Victoria's biggest-ever reef restoration project is underway, in attempt to restore the once-abundant populations of native oysters in Port Philip Bay.

One hundred and 80 tonnes of limestone have been deployed at Margaret's Reef, near St Kilda, and Wilsons Spit, near Geelong, which will encourage 300,000 native Angasi oyster hatchlings to flourish there.

Fisheries Victoria, the Albert Park Yachting and Angling Club and the Nature Conservancy have partnered to create the shellfish reefs.

Simon Branigan, marine restoration coordinator for the Nature Conservancy, said these areas which were once vibrant, functioning ecosystems were now largely inactive.

Overfishing and damage to the original reefs meant the native oyster populations there had plummeted.

"The key lesson learnt is that for the oysters and mussels to survive, they need to be elevated, off the seabed for survival and growth," Mr Branigan said.

A shellfish restoration test plot at Margaret's Reef in 2016. ( Supplied: Simon Branigan )

Filtering a bathtub of water a day

Mr Branigan explained that native oyster populations played a number of important roles within the local ecosystem.

"They provide really important habitats for a number of fish species," he said.

"Oysters are also filter feeders, so they are extremely efficient at filtering the water.

"One oyster can filter up to a bath tub of water a day, so imagine thousands, if not millions, of oysters in a bay providing that type of service."

Oysters once abundant in Port Philip Bay

Mr Branigan said when Europeans first settled in Melbourne they were overwhelmed by the bounty of native Angasi oysters.

Native Angasi oysters were once abundant in Port Philip Bay. ( Supplied: Nature Conservancy Australia )

"When Flinders first sailed through the heads in Port Philip Bay, he noted in his diary how prominent the shellfish reefs were and how they were a navigational hazard," he said.

"And when the Europeans first settled in Melbourne, they loved oysters so they would go out in sail boats with these dredge cutters that would be dragged behind ... and collect the oysters."

Mr Branigan said that oysters were eaten locally in bars or bottled and exported, while the shells were used in building.

"They would crush them and use them for lime," he said.

"A lot of the old buildings in Melbourne would be made out of the remnant shellfish reefs in the bay.



"Very similar to the gold rush, but except for gold, it was oysters."

And long before European settlement, Mr Branigan said that the local traditional owners sustainably harvested these reefs for thousands of years.

He said that the principal aim of the current reef restoration project was to restore habitats to benefit biodiversity and other ecosystems, like water quality, in Port Philip Bay.