In short:
Oyster reefs filter water and provide habitat for fish and other sea creatures.
The "deployment" was the largest undertaken by the Moreton Bay-based restoration project.
What's next?
Current law limits reef restoration in the marine park, but project organisers hope new legislation will allow them to expand.
More than 3,000 man-made oyster reefs have been dropped in Moreton Bay as part of an effort to bring shellfish back into the ecosystem.
Marine scientist Marina Richardson from Griffith University said oysters are the "kidneys of the sea", filtering excess nutrients and pollutants from the water and providing habitat for fish, invertebrates and other creatures.
Dr Richardson said oysters, once widespread, are "functionally extinct" in the bay, but there is hope they can be brought back.
Volunteers from the not-for-profit Ozfish set out on weekly missions to collect oyster shells from large restaurants and shuckers around Brisbane, bringing roughly four tonnes of shell back to Ozfish headquarters at the Port of Brisbane every week.
The shells sit there for at least four months, sanitised by sunlight, before they are put through an industrial-sized sift shaker, tumble washed, and put into metal cages known as Robust Oyster Baskets, or ROBs.
Volunteers building Robust Oyster Baskets (ROBs). (Supplied)
From there, they are loaded onto a barge and "deployed" into a 19 hectare stretch of sea controlled by the port, where oyster larvae — or spat — land on the shells.
If all goes to plan, by the time the wire rusts away, the oysters will have fused into a self-contained reef.
Robbie Porter, one of the few Ozfish employees, started the shellfish restoration project seven years ago.
He said this deployment is the largest the project has undertaken and brings the total number of ROBs dropped to more than 14,000.
He said even before the cages develop into full-blown reefs, they provide plenty of "nooks and hidey holes" for animals like prawns, worms and crabs.
More than 3,000 man-made oyster reefs were dropped in Port of Brisbane waters. (Supplied)
Ozfish has teamed up with academics, including Dr Richardson, to track their success.
A survey done by Griffith University found each ROB was attracting around 3,000 shellfish and other critters.
University of Queensland research shows each basket can filter around 120 litres of water an hour after a year-and-a-half in the bay.
Restoring the bay
Dr Richardson said the shells used by the project are the ideal "hard substrate" oyster spat needs to land on and grow.
"There are chemical cues that are omitted from those shells which act as navigation cues for spat," she said.
Dr Richardson said oysters, once widespread, are "functionally extinct" in the bay. (Supplied)
Further, she said the caging technique means oysters will grow together and avoid becoming washed into less than ideal conditions.
"I think they really hit the nail on the head with their design," she said.
While oyster reefs once spread across the bay, more than a century of colonial and industrial change has taken out 95 per cent of what was there.
Despite that, restoration projects are not allowed in the Moreton Bay Marine Park.
This week's deployment was the largest yet for Ozfish. (Supplied)
Mr Porter said his organisation would love to work outside of the 19 hectare plot and is "working closely with marine parks on legislation to make that happen".
Dr Richardson said while plenty is known about where oyster reefs were historically, there is a lack of research about where and how oysters can be a part of the bay's future.
"Areas where there was previously oysters might not be suitable anymore … it's really important we find out where the oysters are now," she said.
Wire baskets full of oyster shells will form reefs on the bed of the bay. (Supplied)
A spokesperson from the Department of the Environment, Tourism, Science and Innovation said "shellfish reefs have the potential to play an important role in inshore marine ecosystems" and the department is "committed to ensuring attempts to rehabilitate shellfish reefs succeed without compromising other marine values".
They said they are working on an "operational policy to inform decision making" and "tools that will help to improve the success of shellfish reef rehabilitation projects", which are expected to be complete in 2025.
The project has dropped more than 14,000 ROBs into the water at the port. (Supplied)