Millions of mussels rejected from supermarket supply are being used to help boost water quality and marine life in Auckland's Hauraki Gulf.

Over the last two weeks, the Mussel Reef Restoration Trust has seeded about 3.5 million live adult mussels across an area the size of eight rugby fields.

The drops are part of the trust's flagship project Revive Our Gulf, which the trust says is the world's first attempt to restore green-lipped mussel reefs. It follows a successful trial earlier in the year.

Photographs provided by the trust show the effect of its mussel bed restoration trial. Photo / Supplied
Photographs provided by the trust show the effect of its mussel bed restoration trial. Photo / Supplied

Mussel beds once covered vast swathes of the Firth of Thames and Tamaki Strait but were ripped up by commercial fishing boats and poachers, with the fishery eventually collapsing in the 1960s.

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Mussel farming on ropes took over as a way to meet market demand but the trust says the loss of the mussel beds left the gulf's waters murky, inhospitable to other marine life and vulnerable to land run-off.

Mussel Reef Restoration Trust chairman John Laurence described the reefs as "magic carpets", with a single mussel able to filter up to 350 litres of seawater each day.

"These magic carpets filter sediments from the water and provide rich habitat for juvenile snapper and other marine life."

He said that a partnership with North Island Mussels had made it possible to make two drops of 30-40 tonnes of mussels over the last two weeks and that more drops were expected.

The mussels, which did not meet size requirements for supermarket supply, were provided free of charge, with the trust covering the cost of transport to the restoration area to the east of Waiheke Island.

Mr Laurence said the trust's vision was to work with mussel producers throughout the year.

It is also supporting Ngati Whatua Orakei's mussel bed restoration project in Okahu Bay.

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