The significance of mangroves to Port Stephens

STUCK IN THE MUD: Children show how easy it is to get stuck in the mud in Port Stephens due to a combination of suction and no solid base. Picture: Iain Watt
STUCK IN THE MUD: Children show how easy it is to get stuck in the mud in Port Stephens due to a combination of suction and no solid base. Picture: Iain Watt

The significance of mangroves to the Port Stephens estuaries and eco-system can never be underestimated, according to leading marine scientist and Soldiers Point resident Iain Watt.

In addition to their environmental and economic value, mangroves provide a rich pantry for many traditional foods and medicines, treating skin disorders, headaches, rheumatism and ulcers. And its uses dates back many thousands of years.

"In the Port Stephens area, the timber from mangroves had several valuable uses including making spears, paddles, boats, and latterly mangrove poles for the construction of oyster frames for the oyster industry," Mr Watt said.

"Yet with the increase of the coastal populations and the desire for, and perceived value of, coastal property the mangroves in Port Stephens, as elsewhere, remain under threat from sedimentation, pollution, 'discrete' clearing and misunderstanding."

"Fortunately, they are protected in NSW under the Fisheries Management Act 1994, because of their importance as fish habitat, as opposed to their intrinsic ecological and socio economic values.

"The maximum penalties under this Act for damaging mangroves without a permit from DPI are $220,000 for a corporate offender and A$ 110,000 for an individual offender."

Mr Watt believes there are now opportunities in Port Stephens to develop citizen science projects to improve the understanding and to support community conservation of the local mangroves.

"These should be explored further," he says.

Some of the mangroves extending along the Port Stephens coast adjacent to Mambo wetlands at Salamander Bay. Picture: Iain Watt

Some of the mangroves extending along the Port Stephens coast adjacent to Mambo wetlands at Salamander Bay. Picture: Iain Watt

He also has a stark warning for anyone visiting a mangrove area.

"Care should be taken to avoid the deep mud when visiting a mangrove, as once you sink up to your knees in the mud you will never be able to pull yourself out unless you get some assistance, due to a combination of suction and no solid base. I have seen people that had to be winched out of the mud horizontally having become inadvertently stuck."

Mr Watt says it is worth noting the history of mangroves in Port Stephens because they are very complex environments which require protection.

"Mangroves comprise several species of trees and shrubs that line the muddy banks of tropical and subtropical estuaries and tidal rivers," he said.

"At first they appear to be a chaotic tangle of plants, thick mud, smells and stinging insects, but they are in fact a highly evolved and organised ecosystem, able to occupy the harsh intertidal zone, where the sea meets the land.

"They can survive on sandy shores and thick smelly anoxic mud with reduced oxygen and increased sulphide, and they have developed shallow but extensive root systems to absorb gases from the air."

Australia has the third largest area of mangrove in the world, after Indonesia and Brazil, totalling around 11,200 square km. Port Stephens hosts two species of mangrove; the grey mangrove (avicennia marina) and the river mangrove (aegiceras corniculatum).

Information on mangroves outlined on a board in the Mambo Wetlands in Salamander Bay.

Information on mangroves outlined on a board in the Mambo Wetlands in Salamander Bay.

"Most plant seeds germinate in the soil, but mangroves are viviparous and their seeds germinate on the tree, creating a propagule before release. The propagules of the Port Stephens mangroves have very different and distinctive shapes. The river mangrove propagules are up to 5cm long, pencil thick, slightly curved and have a pointed tip, while the grey mangrove develops a flattened, fleshy, ellipsoid propagule."

Mr Watt said that mangroves were once considered to be waste land and were treated as such; felled, filled, and dredged for coastal development.

"They were used as dumping grounds, suffered from pollution, and are particularly vulnerable to oil spills. The oil floats into the mangrove on high water and as the tide falls, the oil is stranded, smothering the pneumatophores, tree trunks and the animals living in the sediment."

"It has been estimated that 17 per cent of mangroves in Australia have been destroyed since European settlement. Once the mangroves have been removed, the exposed areas usually need to be protected by expensive artificial methods such as seawalls and other coastal infrastructure.

"More recently their true values are being recognised and are now considered to be some of the most biologically productive ecosystems in the world. Ironically and hardly surprising, they are also one of the most endangered ecosystems.

"They make an unparalleled contribution to the estuarine food chain and therefore the local economy, as well as providing several unsung ecosystem services. More than 70 species of fish have been recorded in the Australian mangroves.

"They provide shelter, breeding and feeding grounds for juvenile and adult fish, and it has been estimated that some 67 per cent of the entire NSW commercial and recreational fish catch are dependent for at least for part of their lifecycle on mangroves or associated habitat such as seagrass. beds."

The Australian mangroves provide roosting and feeding sites for an estimated 30 species of shorebirds many of which migrate annually over 10,000 kilometres to Siberia and Alaska, and points in between.

The Corlette foreshore.

The Corlette foreshore.

"Of these, 22 species of migratory birds and a further 10 residential species of shorebirds have been recorded on the shorelines of Port Stephens," Mr Watt said.

"Mangroves provide a myriad of ecosystem services for the socio-economic well-being of coastal communities protecting the shoreline from sustained damage. Their massive root systems provide a natural buffer against shoreline erosion, reducing and absorbing wave energy thereby protecting coastal areas from storm surge and preventing or reducing the risk of flooding of valuable agricultural land and populated areas. events.

"The root system also plays a crucial role in regulating water quality, filtering sediment and trapping pollutants before they can impact on the estuary and adjacent seagrass beds, ensuring clean water for the valuable oyster industry."

Mangroves are natural allies against the impacts of climate change on the coast. They are not only able to protect the shoreline from increased storm activity and sea level rise, but they are important carbon sinks, adds Mr Watt.

"They store carbon in the mud as organic compounds, locked away until disturbed by human intervention. It has been estimated that mangroves can sequester 2-4 times the amount of carbon than a mature forest, which primarily sequesters the carbon in the plants.

"Studies were conducted in 2010 and again in 2014 that demonstrated the value of mangroves for carbon sequestration, but the concept still seems to be struggling to gain any mainstream traction. Research has shown that there is a landward migration of mangroves threatening valuable saltmarsh habitat in the estuaries of south east Australia. It is unclear why these changes are occurring, which is concerning."