Rocky shore

Factors influencing rocky shore habitats, plants and animals

Of the many factors that influence habitats, plants and animals on the intertidal rocky shores, energy forces (mainly as wave energy) and tidal inundation are very significant. Another factor or attribute influencing rocky shores includes the composition of the rock, which can determine how the rock breaks up into smaller components (e.g. boulders, cobbles, pebbles, gravel etc.).

Waves

Wind blowing across the ocean forms peaks and troughs in the water surface which appear to travel as a wave. Along the exposed southern coast of Queensland, waves can travel a long distance, and accumulate enough energy to be quite large. Waves break over rocky shores and plants and animals living on these places have adapted to being pounded by waves. Where waves splash higher on the rocky shore, animals take advantage of this splash zone.

In bays and estuaries, in the sheltered side of large islands (e.g. K'gari (formerly Fraser Island), Moreton and Stradbroke Island), and within the sheltered waters of the Great Barrier Reef lagoon, waves are generally smaller and more gentle. There is less wave splash and the intertidal area is mainly influenced by tidal inundation.

Waves can also be created by large storm events, such as cyclones and east coast lows which are exceptions to the rule for high energy and low energy rocky shores.

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.

Tides can also act as an energy force over the tidal cycle, such as during tidal ebb or flow when the water is rushing away from or towards the shoreline.

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 may be exposed to freshwater during rainfall or flood events. 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 microhabitats exist within rocky shore habitats, each with its own survival challenges for plants and animals living there. Some of these microhabitats have distinct shapes which influence how biota will survive there. Yet other microhabitats have high roughness where the terrain goes up and down, providing plenty of places for animals and plants (and water). The rocky microhabitats may have a different composition – for example, either land-based rock or carbonate.

Platforms

These are flat (planar) platforms that were formed when waves, wind and rain carved into rock. 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.

The type of rock (lithology) will influence the degree to which a platform is created. Platforms were formed through long term processes over geological time including previous exposure to wave action and the rise and fall of sea levels.

Rock pools

These are depressions 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.

Pebbles, Cobbles and Boulders

Rocky shores may include particles of rock, which vary in grain size. Largest of all are boulders, forming boulder fields. Next in size are cobbles, able to be flung up by waves. Smallest are pebbles. All provide spaces for animals and plants to hide, and for seawater to be retained.

On offshore coral reefs and inshore coral fringing reefs, the pebbles cobbles and boulders may be composed of carbonate created by coral animals.

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. The kinds of seaweeds that grow on high energy rocky shores of southern Queensland may differ from those of the low energy shores of bays and estuaries and further north within the Great Barrier Reef lagoon.

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 and cyanobacteria

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. Cyanobacteria, previously known as blue-green algae, can also grow, showing up as dark shadowy colours on the rocks.

Grazing snails, limpets and other molluscs

Many species of these animals live on rocky shores. They eat microscopic plants, lichen or seaweed, depending on which part of the shore they inhabit. 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. Snails and limpets of high energy shores may differ from those of low energy shores where they do not need to hang on so tightly. On low energy shores, oysters or mussels can form large reefs of their own in the intertidal and subtidal areas, full of nooks and crannies for animals to live.

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, shape and position on the shore depends on whether they're exposed to big waves and whether they are splashed by spray from the waves. Barnacles can be present in large numbers, occupying distinct zones on high energy rocky shores.

Sea squirts

Also known as cunjevoi, sea squirts are similar to barnacles in that they're both filter feeders which stay in one spot. Cunjevoi are usually found on high energy rocky shores. 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.

Corals

Hard and soft corals can occur in rock pools or in the lowest tidal areas in the warmer waters of the Great Barrier Reef lagoon as well as on the sheltered lee side of exposed rocky shores and platforms. These may include subtropical species that cover parts of the rocks, taking the shape of the rock; or they may be mainly tropical corals that form significant limestone structures of their own. Some hard corals look obviously stony, yet others have soft polyps which come out in the day, hiding their stony skeleton. Soft corals also come in similar leathery or feathery forms which hide the basic polyp structure.

Why are rocky shores important?

There are many places for animals to live among the rocks, platforms, depressions, cobbles, pebbles and boulders.

As well as providing homes for many animals, rocky shores are a productive food source and an important nursery area for many fish and crustacean species. 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.

Some of these species like to shelter by rocky shores, in areas where stands of seaweeds break the waves' power. 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.

Take care of yourself

• 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

• Before you undertake any activity in a rocky shore habitat, it is important that you first check whether it is located within a marine park. State Marine Parks cover a large proportion of Queensland’s east-coast and depending on the zoning and designated areas certain activities may be restricted.
• Declared Fish Habitat Areas provide protection of all habitat types equally (e.g. vegetation, sand bars and rocky headlands) from physical disturbance to sustain our fisheries. There are a number of declared fish habitat areas throughout Queensland.
• The number of shellfish or gastropods you can collect to eat or use as bait is restricted. Similarly collection of aquarium fish may be regulated. In some areas you're not allowed to take any fish, shellfish or gastropods. Contact your regional boating and fisheries patrol officer for details of bag limits.
• 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.
• 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.