The Great Barrier Reef might get the most attention, but it’s Australia’s shellfish reefs that are the country’s most threatened ecosystem.

According to a study led by The Nature Conservancy (TNC), since the mid-1800s more than 90% of the shellfish reefs off the nation’s coastlines have disappeared.  

They weren’t just ending up on someone’s plate – large numbers of oysters were harvested and burnt to create lime, which was used as an early form of concrete, and to pave roads.

The over-harvesting of oysters has had a big impact on our marine ecosystems. Not only do the reefs make great breeding grounds for fish and act as buffers to prevent shoreline erosion, they are also natural water filters.

“A single oyster can filter about 150 to 200L of water a day,” TNC Marine Manager Chris Gillies said.

“They remove algae and nutrients from the water; they eat what they want and spit the rest out. It’s four to five times more productive having an oyster ecosystem than a sandy ocean floor.”

Turning rubbish into reefs

The case of the disappearing oyster isn’t unique to Australia. Globally, 85% of reefs have been lost.

Luckily for the shellfish – and the world’s oceans – TNC has found a way to reintroduce oyster reefs and create less waste at the same time.

Working with restaurants and seafood markets, TNC collects used oyster shells that would otherwise end up in landfill. The shells are washed and left to bake in the sun for six months before being taken to a hatchery, where oyster larvae attach to them. More shells are placed on a bed of limestone in the ocean.

The oysters from the hatchery are then spread over the reef base, eventually turning into adults and spawning their own larvae, creating a vibrant reef.

TNC began restoring oyster reefs this way in the United States about 15 years ago. Its first Australian operation was in Victoria’s Port Phillip Bay in 2014, and it has since expanded to projects in Western Australia and South Australia.

Gillies said TNC will continue to supplement the Port Phillip Bay reef for another three years, until it is large enough to sustain itself, but that it had an impact almost from day one.

“Where the reefs were placed, it almost looked like a sandy desert you would see on land,” he said.

“The minute we put that hard reef structure back in, we started to see reef-associated species flocking to it, like certain types of urchins, crabs and fish. It really has attracted a lot of wildlife in a very short period of time.”

A low-cost wastewater treatment?

As well as rebuilding reefs, TNC is working with partners such as SUEZ to investigate potential industry applications for oyster reefs. For example, whether they could be used as a cost-effective solution to help filter wastewater or brine discharge.

“Industry are really critical partners and have a role to play in recovering the ecosystems,” Gillies said.

“That’s some of the science we’re testing – we know how to build the reefs, but do they make sense for wastewater?”

For SUEZ Director of Marketing, Communications and National Key Accounts Justin Frank, the oyster reef restoration project is “one of the most rewarding things I’ve ever worked on”.

The company has contributed financially to the project and also helps promote it. Frank said it made sense for the waste management and water solutions provider to get involved because it helps give back to the communities SUEZ serves, and is a great example of the circular economy in action.

“The project stops thousands of tonnes of oyster shells going into landfill and reuses them for a higher purpose … and helps to clean the water,” he said.

“It’s a full circular economy, which is what we’re trying to drive as a business globally.”

As a leader in resource recovery and water, Frank said SUEZ has a role to play in trying to do better things with the world’s resources.

“Only about 2% of the world’s surface water is actually drinkable, so if we don't do smarter, more circular things with water, there’s going to be big problem in the future,” he said.

“And on the waste recovery side, we have to start treating waste streams as resources.”

SUEZ is proud to be a Principal Sponsor and exhibiting at Ozwater’19 in May. To learn more and to register, click here.