For the past 18 months, the so-called "storm squad" has been tasked with collecting shoots of the posidonia plant that are pulled from the seabed during wild weather. The posidonia is an endangered seagrass that thrives in sheltered bays and provides a safe habitat for juvenile species.

But the posidonia is in desperate need of a safe habitat itself, with traditional block-and-chain boat moorings, winds and current changes scarring the marine floor and threatening the slow-growing plant's survival. Posidonia's roots are often detached from the sea floor during storms, with shoots washing ashore.

A team of "underwater gardeners" led by marine ecologist Associate Professor Adriana Vergés from the University of NSW, will this week don their scuba gear and embark on a bold mission at Shoal Bay to replant 1500 of those seagrass shoots, diligently collected by volunteers and stored in submerged stations.

"Posidonia australis is a slow-growing seagrass that likes to live in the same beautiful sheltered bays where us humans like to live, build our houses and moor our boats, so the building of marinas, coastal development, pollution and dredging has caused its decline," Associate Professor Vergés said.

"Without seagrasses, a lot of emblematic species like seahorses, as well as many species we like to eat, such as blue swimmer crabs, cuttlefish and snapper, would decline from our estuaries."

Associate Professor Vergés is leading a team of scientists in Operation Posidonia, which aims to restore seagrass where it is endangered as well as replace traditional swing moorings with environmentally-friendly ones, known as EFMs.

She said Shoal Bay was the ideal test site for the operation because of the high number of naturally-detached shoots available to be replanted, and because conditions meant the replanted posidonia had a good chance of survival.

The scientists use jute mats to stabilise sediment in old mooring scars, which helps with the replanting. About 70 per cent of the first shoots planted in an earlier mission survived.

"Now, nine months after the initial restoration we're starting to see growth from the shoots that we planted; we've even seen flowers so it's encouraging," Associate Professor Vergés said.

"Having said this, every estuary is going to be a bit different. For example, Sydney Harbour is going to be tough to restore, because there's very, very little posidonia left and there are multiple stressors like boats and ferries.

"So, it's likely that we will be more successful in some estuaries and less successful in others, but where there's a will there's a way."

Four trial EFMs were installed by the Roads and Maritime Service in Shoal Bay about a month ago, Associate Professor Vergés said. Between Wednesday and Friday this week, scientists will be replanting the shoots around those new EFMs.

The next stage of the project, a collaboration between UNSW Sydney, the Sydney Institute of Marine Sciences, the NSW Department of Primary Industries - Fisheries and The University of Western Australia, is a roll out in an endangered estuary.

Associate Professor Vergés is drafting grant applications to raise funds to take the project to Lake Macquarie, but she said scaling up the project to restore the seagrass to six endangered estuaries was at least a decade away.

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