Grey mangrove fact sheet | Field of Mars EEC

What are grey mangroves?

Grey mangroves are native mangrove trees that grow along sheltered coastal rivers, creeks, estuaries and bays. Their scientific name is Avicennia marina. In NSW, grey mangroves commonly grow as shrubs or small trees with grey bark, glossy green leaves and pale grey, slightly hairy leaf undersides.

Grey mangroves are one of the most common mangroves in NSW and grow in intertidal wetlands where salty water and fresh water mix. Around Sydney, they are important plants in mangrove forests along waterways such as the Lane Cove River and Parramatta River. Their roots help stabilise muddy shores, trap sediment and create habitat for many animals.

A grey mangrove.

Grey mangrove leaves have glossy green upper surfaces and pale grey, slightly hairy undersides.

Where do grey mangroves grow?

Grey mangroves grow in intertidal zones, which are areas covered by water at high tide and exposed at low tide. They are usually found in soft mud, fine sediments or sandy mud along estuaries, tidal creeks, sheltered bays and riverbanks. These habitats are salty, wet and low in oxygen, so only specially adapted plants can survive there.

In Sydney, grey mangroves are important plants in mangrove forests along the Lane Cove River, Parramatta River and other sheltered waterways. They can grow near coastal salt marsh and sometimes spread into saltmarsh areas when conditions change.

Grey mangroves grow in intertidal wetlands where muddy ground is covered and uncovered by the tide.

How are grey mangroves used by Aboriginal Peoples?

Mangrove forests are important cultural landscapes for many Aboriginal Peoples in coastal parts of Australia. Around coastal Sydney, Aboriginal People used estuaries and shorelines for fishing and collecting shellfish and other foods. Mangrove and estuary habitats should be understood as part of wider Country, not only as places where useful resources were found.

Some historical sources also record grey mangrove timber being used to make shields in the Port Macquarie district. This is a regional example from the NSW north coast, so it should not be presented as a use by all Aboriginal Peoples or as specific to the Darug or Sydney area.

Mangrove forests are culturally important coastal places and provide many natural resources.

What animals use grey mangroves?

Many animals use grey mangroves for food, shelter, hunting or breeding. Fallen leaves, twigs, flowers and fruits become mangrove leaf litter. Bacteria, fungi and algae help break this material down, and detritivores such as red-fingered marsh crabs, semaphore crabs, prawns, snails and other molluscs feed on the decaying plant material.

Grey mangrove roots create shelter for small fish, crabs, oysters, barnacles and other invertebrates. Waterbirds feed among the mud and roots, spiders attach webs to branches, and insects visit the flowers for pollen and nectar. Mangrove forests also provide nursery habitat for young fish and crustaceans.

Crabs help break down grey mangrove leaf litter and recycle nutrients in the mud.

What is the life cycle of grey mangroves?

Grey mangroves produce small flowers that can be pollinated by insects. After pollination, the flowers develop into pale green, hairy fruits. Each fruit contains one seed. The seed begins to germinate while it is still inside the fruit and attached to the parent tree. This is called vivipary.

When the fruit falls, it can float and be carried by the tide. Some seeds are eaten by crabs or wash into unsuitable places, but others settle in soft mud and begin to grow. Young seedlings may remain small for a long time under the shade of adult trees. When light becomes available, such as after an old tree falls, some seedlings grow into mature grey mangroves.

Grey mangroves produce small cream to yellow flowers that can attract insect pollinators.

Grey mangrove seeds are carried by tides and may settle in mud near breathing roots.

New grey mangrove seedlings grow from seeds that settle in suitable mud.

What adaptations do grey mangroves have to help them survive?

Grey mangroves grow in mud that is often covered by tides and has very little oxygen. They survive by growing many pencil-like breathing roots called pneumatophores. These roots stick up from the mud and take in oxygen through tiny pores called lenticels. The oxygen then moves through spongy tissue to the underground roots.

Grey mangroves also have adaptations for living with salt. Their roots can help limit the amount of salt entering the plant, and special glands on the leaves can release excess salt. Their thick, leathery leaves also help reduce water loss. Releasing partly germinated seeds helps young plants establish quickly when they settle in a suitable muddy place.

Pneumatophores help grey mangrove roots take in oxygen from above the mud.

Why are grey mangroves important?

Grey mangroves are important because they help protect shorelines. Their trunks, roots and breathing roots slow water movement, trap fine sediment and help hold muddy banks together. This can reduce erosion from tides, waves, floods and storm surges.

Grey mangroves also support estuary food webs. Their fallen leaves and twigs become food for decomposers and detritivores, which are then eaten by fish, birds and other animals. Mangrove forests provide habitat for shellfish, crabs, spiders, insects, waterbirds and young fish. They also help filter water and store carbon in plant material and wetland soils.

Grey mangrove seedlings show how mangrove forests can regenerate where seeds settle in suitable mud.

How can you help grey mangroves?

You can help grey mangroves by staying on tracks, paths and boardwalks when visiting mangrove forests. Walking through mangrove mud can crush seedlings, damage breathing roots and disturb crabs, snails and other small animals.

Keep litter, chemicals, oils, garden waste and soil out of gutters, drains, creeks and rivers because stormwater can carry pollution into estuaries. You can also help by learning to identify local mangrove plants, observing wildlife without disturbing it, joining local bushcare activities and supporting the protection of coastal wetlands.

Boardwalks help people explore mangrove forests without trampling mud, seedlings or breathing roots.

Related fact sheets

More plant fact sheets

• Plant fact sheets – Explore native plant fact sheets about shrubs, trees, grasses and other plants of Sydney and NSW.
• Swamp she-oak fact sheet – Compare another wetland tree that grows near water and supports wildlife.
• Paper-bark tree fact sheet – Learn about another moisture-loving tree that provides habitat and shelter.

Habitats and ecosystems

• Mangrove forest fact sheet – Learn about the intertidal forest habitat where grey mangroves grow.
• Coastal salt marsh fact sheet – Explore a nearby tidal wetland habitat that can occur beside mangroves.
• Water habitats fact sheet – Find out how water habitats support animals, plants and life cycles.
• Field of Mars Reserve fact sheet – Learn about local bushland, wetlands, creeks and mangroves in the Lane Cove River catchment.

Animals that use this habitat

• Red-fingered marsh crab fact sheet – Learn about a mangrove crab that feeds on plant material and recycles nutrients.
• Semaphore crab fact sheet – Explore another crab that lives in soft mud around mangroves and estuaries.
• Australian white ibis fact sheet – Learn about a native waterbird that feeds in wetlands and muddy places.

Food webs and ecological relationships

• Invertebrate fact sheets – Explore crabs, insects, spiders, molluscs and other small animals connected to food webs.
• Golden orb weaving spider fact sheet – Learn about a spider that can attach its large webs to trees and shrubs in wetland edges.

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