraminiferans construct
intricate calcareous shells, which over the centuries have formed
vast deposits on the ocean floor, as the animals sink after
dying. One of the more spectacular examples of this type of
deposit is the White Cliffs of Dover on the south-east coast of
Microzooplankton is dominated by protozoans, which are
England. These chalk cliffs were formed millions of years ago
tiny single-celled animals. They include zooflagellates, ciliates,
when the sea level was much higher than it is today.
Mysid larva
Medusa
Phyllosoma
larva of rock
lobster
Doliolum
Muggiaea
Zoea larva
of crab
Copepod
Arrow worm
Arrow
worm
Juvenile fish
Megalopa
larva of crab
Egg
Polychaete
worm larva
Mesozooplankton is dominated by crustaceans, which belong
shimmering shards of glass in the water as they swim. They
to the phylum Arthropoda. Copepods are the most abundant
are voracious carnivores with powerful jaws, and are capable
mesozooplankton, representing 60-80% of the total biomass
of consuming juvenile fish their own size. Macrozooplankton
of zooplankton in the oceans. They are an essential link in the
also includes jellyfish, ctenophores (comb jellies) and jelly-like
food chain, as they filter-feed phytoplankton from the water
tunicates (salps, doliolids and appendicularians).
and are in turn consumed by macrozooplankton, fish and
baleen whales. Other crustaceans are the cladocerans (water
fleas), easily recognized by their single, large compound eye,
and the ostracods (mussel or seed shrimps), which have a
bivalve shell. The larvae of cirripedes (barnacles) are also
common crustaceans in the mesozooplankton size class.
Macrozooplankton is made up primarily of larger crustaceans
of the class Malacostraca. Included here are euphausids,
shrimps, prawns, amphipods and mysids (opossum shrimps),
as well as the planktonic larvae of rock lobster and crabs.
The largest euphausids are the 6-cm “krill” that occur in the
Antarctic, where they form huge swarms extending over
many kilometres. Krill are the main food source of many filterfeeding baleen whales, which spend summer and autumn
feeding in the Antarctic.
An important component of zooplankton is the icthyoplankton,
comprising the eggs and larvae of fish species. Fish release
large numbers of eggs into the water, and many of these hatch
into larvae. However, natural mortality and predation of both
eggs and larvae is extremely high, so only a small percentage
survive to adulthood.
Survival strategies Zooplankton exhibit a variety of predator
avoidance strategies. Many species undertake daily vertical
migrations, congregating near the surface at night to feed and
then sinking back to the deeper layers during the day, although
this may just be to conserve energy rather than to escape
detection by predators. Others are camouflaged by being
transparent or by merging into the background colour.
Euphausids have small light-producing organs called photophores on various parts of the body, which emit a bright flash if
Other common members of the macrozooplankton are the
the animal is attacked or chased. This confuses the predator,
chaetognaths, which reach a length of 10 cm in some species.
providing an opportunity for the euphausid to escape.
They are commonly called arrow worms owing to their shape,
or glass worms because they are transparent and resemble
Author: Sue Matthews September 2000
FURTHER INFORMATION: • Branch, G. & Branch, M. 1981. The Living Shores of Southern Africa . Struik Publishers, Cape Town.
• Payne, A.I.L., Crawford, R.J.M. & Van Dalsen, A. 1989. Oceans of Life off Southern Africa . Vlaeberg Publishers, Cape Town.
RELATED FACTSHEETS: • Upwelling • Red Tides • Krill • Crustaceans • Baleen and Toothed Whales • Whaleshark • Classification of Marine Species
For more information, please contact: The Coastal Management Office, Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2,
Roggebaai 8012, Cape Town, South Africa. Tel: +27 (0)21 402-3208 Fax: +27 (0)21 418-2582 e-mail: czm@mcm.wcape.gov.za Website: http://sacoast.wcape.gov.za
C O A S TA L A N D M A R I N E L I F E : G E N E R A L
Dangerous Sea Creatures 3A
D
angerous creatures of the sea can generally
Spearfishers are most at risk of being attacked because
be divided into those that inflict injuries to
sharks may be attracted by the blood of the speared fish. It is
humans by biting, by being venomous or by being
advisable for spearfishers to trail their catch behind them on a
poisonous. Venomous creatures are those that use
long rope. Other tips to minimise the risk of shark attack are
to avoid swimming near seal colonies or shoaling fish (as
spines, teeth or stinging cells to inject a painful or
occurs during the sardine run), in murky water, and near
dangerous substance, called venom, into a wound.
deep-water channels or the edge of a sandbank (where
Poisonous creatures are those that cause pain,
sharks patrol for prey).
illness or death when eaten.
The moray eel is another marine creature that sometimes
injures people by biting them. On the east coast, two species
belonging to the genus Gymnothorax – the honeycomb (or
Biting creatures
reticulated) and yellow-edged (or leopard) moray – share
crevices and dark holes in the reef with crayfish. These morays
Sharks are without doubt the most feared creatures in the
have large, powerful jaws with sharp teeth, and have been
sea, with a reputation for being ferocious man-eaters.
known to bite divers’ hands as they reach in for crayfish.
However, most species of shark are perfectly harmless, and
feed mainly on fish, octopus or even small crustaceans on
the seafloor, while the largest of all sharks – the whale shark –
filter-feeds on plankton.
Venomous creatures
The stonefish Synanceia verrucosa, is the most venomous fish
in existence. It occurs widely in the tropics and in South African
A number of sharks in South African waters are potentially
waters north of Durban. This fish is a drab, mottled brown and
dangerous, but the two associated with the most attacks are
has a rough, warty skin, imparting excellent camouflage as it
the Zambezi shark and the great white shark, both widely
rests on rocky or coral reefs or on the sandy seafloor. Along
distributed in the world’s temperate and sub-topical oceans.
its back is a row of hollow spines, each with its own venom
The Zambezi shark, Carcharhinus leucas, occurs along the
sac. If a person accidentally treads on the stonefish, the spines
east coast of South Africa, where it is found in inshore waters,
pierce the victim’s skin and inject venom, resulting in an
river mouths and estuaries. The great white shark, Carcharodon
extremely painful injury that may be fatal if not treated quickly.
carcharias, is more common along the south and west
coasts, particularly around seal colonies, which provide a
readily available source of food. It also occurs close inshore,
bringing it into close proximity to bathers, surfers and divers.
A small number of shark attacks occur each year, but few are
Firefish are related to the stonefish and scorpionfish in the
family Scorpaenidae. There are several species of firefish,
which belong to the genus Pterois. These beautiful fish ar e
also known as zebrafish, devilfish and lionfish. They are a reddish-brown colour with white bars, and have a ‘mane’ of long
deadly. In most cases the shark leaves the victim after an
dorsal spines and pectoral fin-rays that sway as the fish
initial exploratory bite, indicating that the attack is a case of
swims. When needed for defence, however, the dorsal spines
mistaken identity or curiosity. However, even these victims
can be held rigid and stabbed into the enemy to inject a
may die of shock and blood loss if not treated rapidly.
powerful venom.
venomous spines
venomous spines
Stonefish
Firefish
Other fish that stab offenders with spines to inject a venom
Puffer fish
Poisonous animals
are spiny dogsharks, stingrays, elephantfish,
Puffer fish or blaasops, include several
catfish, rabbitfish and surgeonfish.
species in the family Tetraodontidae
Cone shells, belonging to the
and can be recognised by their ability
genus Conus, are the most
to inflate themselves by swallowing air
dangerous of the molluscs. These sea snails have scores of
or water as a defence strategy when
tiny ‘poison arrow’ teeth that are stabbed or shot into prey to
threatened. The flesh of these fish contains a
inject a venom, which paralyses the prey. The venom of most
powerful neurotoxin that is extremely poisonous. An initial
species is only mildly painful or irritating to humans, but is
tingling of the lips and tongue is followed by numbness
potentially lethal in some tropical species.
throughout the body and ultimately respiratory paralysis,
Other invertebrates, such as certain sea urchins, starfish
and polychaetes (bristleworms), also have spines or bristles
resulting in death. Urgent hospitilisation should be sought if
these fish are eaten.
that inject a venom, causing a stinging sensation. The
Shellfish poisoning in humans is usually the result of eating
cnidarians, which include jellyfish, bluebottles and firecoral,
mussels or oysters contaminated with poisonous red tides
inject venom using cells called nematocysts – these stings
(various types of planktonic organisms that cause toxic algal
can be relieved with meat tenderiser or vinegar.
blooms). If rock lobsters eat these mussels, the toxins end up
Treatment for venoms
(brown meat) of rock lobster should therefore not be eaten,
in the digestive glands of the rock lobster. The digestive gland
the white meat is not poisonous.
In all cases, the most effective treatment for venom is
immersion of the wound in water as hot as can be borne.
The livers of many fish , including some sharks and the red
This destroys the protein-based venom and relieves the pain.
steenbras, Petrus rupestris, contain very high concentrations
of vitamin A, which is toxic to humans.
Medical advice should be sought to prevent secondary
infection, or if there is a risk of respiratory or
Other dangerous creatures
cardiac failure.
Some dangerous creatures in the sea do not
The yellow-bellied seasnake, Pelamis platurus,
fall into any of the above categories.
is a venomous reptile that occurs throughout the
Electric rays, for example, are disc-shaped fish
Indian and Pacific Oceans. It usually remains far
offshore, some individuals however, get caught in the
belonging to the genus Torpedo, that have electric
Agulhas Current and swept into the colder waters of
organs capable of generating powerful shocks, which are
used for stunning prey and for defence. Electric rays tend
the southern Cape, where they may become stranded
to bury themselves under a layer of sand and are so well
on the shore. These snakes, which can be easily
recognised by their bold yellow and black
camouflaged that humans sometimes tread on them acci-
coloration and flattened tail section, should
dentally, and are given a startling jolt.
be given a wide berth or handled only with
Electric
ray
Razor clams: The razor-sharp edges of the horse mussel’s
extreme care, even if they appear to be dead.
shell, which protrudes from the sand, often causes wounds
Although they have quite small fangs and are not aggressive,
when trodden on. As a result this species, Atrina squamifera,
their bite is extremely venomous. The venom acts by
as well as the related Pinna muricata, are also known as
paralysing the muscles, and may cause spasms, convulsions,
razor clams.
respiratory distress and unconsciousness. Bite victims should
therefore seek medical attention immediately.
Author: Sue Matthews October 2000
FURTHER INFORMATION: • Smith, MM 197-? Sea and shore dangers . JLB Smith Institute of Ichthyology, Rhodes University, Grahamstown.
• Van der Elst, R 1990 A guide to the common sea fishes of southern Africa. Struik Publishers, Cape Town.
RELATED FACTSHEETS: • Sharks • Stingers – Bluebottles and Jellyfish • Red tides • Skates and Rays • Eels • Sea Urchins • Sea Shells
For more information, please contact: The Coastal Management Office, Marine and Coastal Management, Department of Environmental Affairs and Tourism, Private Bag X2,
Roggebaai 8012, Cape Town, South Africa. Tel: +27 (0)21 402-3208 Fax: +27 (0)21 418-2582 e-mail: czm@mcm.wcape.gov.za Website: http://sacoast.wcape.gov.za