Factsheet 1. Rocky Shoreline Ecology
What is a Rocky Shoreline?
The Splash Zone:
Rocky shores form in coastal, intertidal regions between
the extreme high and low tide marks. They can range from
steep, inaccessible cliffs to wide, gently sloping platforms
or extensive boulder beaches. The plants and animals
that live in these environments have to be able to survive
the extreme conditions that occur. This includes being
pummelled by waves, being inundated with seawater then
dried out on every tide, as well as significant temperature
and salinity extremes. As if this weren’t enough, they can
also be eaten by land animals, like birds, when the tide is
out, and sea animals, like fish, when the tide is in. Even
though conditions in these environments are harsh, rocky
shorelines support a wealth of biodiversity.
This is the area above the high tide level, wetted only by
spray. In areas with rough seas and steep cliffs, the splash
zone may extend to a considerable height, whereas in
calm regions the splash zone may not even exist.
Organisms commonly found in the splash zone include
periwinkles and crabs.
How are they formed?
The main force acting on coastal areas is wave action, and
this shapes platforms, cliffs and boulders over time. This
shape depends on the underlying geology. Soft rocks such
as sandstone are worn away relatively easily by the
erosive action of waves, whereas harder rocks such as
basalt and granite do not erode so readily. This creates a
diverse and complex physical environment with many
habitat niches that plants and animals can occupy.
Zonation
The splash zone is much larger on this cliff face, left, than on this
flatter shoreline, right.
The Tidal Zone
This is the area that is covered and uncovered by the tide
twice a day, and is commonly broken down into three
smaller zones – the high tide, mid tide, and low tide zones.
Creatures that can be found across these areas include
chitons, limpets, top shells, nerites and mulberry whelks.
Further down the tide line bands of animals less tolerant of
dessication, such as cunjevoi, tube worms and sponges,
start to appear.
The Low Shore Fringe
If you look closely at a rocky shoreline, you will start to see
that many organisms form in characteristic bands across
the landscape. This is called zonation, and it occurs as a
result of the different physical conditions found in these
environments The main zones on rocky shorelines are the
splash zone, the tidal zone, and the low shore fringe. .
Whereabouts on the tideline an organism occurs depends
largely on its ability to tolerate dessication and/or wave
action. For further information on the shells, plants, and
animals of rocky shorelines refer to factsheets 2-5 of this
series.
This is where the waves are breaking when the tide is at
its lowest. Most marine plants can be found in abundance
in this region.
The low shore fringe is where the waves are breaking at low tide.
WetlandCare Australia: Supporting the community to protect and restore Australian wetlands since 1991
Adaptations
Filter feeders:
Living in this harsh environment requires many of the
animals to have special adaptations that protect them
against environmental extremes such as large
temperature ranges or tidal fluctuations. Many shellfish,
for example, have a special type of ‘door’ (called an
operculum) that they can close tightly to protect them
from drying out when the tide is low. Others secrete a
mucousy substance around their shell that forms an
effective seal against moisture loss. Others, such as sea
anemones and cunjevoi are able to retain water inside
their bodies until the next tide.
Animals such as sponges, cunjevoi, tube worms and
barnacles filter out plankton and other small particles from
the water. Because they are filter feeders, these
organisms are only able to access food when they are
covered with water and because of that most of them,
particularly the larger ones, are usually found lower down
the tidal zone.
Detritus feeders:
Most detritus feeders (or detritivores) are crabs, which can
often be seen shovelling sand particles into their mouths,
where they separate out the detrital material that has
formed a layer over the sand. Crabs are also scavengers.
Hunters:
Rocky shorelines are dynamic and challenging places to live.
Organisms that are able to thrive in these conditions have
special adaptations to help them deal with environmental
extremes.
Feeding
Being such a complex habitat, there are a vast array of
interactions that take place between the organisms that
inhabit rocky shorelines. Here are some of the different
types of feeding behaviours used by animals in these
environments.
These animals are carnivores, and have a variety of
interesting ways to eat their prey. Whelks, which are a type
of marine snail, have a specialised tube called a siphon
which picks up chemical signals from their prey. Once they
have located their prey using their siphon, they then bore a
hole through its shell and eat it. Sea stars actually shoot
their stomach out through their mouth and partially digest
their food before sucking it back into their body. Others,
like sea anemones, just wait for prey to drop into their
arms where they trap it and eat it.
Did you know?
Sponges are actually animals although
they don’t have organs like other animals.
They draw water in through small pores in
their body and then filter out food particles
from the water column.
Grazers:
Other factsheets in this series are:
Animals such as limpets, chitons and many of the marine
snails use their radula to graze on microalgae. A radula is
a long organ that contains numerous tiny teeth that
scrape the thin film of algae off the rocks. Larger animals,
such as sea urchins, use hard plates located in their
mouths to scrape the rock surface.
2. Shells of Rocky Shorelines
3. Birds of Rocky Shorelines
4. Rock Pool Creatures
5. Marine Plants of Rocky Shorelines
6. Caring for Rocky Shorelines
For further information on the Rocky
Shorelines protection and Education
project please contact:
Adam Gosling
WetlandCare Australia
PO Box 114 Ballina NSW 2478
T: (02) 6681 6169
E: [email protected]
W: www.wetlandcare.com.au
Prepared by S. Haigh, WetlandCare Australia
(Version 10/09) Photos: Adam Gosling
WetlandCare Australia: Supporting the community to protect and restore Australian wetlands since 1991