Navy turns to oysters to battle the pollution of Portsmouth

It could be Britain’s bleakest site for a nature restoration project. Ferry-bound petrol tankers wait in one direction, two aircraft carriers float in another, while the north offers a vista of a barbed wire fence encircling a navy base. Below are the polluted waters of Portsmouth Harbour.
Yet this jetty on Whale Island is home to a scheme hoping to grow native oysters and improve water quality. It is believed to be the Ministry of Defence’s first marine conservation project.
Rod Jones, assistant head of environmental protection in Navy Command, has the glamorous job of scrubbing off the algae that has attached itself to the cages the oysters are being grown in next to the jetty. His colleague Harriet Rushton, a marine biologist, is busy with two trays of water, washing the oysters that endure the sediment-heavy waters here.
The Solent used to be the UK’s biggest native oyster fishery, but it collapsed last century under pressure from overfishing and pollution. Jones and Rushton do not pretend they can single-handedly reverse the situation, but plan to rear thousands of European flat oysters (Ostrea edulis) for release into nearby Langstone Harbour and the River Hamble.
“The native oyster is what we call a keystone species. When they grow they form reefs, which then other species can colonise. You just get so much more bang for your buck,” said Rushton, who is excited about the prospect of fish, sea squirts and sea sponges flocking to the reefs the oysters should build.
Typically, such a project would use adult oysters sent from relatively pristine locations such as Scottish lochs. But the Solent’s waters suffer a cocktail of chemicals from Portsmouth Harbour, as well as a sewage works that has triggered fines for releasing raw sewage into Langstone Harbour.
Rushton’s answer is to grow young oysters in the dirty waters to make them more robust and better adapted to their future environment. “It’s early days but they might have a better chance of survival,” she said.
Her first efforts last year saw about 200 of 2,000 oysters survive, but she said a 90 per cent mortality rate was fairly typical. She partly blames a warm June last year, which was the hottest on record.
“This year they’re doing much better,” said Rushton, an environmental manager at the MoD arm Defence Equipment and Support. It looks like 400 of 2,000 will survive. Small changes have been made, such as putting the cages next to pontoons rather than under them.
Should the oysters manage to thrive despite the odds, they could improve the Solent’s water quality by filtering sediment, algae and nutrient pollution. They can also play a small role in tackling climate change, by locking away carbon in the calcium carbonate that forms their shells.
“The question is: can it help improve the water quality, which has gone past a tipping point? There might be a time when the water starts improving again, when everything comes back: seagrass, fish,” said Alex Ford, professor of biology at the University of Portsmouth, who is not involved in the scheme.
Rushton hopes there could one day be enough native oysters to return to commercial harvesting of the shellfish. But she cautioned that it is a long way off — establishing reefs with enough oysters could take a decade or more.
For Jones, success would simply be about proof of concept. “Hopefully this will prove that there is benefit, in this hard landscape, this industrial waterfront. That you can do something to improve the marine environment even in a small way. The biggest outcome would be to show things can be done,” he said.