Restored Solent seagrass meadows show fivefold rise in juvenile fish, study finds

Three years ago, volunteers in waders dropped 40,000 small hessian bags filled with sand and seagrass seed into the shallow waters off the Hampshire coast, and were told it might be a decade before anyone knew if it had worked. On Friday, scientists said the evidence was in: the restored meadows now support five times as many juvenile fish as neighbouring bare seabed, and are spreading on their own.

The findings, from a three-year monitoring programme led by the Hamble Marine Laboratory and published in a peer-reviewed marine ecology journal, are the most detailed assessment yet of a seagrass restoration project in UK waters. They come as the government weighs whether to fund a national expansion of such schemes as part of its coastal carbon targets.

“The seagrass has done what we hoped and then some,” said Dr Owen Ferris, the laboratory’s lead ecologist. “We have juvenile bass, black bream, two species of pipefish and more cuttlefish eggs than we can count, in a place that three years ago was essentially an underwater car park. The meadows have expanded by about 30% beyond where we planted them. They are self-sustaining.”

Seagrass, a flowering plant that grows in sheltered shallows, was once common around the British coast but has declined by an estimated 90% in the past century as a result of pollution, dredging, boat moorings and disease. The meadows matter disproportionately: they store carbon in their roots and sediment at rates that rival tropical forests, they damp wave energy and they shelter the young of commercially important fish.

The Solent project, which cost around £900,000 and was funded by a mix of environmental grants and a port operator’s mitigation payments, planted 3.5 hectares across four sites between Lymington and Calshot. The team used a method pioneered in Wales in which seed is sealed into small biodegradable bags that sink, rot and release their contents into the sediment, avoiding the labour of planting by hand. Survival rates at three of the four sites exceeded 60%; the fourth, exposed to heavier boat traffic, was largely lost.

Not everyone is persuaded that restoration can be scaled. Prof Angela Rutter, a marine conservation specialist not involved in the study, said the Solent results were “genuinely encouraging” but warned that seagrass remained vulnerable to the pressures that destroyed it in the first place. “You cannot plant your way out of poor water quality,” she said. “The Solent has had serious investment in sewage treatment. Many estuaries have not.”

Ferris agreed. “Restoration is the second step,” he said. “The first is to stop killing it.” The laboratory is now seeking funding to extend the project to 20 hectares by 2029, which would make it the largest in northern Europe.