Oyster lovers on epic mission to restock Queensland bay

When Captain William Edwardson sailed north on orders from the NSW governor in 1822, he marvelled at the miles of oyster beds that greeted him in Moreton Bay.

But historic over-exploitation and coastal development means local populations are now functionally extinct.

In terms of water quality that's a very big deal given oysters work a bit like kidneys, filtering about a bathtub of water per adult, per day.

It's also a big deal for other marine life because oysters are habitat builders.

When they grow on top of and beside each other, their shells fuse into 3D structures that rise from the seabed, creating surfaces for new oysters to settle on and homes for everything from worms and other shellfish to crabs and fish.

So when there's been such a wholesale loss of such an important ecosystem, is there a way to bring it back? A tireless team of volunteers for restoration charity OzFish reckons there is.

And the science is quickly firming that they're onto something great that could one day help restore oysters across the whole bay and potentially elsewhere.

Semi-retired civil engineer Julian Balmer loves to spend his time off in a rather whiffy shed at the Port of Brisbane, making wire prisms and stuffing them with empty oyster shells recovered from restaurants and seafood traders.

He can't even guess at how many he and his mates have churned out over the past year but in total, there are now 6500 sitting at the bottom of the bay as part of an ambitious project to restore 100 hectares of shellfish reef.

Just another 43,500 or so and they'll be done.

"It does give you a warm, fuzzy feeling. Everyone's interested to know at the end of the day how many we've produced for the shift," Mr Balmer says.

Last time the gang got together they managed about 120, with break for a cuppa, cake and a chat. But usually it's 200 or more.

When the stockpile is big enough, in a few months time, another 2000 or so will be loaded onto a barge, chugged out to part of the bay controlled by the Port of Brisbane and chucked overboard.

Scientists are carefully monitoring what's going on in the depths and so far the chunky, triangular baskets designed by OzFish's Robbie Porter are doing exactly what they should - landing nicely on the bottom and providing much needed vertical habitat for a host of species.

Griffith University marine scientists recently analysed the types of animals making themselves at home on the degradable steel mesh so one day only cemented oyster shells will be left.

From nearly 4000 prisms, they found nearly three million new oysters had moved in with another 4.5 million other animals living among them.

Lead researcher Marina Richardson says ongoing monitoring is needed but it's early evidence the project should mature into a self-building system.

"They are showing very, very promising signs. We do need to continually monitor them but there's every sign at the moment that yes, is the way to go for restoration."

OzFish project manager Abbie Taylor says scientists from a number of universities have been involved in the project since its inception and for good reason.

If the approach is ever to be used inside marine parks like the one that covers almost all of Moreton Bay, authorities will need proof of its benefits.

That's why the University of Queensland is monitoring fish populations at the Port of Brisbane site, trying to firm up overseas estimates that every hectare of oyster reef can produce 2.2 tonnes of harvestable fish every year.

"We want to make sure this work is backed up, from every angle we can think of. We've got 100 more questions waiting to go for the scientists.

"We'll keep growing and growing to make sure that 'ok, well if it works like this in Moreton Bay, does it work like that in Gladstone, in Mackay?'"

At the Howard Smith Wharves restaurant precinct on Brisbane River, diners get through plenty of oysters every year.

But they may not realise the shells they leave are destined for the whiffy shed where Julian and his mates roll up their sleeves.

In the past year alone, just under four tonnes of shells were sent to OzFish.

Its CEO Luke Fraser loves the idea they'll soon be on the bottom of the bay, ready to support new life.

Meanwhile, back at the shed, volunteers with a wealth of life experience across many industries are constantly thinking about what next?

There have been invaluable refinements of late to the wire basket production line, resulting in a huge increase in production.

Thoughts have also turned to whether there might be a more time and cost-effective solution, and one is already being trialled in the bay and the Maroochy River on the Sunshine Coast.

Recycled oyster shells have been stuffed into a soft mesh manufactured overseas from sustainably sourced beech trees.

It's much lighter and easier to work with than steel - a bit like stuffing sausage skins, Julian says, and it will also disintegrate over time.

Now the wait is on to see if they prove popular with oysters and other critters. The results won't be known until year's end at the earliest.

Australian Associated Press