Millions of native oysters are to be put into the Solent, once the site of Europe’s largest oyster fishery.

The five-year project aims first to restore a thriving oyster population to the waters between the south coast and Isle of Wight. Oyster beds provide habitat for many other species and the shellfish filter vast volumes of water – 200 litres per oyster – helping to clean up pollution. Once re-established, significant oyster fishing could resume.

“We hope this programme will have a transformational effect on the Solent in the long-term,” said Tim Glover, at the Blue Marine Foundation, which is leading the project. A million young oysters will be put into the Solent in 2017, in places where they cannot be legally fished. A further 10,000 are being put in special cages in harbours, from where they can send out larvae.

“It’s a really great project and it could have a phenomenal impact,” said Jo Preston, a marine biologist at the University of Portsmouth who is monitoring the project. “Without a helping hand it is very unlikely the oysters are going to get going again.”

Oysters have been fished in the UK since at least Roman times and at its peak in the 1920s 40 million oysters were eaten each year, with the abundance leading to the mollusc being known as a poor man’s food. But by the 1960s this had fallen to 3 million oysters a year.

The population in the Solent crashed again recently, with the annual catch falling from 200 tonnes in 2007 to just 20 tonnes in 2011 – about 250,000 shells – and oyster fishing was banned in the Solent in 2013. “It’s a perfect storm of overfishing, habitat destruction, dredging, climate change, disease, invasive species and quite possibly pollution,” said Preston.

One key problem is the American slipper limpet, which has taken over the oysters’ habitat as they have declined and now dominates. A switch back to oyster beds is needed for the overall health of the marine ecosystem, said Preston: “The biodiversity associated with the native oyster is far greater than that associated with the slipper limpet. It’s also brilliant for other fisheries as it becomes a refuge for juvenile fish and lots of other things grow on top of oysters.”

Aerial view of the Solent strait between the Isle of Wight and the south coast of England. Photograph: Peter Barritt/Robert Harding

Oyster restoration projects are taking place around the UK, particularly in Essex and parts of Scotland and Wales. But the Solent project is one of the biggest and the first to use cages, provided by the MDL Marinas company. These hang from harbours and protect the oysters, which can then reproduce and send a “massive input of larvae into the Solent”, according to Preston.

The cages have been tested over the last year, with some success in Portsmouth harbour. “I thought they were all going to die – I mean, it’s filthy there,” said Preston. “But we had only 7% mortality – I was astonished.” However, another test cage in Langton harbour was all but wiped out due to a toxic algal bloom, possibly connected to sewage overflows after storms.

The project costs about £250,000 per year, funded by charitable donations, and will use commercial hatcheries to grow up the oysters to about 5cm before being released. “By the end of five years we hope we will have done our ground work to make sure the oysters are installed again,” said Glover. “But it is probably five to 10 years before we see a real, thriving oyster stock in the Solent.”

Preston is optimistic that a significant oyster fishery could return in the future. “Absolutely, if they don’t open it up too fast and too soon, and as long as there are protected grounds where they are not fished, then I think there is every hope of a robust fishery,” she said.

Most oysters eaten in the UK today are farmed Pacific oysters. Their flesh is less firm than the native oyster and many people prefer the flavour of the natives. “They are quite different,” said Glover.