Could mangroves save Victoria’s second largest bay?

Local volunteers are currently trialling a nature-based solution to rising sea levels at Western Port Bay.

While many coastal towns have relied on seawalls to counter sea level rise, the Western Port Seagrass Partnership (WPSP) have implemented a mangrove rejuvenation program.

The volunteer organisation was established in 2002 by climate science experts and community members, who say they were forced to pursue this novel approach due to a lack of government support.

“Mangroves are cheap to grow and the State, up until now, has not put any effort into stopping that erosion and it’s eroding about a metre a year,” says WPSP Board member Hugh Kirkman.

Although mangroves have been successfully planted in tropical climates, this has never been done before in Victoria.

Mangroves are generally seen as habitats for birds and small fish, but WPSP Director Ian Stevenson, hopes that they will also act as a barrier to the erosion and inundation that has plagued Western Port since the 1970s.

“Locals started experiencing major flooding sessions throughout the area in the 1970s, which destroyed the seagrass on the eastern arm of Western Port,” says Stevenson.

“The inundation is largely from storm surges, which have always occurred, but they’ve been continuing in recent decades to the point that inundation and flooding is quite frequent,” according to Stevenson.

The worst affected areas are rural land (particularly an old swamp) in Lang Lang and the more urban area of Grantville- which has suffered continuous erosion and inundation that is eating into the front yards of private properties despite the presence of a protective concrete seawall.

In one extreme case, the front paddock of a farmer’s property suffered over a kilometre of inundation after a major storm.

Some farmers have therefore taken desperate measures to protect the area, dumping car bodies, rocks and concrete, in front of the shore.

It is hoped that mangroves will provide a cost-effective alternative.

“If the mangroves can arrest erosion, and we can reduce sediment around those areas, then we’ll overcome some of the problems of inundation as well as avoiding some of the cliff erosions,” Stevenson explains.

Kirkman says that if the program is successful it would be a significant environmental breakthrough because “[mangroves] can hold and store carbon dioxide about ten times better than a rainforest. Sometimes it has been recorded as more than ten times, but no less than that.”

The organisation is still perfecting a number of techniques, including how far apart seeds should be planted, how many rows should be put in and how far out to sea they should go.

“We’ve been trying a whole range of experimental techniques for ten years on propagating, seed collection, direct seeding, and putting pipes in for protection,” Stevenson says.

Currently, the process involves taking seeds off the tree once they’ve germinated, and putting them in a nursery within a glass house. Once they have grown, they are placed in a 10 mm plastic pipe, pushed in the ground, and grown from there.

The WPSP’s activism and ability to adapt to the challenges of climate change despite their limited resources, is an encouraging and unusual development, according to according to Swinburne University’s Dr Belinda Christie.

“It’s usually more of a case of government or council intervention rather than local people going ‘hey we’re a bit worried that in 50 years’ time our walkway is going to be under the water’. I haven’t heard many cases of grass roots intervention,” she says.

Although their ambitious new approach shows promise, Kirkman admits that they still don’t know if it will actually work.

It has been a long and sometimes frustrating process as the seeds can sometimes get full of seagrass or stuck on the edge of the pipe.

“We’ve lost a lot of them [the plants] but I suppose the best germination we’ve had is about 60%, sometimes we get 8% or 30% or something like that,” says Kirkman.

“It’s still early days. We’re having some success, but it’s still just the start of the bigger issue and on its own it’s unlikely to be successful for that section of coastline,” Stevenson says.

“We’ve got some plants that are about 10 years old that are doing very well. We’ve had a lot of failures because of the terrain, but there are plenty of areas where we’ve seen natural re-vegetation.”

For now, the experiment continues.

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