Mangrove communities are one of the most interesting, complex and important ecosystems on the Earth. Being muddy, smelly and less attractive than sandy beaches, mangrove habitats were often cleared before we started to understand their importance. Here is some information about mangrove ecosystems, mangrove root systems, seeds, destruction and conservation, and different species that are found in Australia like red mangrove tree and others.
What is a Mangrove Plant? The most important characteristic of a mangrove plant is that it tolerates salt water. Mangrove plants are not necessarily related to each other. While many other plant groups consist of plants that are evolutionary related, such as eucalypts, acacias or bottle brush plants, mangroves are any types of trees that tolerate salt water. The interesting thing about them is that they don’t favour salt water, they would grow in fresh water – if only they were better competitors. They grow in the tidal salty waters because of the lack of competition from other plants that are not able to tolerate such amounts of salt.
Zoning in Mangrove Communities Mangroves use different strategies to deal with salt. Some are able to exclude salt from the intake by their roots, others have special salt glands that excrete salt. Yet others exclude salt via their leaves. Because different mangrove species are able to tolerate different amounts of salt, mangrove communities tend to have a zoning of different species parallel with the coastline. Grey mangroves are usually found closest to the water. Further away is a zone of red mangrove tree, and highest up on the slope are yellow mangroves. These are the most salt-tolerant species as highest tides bring the salt here, but it’s not rinsed out as often as lower down towards the water. Higher up the slope behind the mangrove zones are often saltmarsh and casuarinas.
Red Mangrove Tree and Other Australian Species Mangrove communities are generally found along the northern coasts of Australia. Grey Mangrove (Avicennia marina), a species with leaves with grey underside, is the most common mangrove in Australia. It is found along all the northern coasts, and as far south as Shark Bay in Western Australia; New South Wales – Victoria border in eastern Australia, and in a few pockets along the coasts of Victoria and South Australia.
River mangrove (Aegiceras corniculatum) is another species that reaches quite far south along the coasts of Australia, but not quite to Victoria and South Australia.
Red Mangroves and Black mangroves are more tropical species and restricted to further north. Red mangroves (Rhizophora stylosa) are found along the whole coast of Queensland and Northern Territory, and parts of the coast of northern Western Australia.
Black Mangrove (Bruguiera gymnorrhiza) is found along the eastern coast of Queensland, and the top end of Northern Territory.
Mangrove Root Systems Because mangroves live on the coasts with tidal waters, they have to have strategies to cope with the lack of oxygen to their roots in the muddy ground that is often under water. Different species have different ways to get their roots above the water level, at least at the low tide. Grey Mangrove has got special pneumatophores (below) growing out of their roots and sticking out from the water. Red mangrove tree has so-called stilt roots (above) that are high enough up to be above the water level. Other species, like Looking-glass Mangrove (Heritiera littoralis) has got buttress roots, similar to rainforest trees. Rainforest trees have the buttress roots for the same reason – the ground gets too wet when it rains a lot.
Mangrove Seeds and Importance of Mangrove Habitat Mangroves also have clever strategies when it comes to seed dispersal. Their seeds can float in the water and they can travel very far in the water. Other species that reproduce and live in and around mangrove ecosystems are mangrove crab, fish like barramundi, oysters, snakes, crocodiles and many shore birds but also terrestrial birds and animals. Mangroves provide habitat, roosting and nesting sites for many shore birds, and many migratory species. It is a very complex system where mangroves act as nurseries for the young of many animals and support the whole estuarine food web. In addition to that, mangroves act as a barrier against storms, tropical cyclones (hurricanes) and flood destruction; and they are an important filter of pollution like urban or industrial runoff.
Mangrove Destruction and Conservation Before we learned how complex and important the mangrove ecosystems are, a lot of mangrove habitat was destroyed for mangrove wood; and often it was cleared simply because they were muddy and smelly areas, much better to turn into sandy beaches. As late as years before the 2000 Sydney Olympics, parts of the Homebush mangrove ecosystems were cleared because the space was needed for building the Sydney Olympic Stadium. Other things that destroy intertidal wetlands are oil spills; engineering works that increase siltation, removal of freshwater flows and removal of inundation. A big part of mangrove conservation is to transplant saltmarsh which is more vulnerable than mangroves themselves, to maintain balance between the two.
NOTE: This website is written in British English, which is the English we use in Australia. You will find words like "traveller", "harbour" and "realise", and they are all correct in the language used in Australia.
