Coastal Habitats – The Occupants

A habitat is the environment where a population of plants or animals lives and grows. Sometimes it is difficult to say where one habitat ends and another begins, so we have chosen the major coastal habitats found around Australia.



seagrass_underwater_2What are they?
A mangrove is a type of tree that lives between the sea and the land, in areas that are flooded and drained by tidal waters. There are over 30 species of mangroves in Australia. While most trees would drown in such a salty water-logged environment, the mangrove has adapted to this environment in amazing ways, such as developing pneumatophores (breathing roots).

What lives there?
Mangroves provide a sheltered area for a large variety of marine animals. The floor of the mangrove forest is home to many marine worms, crabs, crustaceans and snails. The juveniles of fish, such as garfish, find shelter and food among the mangrove roots. At low tide, fish concentrate in the deeper tidal creeks that drain the mangrove forest. At high tide, larger fish and dolphins are able to move along these creeks, and into the forest itself, to feed.

Where are these habitats?
There is only one type of mangrove, the grey mangrove (Avicennia marina) found in South Australia . Near Adelaide , mangroves can be found along parts of the Port River and Barker Inlet. One of the most visited mangrove forests found along the Adelaide coastline is north of the city at St Kilda, where you can take a guided tour along the boardwalk trail through the mangrove forest.


Seagrass Meadows

What are they?
Seagrasses are flowering plants with roots that grow on the sandy floor of marine environments. They are quite different to seaweeds, which are a type of algae. To grow, they need sunlight and a small amount of nutrients. Seagrasses are very important in the coastal environment because they are a source of food and shelter, they oxygenate the water, trap sand and recycle nutrients.

What lives there?
Seagrass meadows are full of marine life such as seed shrimps, bristle worms, sea snails, sea stars, sea urchins, sponges, anemones, sea cucumbers and oysters. Larger animals, such as fish, squid, octopus, crabs, sharks, stingrays, dolphins and sea birds also visit the meadows. In non-tropical meadows, leatherjackets, garfish and swans eat large quantities of seagrass, but most animals can only digest seagrass leaves when they have broken down. Seagrass meadows are often called nurseries because so many types of animal, including snapper, garfish and shrimp, grow up there.

Where are these habitats?
Some of the most extensive seagrass meadows in South Australia are found in Gulf St Vincent, the body of water off the Adelaide coast. The meadows, which are usually no more than 50m offshore, are well known to snorkellers, but most people are more familiar with the dead seagrass that has washed up on the beach. Eleven species of seagrass are known to occur in South Australia , covering an area of approximately 9620km².


Open Ocean

What is it?
Most of us have seen the ocean as we’ve walked along a beach or gazed out over the waves towards the horizon. But where does the beach end and the ocean begin? If you were to swim out into the water, you would know you’ve reached the open ocean when light penetration, temperature and salinity stays almost exactly the same all year round. The open ocean is one of the most uniform environments on earth.

What lives there?
Residents of the open ocean include whales, dolphins, fish, squid, jellyfish, small crustaceans and microscopic plankton, which include the juveniles of many larger species including sea stars and lobsters.

There are many web sites dedicated to the creatures of the open ocean and their conservation.
Where are these habitats?
Gulf St Vincent , the water out from Adelaide ’s coastline, is too sheltered to be open ocean. Between summer and winter in one year, the temperature can change as much as 15°C and the salinity also varies widely. However, other less sheltered parts of South Australia ’s coast line are met by the Southern Ocean and the open ocean is no more than 500m out to sea.


Rocky Intertidal Shores

What are they?
Rocky shores may be a rock platform, rocks on a sandy beach, or areas completely covered in individual rocks ranging from boulders right down to pebbles. Sometimes they have rock pools that form in or among the rocks at low tide. The intertidal zone is the area of the shore covered by the normal high tide and exposed by the normal low tide. Therefore, it is an area that includes almost fully marine to fully terrestrial environments. The intertidal area can be divided into smaller zones according to how long they are under water during a tidal cycle. Exposure time is one factor that affects where animals are able to live.

What lives there?
Rocky shores have many different types of snails as well as barnacles, mussels, tube worms, isopods, chitons and sea squirts. When you visit a rocky beach you may be lucky enough to spot a small fish, sea urchin, sea star, snail or crab in a rock pool.

Where are these habitats?
Marino Rocks is the only rocky intertidal shore in the Patawalonga, Torrens and Port catchments.


Temperate Reefs

What are they?
Temperate reefs are usually formed from rock, although jetty pylons and other hard structures often support the same animals and could be called mini-reefs. Many of the rocks that form our reefs are made from the limestone remains of ancient marine organisms and sediments. There are also barr iers along our coastline that are designed to protect the beach from wave action but, over time, marine animals attach themselves to these hard surfaces and create a colourful artificial reef environment.

What lives there?
Reefs are home to a wide range of animals, from colonies of sponges, sea squirts, bryozoans and corals to anemones, crabs, abalone, snails, lobsters and cave fish.
Where are these habitats?
One of the northern-most temperate reefs in South Australia is at Semaphore. This reef is a series of flat rock platforms broken into strips by patches of sand. In contrast, a series of huge cement blocks were placed offshore in line with the Glenelg jetty to form a breakwater, which is now a popular snorkelling spot. Further south are two natural reefs at Hallet Cove and Port Noarlunga. The Hallet Cove reef is about 50m offshore, rising 1-2m above the surrounding sand while Port Noarlunga, Adelaide ’s most popular diving reef, is about 5m from the end of the jetty and is mostly exposed at low tide. It is located within a marine reserve and has an underwater interpretive trail.


Beaches And Dunes

What are they?
A beach is an area along the coastline that has a build-up of sand. Most of the Adelaide coastline is made up of beaches, which are shaped by a wave action called longshore drift. This process moves sand northwards along the coast. At the northern end of Adelaide ‘s coastline, beaches are generally wide and sandy, while at the southern end they are generally narrow and rocky.

Sand dunes are areas where sand has accumulated to form a series of ridges. A healthy sand dune system has at least three dunes and swales, and a range of dune plants. A swale is the lowest point in the dune.

Sand dunes are important because they:
Protect areas behind the dunes from storms and large waves.
Store sand for beaches that have had sand stripped away by waves.
Provide shelter, food and breeding sites for many birds, reptiles and insects.
Did you know?
Beach sand comes from many sources, including creeks and rivers, cliff faces, sand bars, seagrass and shells. Sand is also supplied to our beaches artificially. We move sand between beaches or pump it from the sea onto the beach because the changes we’ve made to the coast mean there is not enough sand available to maintain them naturally. Much of the sand in the coastal system is trapped under roads and houses or held back by walls.
What lives there?
Sandy beaches are home to a surprising number of animals that visitors usually don’t see because they are microscopic or hiding. Creatures that burrow into the sand include crabs, marine worms, copepods, amphipods, nematodes and molluscs (see photo). Washed up seagrass and seaweed is also a habitat for beach creatures and a temporary shelter for animals, such as sea stars, starfish and urchins, that have been washed ashore.

Sand dunes, and the plants which grow on them, provide food, shelter and shade for a range of insects, reptiles, birds and mammals.
Where are these habitats?
Beaches are easy to find along Adelaide ’s coastline, as you may know from swimming in the warmer months. Some of the most popular swimming beaches are Brighton , West Beach and Glenelg. Sand dunes are harder to find. There are remnant sand dunes at Tennyson, West Beach and Osborne. Many councils, such as Holdfast Bay , are now actively re-establishing sand dunes at beaches such as Brighton .



What are they?
An estuary is where a river or creek meets the sea, where the fresh water and salt water mix. They are always changing- from salt water to fresh water, from tidal to non tidal, and from wet to dry. Estuaries can vary in size, salinity and flow.

An estuary is an enclosed coastal body of water that is part land…. part waterway…. part sea…..

What lives there?
Many crustacean and fish species spend their early life stages in the protected nutrient-rich waters of estuaries, before moving offshore into deeper water or upstream into rivers. Estuaries are essential feeding, breeding and nursing areas for many commercially important fish and crustaceans. Some of the species found in the Barker Inlet and Port River Estuary include the western king prawn, black bream, blue swimmer crab and yellow-eye mullet. For bird lovers, white bellied sea eagles, pelicans and silver gulls can be seen resting and feeding around the estuary. The estuary is also home to a population of bottlenose dolphins. The presence of these dolphins living so close to urban/industrial development is thought to be internationally unique.
Where are these habitats?
The Barker Inlet and Port River Estuary are part of an interconnected system of tidal creeks and channels that open up into the Gulf St Vincent. The shoreline consists of wide tidal mudflats that are framed by salt-marsh, grey mangrove forests, wetlands and low-lying sand dunes. All these habitats play an important role in this unique ecosystem.

Visit the Port River mouth at Outer Harbor to see where the river meets the sea, or go for a tour through the Barker Inlet Wetlands located 12kms north west of the Adelaide Mangrove forests can be visited from Garden Island and Torrens Island , North Arm Creek and St Kilda.
Port Adelaide River system

The Barker Inlet and Port River estuary system is unique in that it is also home to a number of large industries, including coal handling facilities, cement works, electricity generating plants, salt harvesting, boat building facilities, sewage treatment plants, chemical plants and rubbish dumps.


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