A box marked “special delivery” arrived about midday at Spurn Discovery Centre, on a remote East Yorkshire peninsula in the Humber estuary. It is unlikely the postal worker had any idea it contained 300,000 living oyster larvae – tiny pinprick-sized organisms destined to become part of a new oyster reef just off the English coast. Half a million native European flat oysters will be introduced to the estuary after being carefully nurtured by Wilder Humber, a partnership between Yorkshire Wildlife Trust, Lincolnshire Wildlife Trust and the green energy company Ørsted. The restoration project is the first of its kind in the UK and a key component in a desperate battle to restore Britain’s coastal waters to how they were before being blighted by overfishing and pollution. Globally, at least 85% of oyster habitat has been lost. Closer to home it is even worse. A map made in 1883 showed oyster beds skirting the British Isles with a thick belt in the Channel but now in Europe only an estimated 1% of native flat oysters remain. They were a cheap and easy food source going back at least as far as Roman times, indicated by the number of shells found in archaeological digs, with lots of Victorian writing mentioning the ubiquity of the bivalve. “Thinking about this history really ties people to the conservation,” said Kieran McCloskey, the marine restoration manager at Wilder Humber, adding that getting people to care about oysters was part of the challenge of restoration. In many estuaries, oyster beds were deliberately destroyed – at times with explosives – because they caused obstructions to ships. Pollution from groundwater runoff has also played a part, as has air pollution from fossil fuels. The Humber estuary is “one of the most important marine habitats in the region”, said Dr Boze Hancock, a senior marine restoration scientist on the global oceans programme at the environmental organisation the Nature Conservancy. It is unusual for a species to be categorised as “collapsed”, which is a classification more severe than endangered. This means, unlike in restoration schemes where nature can be relied upon to repopulate when left to its own devices, oysters will need to be physically reintroduced. “With a completely collapsed ecosystem in the UK, you have to put the biology back,” said Hancock. “It’s a case of reversing the process of fishing it out.” It is important because one adult oyster can filter 200 litres of water in a day and just one hectare of oyster reef supports three tonnes of other marine life every year. The oysters are grown in Aultbea, on the north-west coast of Scotland, by the Oyster Restoration Company especially for the project. They are gender-changing hermaphrodites “which doesn’t help the spawning process”, joked Rebecca Sheen from the company, which also provides oyster larvae to farms for the food industry. She said: “We’re creating a library of different genetic strains. For restoration, we’re looking for something hardy.” Under a microscope, the oyster larvae “look like little see-through clams”, McCloskey said. “They’re very cute.” Though European flat oysters are a slow-growing species compared with their Pacific counterpart, in 30 years the larvae introduced into the Humber this year could be the size of a dinner plate. If the method works in the Humber, which it has already done in the US and Australia, it is hoped it can be expanded to other sites, creating a network of oyster reefs that will join together. One perhaps unlikely target for the conservationists is offshore wind – beneath each wind turbine is metres of scour protection, boulders used to protect the base of the structure, which are excellent sites for oysters. “If we can pull this off,” said Hancock, “you can do this anywhere”.