The rocky shore is one of the most
fascinating of all ecosystems. It is packed with a
wide variety of marine life. The shore is covered by
the sea and pounded by the waves at high tide in the
intertidal zone. Low tide means exposure to drying
air and heat. Plants and animals living here must be
able to live both in air and water; they must be able
to survive the loss of almost 70 % of their body
water during dry periods, and, in addition, be able
to cope with freshwater rain when exposed and salty
seawater when submerged.
FIXED AND MOBILE ANIMALS
* Mobile animals: are very active and move
up and down with the tides. They can retreat into
gulleys and under rocks when conditions become
stressful. They include the crabs, small fishes, sea
lice, star fishes and many of the sea snails. Mobile
animals are often well camouflaged which helps them
escape predation or to surprise prey. Others like the
sea slugs are brightly coloured to advertise that
they are poisonous and so warn off hungry predators.
* Fixed or sedentary animals:
such as barnacles or mussels survive best in a narrow
range of conditions to which they are adapted. Some
are thus confined to the high shore while others are
found only at low tide level. They spend their lives
firmly attached to the rocks so that they cannot be
washed away by the waves. They are usually protected
by shells which can be sealed shut during the dry
period to reduce water loss. As they cannot move in
search of food they rely on the filtration of small
particles of food from the water that washes over
them at high tide.
Mussels circulate water through
their shells, barnacles use their feathery limbs to
comb particles from the water and many tube worms
have tentacles to collect food particles. The
beautiful sea anemones capture small creatures that
stray within range of their tentacles. Sedentary
animals are easy prey for birds, fish, crabs and
octopuses and this is why they have developed various
methods of defence such as thick protective shells.
South African shores are famous for their limpets.
There are 13 species, each occurring in a particular
zone on the shore. The limpets roam the rocks
scraping off algal spores and young seaweeds with
their rasp-like tongues. Each limpet has a home scar
on the rock to which its shell has grown for an exact
fit. It returns to this spot at low tide and clamps
firmly to the rock, providing itself with protection
from wave action and water loss as well as making it
difficult for capture by predators. Some species of
limpets do not move far from their home scars and
cultivate and protect a private garden of seaweeds
around them. By nibbling only the tips of the
seaweeds, like cutting a lawn, they maintain a
constant supply of food. The pear limpet is so
successful that it can survive at densities of 2 600
per square metre. On the south and west coasts, it
forms a dense band at the low tide level.
THREATS TO ROCKY SHORES
Rocky shores and the life associated with them are
harmed by pollution, much of which is brought to the
coast by rivers. Sewage in river water can carry
cholera which is then taken up by shellfish and, when
this is eaten by people, the latter can become
infected. Many rocky shores are subject to
indiscriminate collecting of bait, shells and rock
WHAT YOU CAN DO
* Visit the rocky shore at low spring tide. Walk from
the high water mark on a rock platform down the
shore, noting how the animals and seaweeds occur in
* Do not buy sea shore curios
unless you are sure they are legally collected and
are not a threatened species.
* Do not remove sea shore life
unnecessarily or without a licence if one is
THE LIVING SHORES OF
SOUTHERN AFRICA. G. and M. Branch. Struik,
M. Branch. Struik, 1987.
HANDS ON THE EAST COAST
ROCKY SHORES: A FIELD GUIDE. T. Stewart.
1991. Share-Net, P O Box 394, Howick, 3290.
A FIELD GUIDE TO THE
EASTERN CAPE COAST. R. Lubke, F. Gess and M.
Bruton (eds). Wildlife Society, Grahamstown, 1988.
EAST COAST IDENTIFICATION
GUIDE. Posters, available from Treasure
Beach Project, PO Box 16126, Brighton Beach, 4009.
and R. Griffiths. Struik, Cape Town, 1988.
All books available from Russel
Friedman Books, PO Box 73, Halfway House, 1685. Tel.
Institute. P O Box 10712, Marine Parade,
4056. Tel. 031-373536.
Treasure Beach Project.
PO Box 16126, Brighton Beach, 4009. Tel. 031-478507.
East London Museum.
Upper Oxford Street, East London, 5200. Tel.
Somerset Street, Grahamstown, 6140. Tel. 0461-22243
Port Elizabeth Museum.
Beach Road, Humewood, Port Elizabeth, 6001. Tel.
The South African Museum.
Marine Biology Department, Queen Victoria Street,
Cape Town, 8001. Tel. 021-243330.