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Grey mangrove
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- Grey mangroves are common in Queensland.
Avicennia marina (grey mangrove) belongs to the family Avicenniaceae. It is the most common and widespread mangrove found along the mainland coast of Australia. It is the only mangrove species able to withstand the cooler climate in South Australia and Victoria.
Grey mangrove occurs in intertidal zones on a range of soft muds to sandy soils. It is common along the tidal margins of estuaries and along saline or brackish river areas where it may grow with river, red and other mangrove species. A pioneer species, grey mangrove commonly colonises developing mud banks.
Description
Grey mangrove grows to 25 metres high, however trees of 10 to 15 metres are common in Queensland under favourable conditions. Trees have a large trunk which is covered by light-grey, finely fissured bark supporting a spreading leafy crown.
Leaves measure up to 8cm long and 5cm wide, are oval, pointed and arranged opposite one another on the stems. The leaves are glossy green above with a distinctive pale and slightly hairy, grey underside. Stomata (pores) and salt glands are scattered over the entire leaf surface but are more abundant on the underside. Flowers are small, yellow and appear in clusters.
A distinguishing feature of this species is the numerous spongy pencil-like pneumatophores (peg-like roots) which spread out from the base of the trunk. Pneumatophores originate from horizontal underground lateral roots and grow vertically through the soil surface to allow the mangrove roots to breathe.
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- The peg-like roots of the grey mangrove can form a dense covering over the ground.
Flowering and fruiting
Flowering occurs mid to late summer. Pale green flattened fruits (3cm long and 2cm wide) consist of a thin, hairy seed coat and enclose two closely folded seed leaves. The seeds germinate while attached to the tree (vivipary), which allows for quick establishment once the seed settles.
Salt tolerance
As a pioneer species, grey mangrove is very tolerant of extreme saline conditions by actively resisting the uptake of salt at the roots. Grey mangroves can also withstand short periods of inundation by freshwater or hypersaline water (salinity exceeding that of seawater). However, all mangroves are susceptible to extended periods of water logging, with death occurring within 14 days.
Uses
Australian Aboriginals and Europeans used grey mangrove timber for shields and in boat building respectively due to its light weight and strength. Grey mangrove timber was an important resource for oyster growers in the 1900s, which led to the protection of mangroves under early fisheries legislation.
The grey mangrove stabilises river banks and channels, providing areas for spat settlement in oyster culture, is a source of pollen for bee keepers, and provides suitable habitats for waterbirds and juveniles of important recreational and commercial fish species. Grey mangroves also increase amenity value for our waterways by screening development and buffering storm surges and wind.
Related information
- Red mangrove
- River mangrove
- Orange mangrove
- Yellow mangrove
- Milky mangrove
- Protection and management
- Saltmarsh, seagrass and algae
- Field guide to the common saltmarsh plants of Queensland
- Fisheries development
Page maintained by Rebecca Batton and Dawn Couchman
Last reviewed 08 August 2007
