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Mangroves killed during Black Summer bushfires near Batemans Bay are not growing back

Simon Rowe checks trees that boiled alive during the Black Summer bushfires, some of which were up to 300 years old. (ABC News: Holly Tregenza)

At a curve on the Clyde River known as Chinamans Point, the lush green tops of eucalyptus trees poke out from behind the mangrove forests that line the bank.

The bush has largely bounced back from the catastrophic Black Summer Bushfires of 2019/20.

But the mangrove trees sitting inside the tidal zone have remained ghostly white. Most are dead and showing no signs of coming back.

"About 90 per cent of what you can see here is just completely dead," says Simon Rowe, a program manager-environment from not-for-profit group OceanWatch.

"It's a scenario we haven't seen before."

Mangroves killed during Black Summer bushfires aren't growing back(Supplied: OceanWatch)

How a forest on water dies in a fire

Mangroves burning during bushfires is not a new phenomenon.

What is different about this is that they are not recovering.

James Cook University mangrove ecologist Norm Duke says it is exceedingly uncommon.

"On the severity and scale of the damage, there's been nothing like it before," Professor Duke says.

While some of the mangroves did burn physically, most were killed by radiant heat.

"I've seen the mangroves with blisters, like a burn on your skin.

Claudia Santori from OceanWatch checks on a new seedling, one of the few that have sprouted since the fires came through. (ABC News: Holly Tregenza)

OceanWatch has been commissioned to track the decline of the mangroves near Batemans Bay.

Project officer Dr Claudia Santori says when a local oyster farm first raised the alarm about state of the mangroves, she thought it sounded impossible.

"We couldn't believe our eyes," she says.

"They're normally green, lush, noisy, vibrant environments. Now they're skeletons, these white, dying trees."

Oyster farmers sound the alarm

Some of the mangroves killed during the fire were upwards of 300 years old.

"It's going to take several decades for them to come back," Professor Duke says.

But oyster farmers along the Clyde and the animals that rely on the mangroves to survive might not be able to wait that long.

Mangroves roots hold together mud and sediment, reducing coastal erosion and maintaining the quality of the water.

They also clean the river, keeping debris from travelling downstream.

When they die, the sediment is free to flow back into the river.

"All the mud that these trees are holding together will flow into the estuary, which will create turbidity and can affect fish and the local oyster farming," Dr Santori says.

Clyde River oyster farmer Kevin McAsh has been looking after mangrove seedlings as part of the restoration attempt. (ABC News: Holly Tregenza)

Kevin McAsh has been an oyster farmer on the Clyde for more than 15 years and was the first to raise the alarm about the dead mangroves.

He is worried about the impact on the river system if they fail to grow back.

"They catch a lot of rubbish that comes down the river when the rain comes, and they also hold back sediment and erosion," he says.

Rescue attempts underway

Late last year OceanWatch, Landcare volunteers and oyster farmers began measuring the damage to mangroves.

They are trying to help them regrow by gathering seedlings that are caught up in oyster farming infrastructure, caring for them in a nursery and replanting them at the burnt sites.

Mr Rowe is part of a team planting seedlings to encourage regrowth in the dead mangrove forests. (ABC News: Holly Tregenza)

"There is some hope. This last summer, we saw a handful of seedlings establish," Dr Santori says.

Professor Duke says this kind of intervention is rare in mangroves, which normally bounce back well on their own.

He is worried not enough will be able to be achieved before the next big bushfire comes through.

"If that occurs, and we're back in another cycle of intense heat and dryness, are we to expect another fire season like the last one?

"That would be devastating."

Mr McAsh knows it will take decades to restore the mangroves, but he does not see any other option but to try.

"We're not going to bring the mangroves any faster, but if we don't do anything, they won't ever come back," he says.

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