Educational Material

Seagrass Beds - Pastures of the sea

Support environment groups such as National Parks Association of NSW in calling on the NSW Government. NPA seeks to preserve at least 20% of all NSW marine habitat types (including seagrass beds) as No-take Sanctuaries.

If seagrasses are to be protected, they need special areas where damaging activities cannot occur.

What are Seagrasses?
Seagrasses are flowering plants that grow below the high tide level. They occur in the sheltered shallow waters of estuaries, generally in soft sediments like sand or mud.

Like any plant, seagrasses need light to grow and are usually restricted to the upper two metres of water where there is sufficient light. Seagrasses have either straplike or paired oval leaves; they grow from rhizomes (underground stems).

Seagrasses Save the Sea
Seagrasses are vital for the ongoing health of our coastal waters and fisheries. They stabilise the sand and mud in which they grow, and provide food, shelter, breeding grounds and nursery areas for many marine organisms such as fish and prawns.

Shelter
Seagrass beds are valuable fish habitats. They provide shelter for many different small animals and plants, and also provides protection for small fish from larger predatory fish.

Breeding Grounds
Seagrass beds provide breeding areas for many species of fish, and act as a nursery for juvenile fish, crabs and prawns. Young prawns hatch in the open ocean and rapidly make their way to coastal seagrass beds where they mature until they are large enough to return to the open sea. Juvenile mullet, tailor, bream and flathead depend on seagrass beds for protection.

A source of oxygen
One square metre of seagrass beds produce up to 10 litres of oxygen each day.

A source of food
Seagrass leaves grow fast, producing a great amount of organic material. A single hectare of seagrass meadow may produce up to 20 tonnes of leaf material each year. Green turtles, swans, many invertebrates and some fish feed directly on seagrass.

Decaying seagrass leaves also provide food for small animals such as crustaceans, molluscs and worms. These in turn are eaten by fish, prawns and birds. In Port Hacking, 65% of the food eaten by leatherjackets are the small plants and animals living on the seagrass.

Improving Water Quality & Protecting Shorelines
Seagrasses improve water quality by slowing down currents and allowing suspended particles to fall to the bottom. Seagrasses encourage the building up of bottom sediments which reduces erosion and protects shorelines.

Where are the seagrasses in NSW?
Seagrasses are found mostly in estuaries and shallow coastal waters with sandy or muddy bottoms. The plants usually live together in 'seagrass beds' or 'seagrass meadows'.

There are six species of seagrasses on the NSW coast. Areas with a coverage of more than 5 square km include Jervis Bay, Botany Bay (Sydney) and Lake Macquarie. The largest single area of seagrass in NSW is found in Wallis Lake, Forster. This contains 21% of the state's total seagrass. NPA is currently campaigning to include this lake in the Manning Shelf Marine Park.

For more information on Wallis Lake click here.

There is no point protecting individual marine species if we are not protecting the habitats in which they need to survive.
At least 20% of each habitat type needs FULL protection,in No-take Marine Sanctuaries.

Seagrass Beds - A Fragile Habitat
Seagrasses are fragile fish habitat and can be easily destroyed. Many major estuaries in NSW have lost as much as two-thirds of their seagrass beds in the past 30 to 40 years.

Although the leaves of the seagrass grow fast, the rhizome grows relatively slowly. As a result, once seagrass meadows are damaged, their recolonisation is very slow. Seagrass beds in Jervis Bay which were destroyed by seismic blasting in the 1960's have still not recovered.

Seagrasses generally occur where there are slow currents. Where the speed of flow has increased due to removal of sand, rock or other seagrass beds, seagrasses often cannot re-establish from seed.

How does damage to Seagrass Habitat occur?
The main reasons for loss of seagrass beds are loss of light due to sedimentation, and algae growth due to increased nutrient levels in the water. This occurs when:
- land is reclaimed for waterfront developments;
- dredging occurs and when weirs are built;
- algal blooms occur due to pollution runoff from sewage, factories, stormwater etc;
- vegetation is cleared along river banks and sediments run off;
- boat anchors, chains, and propellers drag across the seagrass beds;
- bait digging and trawling occur across fragile seabeds.

The NPA Marine Campaign

National Parks Association is campaigning for a system of sanctuaries to be established which together include at least 20% of the total area of each marine habitat within both the Commonwealth and State Territorial .

Back to Top

Back to Educational Material