Millions of tiny engineers help to restore health of marine ecosystem in WA

Beneath the peaceful surface of Cockburn Sound (Derbal Nara), south of Perth, millions of tiny marine engineers are hard at work.

A project is harnessing the remarkable abilities of the humble mussel to help restore the health of the sound.

Cockburn Sound was once home to a thriving mussel farming industry that aquaculturalist Glenn Dibbin worked in for nearly four decades.

Over that time he witnessed a "rollercoaster of a boom-bust cycle in regard to seafood and fish life". As commercial mussel farming declined and operators closed or relocated, much of the infrastructure was left idle.

Today some of that infrastructure is being given a new purpose by the Byssal project, which reimagines mussel farming for ecosystem restoration rather than seafood.

The project was founded by Mr Dibbin alongside Recfishwest, representing the interests of WA recreational fishers, as well as industry partners Indo-Pacific Environmental and Commercial Maritime.

Nature's water filters

Mussels, like most bivalves, are filter feeders that draw water through their gills, extracting microscopic food particles and, in the process, improving water clarity.

"An adult mussel can filter up to three litres of water an hour," Mr Dibbin said.

"So when we talk about 1,000 tonnes [of mussels], when we start doing those numbers, the zeros … you can't use a calculator, there's so many zeros."

According to Recfishwest, nearly 80 per cent of the Cockburn Sound's seagrass meadows have been lost since the 1960s.

In addition to providing critical habitat, seagrass meadows also stabilise sediments and store vast amounts of carbon from the atmosphere.

According to Mr Dibbin, murky water is a key factor in the loss of the area's seagrass.

"The sunlight penetration couldn't get down into the deeper waters, because there's so much activity above them … so mussels, by filtering the water, clean that water so it actually gets a lot clearer to allow seagrass potential recovery," he said.

Mussel farms also provide habitat and food to a wide range of species.

Compared to many marine environmental restoration projects, Byssal's set-up is relatively simple, with sturdy 10-metre lengths of hairy rope suspended from buoys just beneath the water's surface.

Baby mussels (spat) naturally present in Cockburn Sound attach to the rope of their own accord and, over time, the ropes become densely covered in mussels, forming long, reef-like structures.

As the mussels mature, they become the foundation for an increasingly complex ecosystem.

Seaweeds colonise their shells, creating habitat for juvenile crabs, prawns and shrimp, which in turn attract larger predators such as squid and fish.

"At the end of the day, it becomes a massive nursery area for the ecosystem," Mr Dibbin said.

Feeding the food web

Cockburn Sound is also home to the largest spawning aggregations of pink snapper in Western Australia. Mr Dibbin said for years these fish had been feeding on mussels, affecting the viability of mussel farming.

During spawning periods, the snapper "were eating up to about 25 tonnes a night", he said.

But today, Mr Dibbin said, those same fish had become part of the project's success.

After decades trying to stop snapper eating his crop, Mr Dibbin now hopes they will turn up.

Recfishwest chief executive Andrew Rowland said a successful rollout of the Byssal project had the potential to translate to better fishing.

"We need to underpin the environment and the productivity, which supports healthy fish stocks and it all starts at that baseline productivity," Dr Rowland said.

He also emphasised the vital role that community would play in Byssal's future.

"Projects like this are only successful when people get behind it, when they understand the benefits and they talk about it at their fishing clubs, or with their local politicians, or at the pub," he said.

Dr Rowland said the next stage would be to scale the operation up.

"We'd like to see a thousand tonnes of mussel production every year to continue to build on what we've started here," he said.

Expanding restoration through 'greenwalling'

The Byssal project is also helping to establish mussel populations in other locations through a process known as greenwalling, which involves mussels of a suitable size being removed from the ropes and reseeded onto nearby rock walls.

In collaboration with the Fremantle Ports Authority (FPA) and DevelopmentWA, Byssal has recently completed the first round of mussel reseeding along limestone walls within the Australian Marine Complex at nearby Henderson.

FPA environment manager Rebecca James said the project was "a nature-based solution to how we can continue operating ports … in sustainable ways".

"Ports have a lot of infrastructure … if we're able to lean into that, so that infrastructure is then supporting the health of the ecosystems in which we're operating, it's really beneficial," she said.

Ms James said initiatives such as Byssal were a way of building environmental resilience.

"If shocks do happen, like heat waves, [the marine ecosystems] are much more likely to be able to respond to that and not have such devastating events," she said.

"It's in everybody's interest to look for these solutions and embrace and be a part of them."