Restoring Australia’s lost shellfish reefs to reshape a vast underwater kingdom

Several nautical miles offshore, a special diving boat is a mere speck in Port Phillip Bay. 

The bay, comprising almost 2,000 square kilometres, fans southwards from Melbourne, Australia’s second-biggest city.

Two divers carrying live shellfish are descending on an artificial reef, taking another small step in an ambitious reef restoration project — the largest yet undertaken in Australia.

Known as Reef Builder, it is backed by federal and state governments and overseen by The Nature Conservancy.

“Our Commonwealth investment has produced 40 hectares of shellfish reefs, and it’s a truly fantastic program,” Environment Minister Sussan Ley said.

Artificial reef restoration

Shellfish reefs were once prominent around much of the Australian coastline.

Reef Builder is restoring marine habitats from Noosa in Queensland to Perth in Western Australia.

In 2017, Port Phillip became the first of many planned future projects.

Mr Reeves has been heavily involved in the labour-intensive and tricky work.

Once a site for a reef is identified, a large barge is used to bring in huge limestone blocks that are lifted by a crane and dropped overboard.

Within months they will become, quite literally, the building blocks of life.

Divers then disperse juvenile shellfish onto the new reef site in a process called seeding.

The tiny oysters attached themselves to scallop or oyster shells that have been salvaged from seafood wholesalers and restaurants, part of a recycling initiative called Shuck Don’t Chuck.

Breeding hatchlings

The young oysters and mussels are grown at the Queenscliff Shellfish Hatchery, a state government-run facility on the western side of Port Phillip.

The restoration project has been producing the angasi or native oyster, sometimes called the flat or mud oyster.

Port Phillip Bay was once teeming with them, but in Melbourne’s early days they were an all-too-convenient food source and the shellfish reefs were a nuisance to marine navigation.

Oyster shells also provided the lime crucial to building the city’s grand colonial buildings. Within decades the shellfish reefs were overfished or dredged to oblivion.

By the 1960s, dredging for scallops in the bay further reduced the population of angasi and blue mussels — it means the shellfish hatchery is crucial to the restoration project.

“This is really the linchpin of the restoration operation,” Mr Branigan said.

The scientists have had to discover much about the little-known and cryptic angasi oyster.

Unlike the more common Sydney rock oyster, it broods its young internally and then, when conditions are suitable, releases them into the water.

“We started off with very little success; we maybe got 300,000 out there in the initial stages,” hatchery manager Kim Weston said.

An ambitious goal

Twelve hectares of artificial reefs have been constructed in Port Phillip — the ultimate aim is an ambitious 100 hectares.

Even if that is achieved, it will only represent a 10th of what was there at the time of European settlement.

Rebuilding these underwater kingdoms is paying dividends; six years into the project and recreational anglers are catching legal-sized whiting and other species that were previously hard to find.

But Bob Pearce from the Albert Park Yachting and Angling Club, which has been instrumental in the reef rebuild, believed there was more at stake than simply catching a feed of fish.

Marine scientists Simon Branigan and Simon Reeves are seeing a greater diversity of marine life every time they visit the reef sites.

With an estimated 80 per cent of shellfish reefs lost worldwide — Mr Reeves believed the restoration of Port Phillip’s reefs had come in the nick of time.

Watch this story on ABC TV’s Landline at 12:30pm on Sunday, or on ABC iview.