Human
Influences

Australia’s mangrove habitats are influenced profoundly and decisively by human attitudes of the day where different communities have quite distinct management practices. Such practices closely match cultural attitudes to reflect current socio-economic pressures combined with community awareness of the benefits and vulnerability of mangroves.

Over time, these can, and must, alter and adapt to reflect new or anticipated conditions – especially if we wish to preserve and sustain the rich natural heritage of mangroves in Australia.

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Threats & Pressures

Mangrove dieback

Top - Mangroves respond to deteriorating conditions with dieback and loss of habitat.

Mackay dieback

Top - Avicennia marina (lighter trees) has been specifically affected by agricultural runoff in the Mackay region, Queensland.

The arrival of Europeans in the eighteenth century saw the alteration of estuaries in southern and eastern Australia. As population growth increases along Australia’s coastline there has been a corresponding increase in usage and development. Coastal natural resources including mangroves have come under increased risk, particularly near large urban centres. Degradation of mangrove habitat by the direct loss or alteration of trees reduces its capacity to function effectively as a viable ecosystem. This in turn endangers the species that depend upon the healthy mangrove ecosystems. While it is currently estimated that none of Australia’s mangrove species are at risk, the coastal zone they occupy has the greatest number of threatened species. One example is the rare and endangered Rusty Monitor, Varanus semiremex - a small crab-eating goanna restricted to hollow trees in mangroves of north eastern Queensland. One of the few mangroves to have suitable hollows for this monitor, is Avicennia marina, the species threatened most by chemicals in agricultural runoff. The chief threats to mangrove habitat come from: conversion and landuse change and the indirect effects of sediments and chemicals in runoff from catchments degraded by clearing of upland vegetation and intensive agriculture.

Conversion and Landuse Change

Around 17% of Australia’s mangroves have been destroyed since European settlement. Mangroves near developing centres have been systematically destroyed and damaged. Moreton Bay, for example, is situated near the city of Brisbane where an estimated 20% of the pre-European mangrove area has been subject to reclamation landfill.

Compared with other countries, however, these impacts are relatively low. This is largely because most of Australia’s mangroves are located in the more sparsely populated northern regions of the country, like north Queensland, the Northern Territory and northern Western Australia. Mangrove forests in these regions have largely remained pristine, or in near pristine condition. But, where development has taken place, then the effects on mangroves is usually severe. For example, the development associated with the expansion of the Northern Territory’s major population centre of Darwin has resulted in the clearing of 2% of the pre-European area of mangroves in the harbour area.

Rusty Monitor The Rusty Monitor, Varanus semiremex, is rare and threatened because it depends on mangroves. Photo: Kieren Aland

Indirect Impacts of Sediments in Runoff

Increased sediment loads in catchment runoff are affecting mangrove distributions within estuaries. In recent decades, there have been unprecedented gains in mangrove areas at the mouths of at least four Queensland river estuaries, including Trinity Inlet, Pioneer River, Johnstone River, and Fitzroy River. It is expected that the pattern is similar in other states. The increase in such mud banks is indicative of increased clearing of catchment vegetation, and the construction of barrages and dams.

Indirect Impacts of Chemicals in Runoff

Agricultural chemicals in runoff appear to affect mangrove health. In five adjacent estuaries in the Mackay region of Central Queensland, more than 30 km2 of mangroves have been affected by the severe dieback of Avicennia marina. Twenty other species appeared unaffected, but A. marina occupied about 50% of the total mangrove area. Correlative evidence implicated herbicides used in sugar cane production as the most likely cause of this dieback. Key indicators of mangrove plant health were correlated with diuron concentrations in sediments, and planthouse trials demonstrated that salt-excreting mangroves like A. marina were more affected by herbicides than the more salt-excluding species.

  • Landfilling mangrove areas like Port Curtis QldLandfill of mangrove areas continues in developing industrial areas like Port Curtis in Queensland.
  • Mud seedlingsDepositional banks like those in the Fitzroy River, Queensland, are rapidly colonised by mangroves.

Community Volunteers

A key feature of MangroveWatch is its close partnership between community volunteers and scientists from the James Cook University’s Mangrove Hub. Together they are systematically recording basic data as video and still imagery for assessments of estuarine habitat health.

Armed with expert support, training and advice, MangroveWatch volunteers in key regions are actively contributing to the monitoring of local estuaries and shorelines. An important goal in this phase of the program is to develop a network of like minded groups with the aim of producing public documents that describe important issues affecting local estuaries and mangroves, and their overall health.

Getting Involved

If you would like to find out more about us or if you like to initiate your own MangroveWatch group within your area, please contact someone at the Mangrove Hub. We will be happy to help.

  • Mangrove Hub Facilitator
  • Dr Norm Duke
  • MangroveWatch Ltd
    ABN: 44 153 297 771
  • PO Box 1250,
  • Elanora Q 4221
  • Mangrove Hub Email

Mangrove Watch Brochure

You can download our fact and information sheet (see link below) to get more information about the MangroveWatch programs.

Mangrove Watch Brochure