Rocky shore
Rocky shores are found where the sea meets the land. They support a diverse mix of plants and animals which have adapted to survive this habitat's unique conditions. Constant wave action and the rise and fall of tides make these shores tough places to live.As well as supporting lots of unusual plants and animals, rocky shores are important fish nurseries and roosting and feeding grounds for birds. Along with their commonly associated algal beds, they also help stabilise inshore sediments.
Because big parts of rocky shores are exposed at low tide, they’re great places to study marine life, though you need to take care of yourself and this sensitive environment.
Forces shaping the rocky shore
A combination of waves and tides shapes the rocky shore and influences what
species can survive there.
Waves
Wind blowing across the ocean forms peaks and troughs in the water surface which
appear to travel as a wave. Along rocky shores there isn’t enough room
for water to move freely, so waves break over the rocks. Plants and animals
living on rocky shores have adapted to being pounded by waves.
Tides
The tide's rise and fall is one of the main factors affecting life on rocky
shores. When the tide falls, plants and animals on rocks are exposed to air.
They must develop special adaptations to survive until the tide comes in again.
When high tides aren’t very big, plants and animals which live high on the shore may be exposed to air for several days. Organisms which live very low on the shore may only occasionally be exposed to air.
Rocky shores as ecosystems
Many animals and plants live on rocky shores in the area between high and low
tide called the intertidal zone. These organisms must be able to cope with problems
of not one environment, but two. They are pounded by waves, exposed to extremes
of temperature and salinity, and flooded by sea water and exposed to drying
air twice every 24 hours. They also have to avoid being eaten by birds, molluscs
and crabs at low tide, and by fish and other marine life at high tide.
Several distinct habitats exist in rocky shores, each with its own survival challenges for plants and animals living there.
Platforms
These are formed when waves, wind and rain carve rock into flat platforms. Often,
the back of the rock (the bit which hasn’t been eroded yet), forms a cliff,
while the ocean edge of the platform steps down into the water. This means one
rock platform can support many different kinds of plants and animals, because
some sections are almost always under water, while other parts are usually dry.
Rock pools
These are usually formed when a boulder lodges in a depression in the rock and
grinds a hollow as it rolls around in the waves. After some time, the depression
becomes deep enough to hold water during low tide. If the boulder stays in the
pool it will gradually grind it deeper, but sometimes, a big wave washes the
boulder out and the rock pool stays shallow.
Because pools trap grit, stones and boulders, only certain plants and animals can survive in them. The grit smothers some organisms, while stones and boulders rolling around in storms can smash delicate creatures.
Boulder fields
Groups of boulders are found where little wave action occurs, and the shore’s
not too steep.
During storms, the boulders roll around and flip over, smashing any animals living on their underside or the rock bottom. Animals and plants which were on top of the boulder may find themselves having to cope on the bottom, in the dark and permanently under water. And anything which lived on the bottom will be exposed to air, sunlight and heat.
Since sand gathers inside boulder fields, abrasion increases, smothering some plants and grinding others.
Nature’s survival tricks
Special adaptations enable animals and plants to live in these conditions.
Many animals avoid sun, drying air and predators such as birds, by staying in cracks, under rocks or in their own burrows at low tide. Some sessile animals such as barnacles and oysters close their valves tightly to avoid drying when the tide goes out. They come out to feed when covered by water.
Others may be well camouflaged and appear to be invisible.
Organisms which are constantly pounded by waves are often very tough, so it doesn’t matter if they’re hit hard. Others are flexible or flat, so they bend instead of breaking when they’re hit, or don’t get hit at all.
Rocky shore dwellers
Seaweeds
Most plants found on rocky shores are seaweeds. They’re algae, which means
they can live on hard surfaces where plants with roots wouldn’t be able
to survive. Instead of roots, they have special suckers called ‘holdfasts’
which cling to rock, even in big waves. They don’t have flowers, or normal
stems or leaves. The bit that looks like a stem on some seaweeds is called a
‘stipe’. This joins the holdfast to the ‘frond’, the leaf-like
part. Seaweeds are mainly green, red or brown, depending on which wavelength
of sunlight they’re trying to trap. Not all seaweeds have long, floaty
fronds. The fronds can be tiny, so the seaweed looks like velvet covering the
rocks. Other may look like tiny cabbage leaves.
Lichens
These black, orange, yellow or grey plants are actually made up of a fungus
and a microscopic algae living together and sharing food and energy to grow.
They live at the top of the shore where the tide doesn’t rise and are the
only plants on a rocky shore which are not algae.
Microscopic plants
Some rocks along the shore look bare. But that doesn’t mean there are no
plants living on them. If you look carefully at rocks in mid- to high tidal
level, you’ll notice they’re often yellowish or pinkish. This is because
they’re covered with microscopic plants, many of which are diatoms, tiny,
single-celled plants with hard silica shells. These plants are the main food
for many grazing animals on rocky shores.
Grazing snails and limpets
Many species of these animals live on rocky shores. They eat microscopic plants,
lichen or seaweed, depending on which part of the shore they inabit. Limpets
are snails which have a cup-shaped shell instead of a coiled one. They use a
large, flat foot to tightly clamp the rock.
Barnacles
Barnacles attach themselves to one spot on the rocky shore and never move, not
even to feed. Using specialised legs, they catch food as it floats by in the
waves. Barnacles’ shells are made of several plates. Their size and shape
depends on whether they’re exposed to big waves.
Sea squirts
Also known as cunjevoi, sea squirts are similar to barnacles in that they’re
both filter feeders which stay in one spot. These animals pump large amounts
of water through their bodies while under water, and then filter the food out.
Since they store a lot of water during low tide, they squirt when you step on
them.
Sea squirts are an important food source and habitat, so if you destroy cunjevoi to use them as bait for fishing, you’re also wrecking the lives of many other creatures.
Anemones
The scientific name for anemones and corals is Anthozoa — Greek
for 'flower animals’. Although they are animals, anemones grow in forms
which resemble plants. An anemone is a single animal with a sack-like body and
tentacles around a single opening. Some are capable of sliding about very slowly.
In rock pools and on reefs just off shore, there are many species of anemone.
Why are rocky shores important?
As well as providing homes for many animals, rocky shores are also an important
nursery area for many fish and crustacean species.
Some of these species like to shelter by rocky shores, in areas where stands of seaweeds break the waves' power.
This habitat also provides lots of food for fish. The commercially important fish found around rocky shores include blackfish, yellowfin bream, snapper, tarwhine, trevally, yellowtail and sampson fish.
Algal beds of this habitat are an important food source for rare and threatened species like marine turtles.
And at low tide, wading birds love to feed on crabs and limpets on exposed rocks.
Good places to explore
Rocky shores are great places to observe a wide variety of plants and animals.
If you look closely at the shore at low tide, you’ll be able to watch lots
of animals moving and feeding. Remember, most creatures will try to hide from
the sun's heat, so explore this area when it’s cooler.
- Avoid reaching into crevices as blue-ringed octopus and some cone shells lurk there. They are highly poisonous.
- Always beware of waves crashing over rock platforms. Never turn your back to the sea when exploring a rocky shore. Stay away from these areas when waves are big.
- Wear safe footwear with good tread. Barnacles and oysters slice skin; wet, algae-covered rocks are slippery.
- If you do cut yourself, make sure you wash the cut and use an antiseptic to stop it becoming infected.
- Be sun sensible. Slip, slop, slap, and wrap (sunglasses).
Take care of the shore
- When looking at creatures of the intertidal zone, be careful not to disturb them.
- Don’t trample plants or animals. Leave rocks and shells exactly as you found them.
- Remember that creatures living below boulders are very sensitive to disturbance. Try not to move rocks, but, if you do, lower them carefully to the same spot to avoid moving or crushing whatever’s living on their underside.
- Walk to rocky shores from beaches or use formed stairways to avoid causing erosion.
- The number of shellfish or gastropods you can collect to eat or use as bait is restricted. In some areas you’re not allowed to take any. Contact your regional boating and fisheries patrol officer for details of bag limits and protected areas.
- Take your litter home with you. Remind other people to do the same.
- If you’re fishing, don’t throw your bait bags or other rubbish on the rocks or in the ocean. Take your broken fishing equipment home and don’t leave metres of snagged fishing line behind on the rocks.
Last updated: 28 November 2003
