The endangered spiny seahorse has recolonised its former stronghold in Dorset due to the coronavirus lockdown, marine conservationists say.
During one regular survey dive at Studland Bay, the Seahorse Trust found 16 seahorses including pregnant males and a juvenile that had been born this year.
This is the largest number found in a single dive on the site since the charity began monitoring there in 2008.
Prior to this, a seahorse had not been seen at the site for two years.
“The ecology of the site has made a remarkable recovery,” he said.
“We have seen so many seahorses because the food chain has recovered, giving seahorses plenty of food to eat, and crucially, somewhere to hide.
“The seagrass has started to repair itself, and the spiny seahorses have taken advantage of this.”
Both of the UK’s native seahorse species – the spiny and the short snouted – were granted protected status in 2008 under the Wildlife and Countryside Act.
Mr Garrick-Maidment said: “The question is how we go forward.
“We do not want boats and divers banned, but the seahorses and seagrass do need their legal protection enforced.
“The 16 seahorses discovered on a single dive are an amazing discovery, but we now need the Marine Management Organisation (MMO) and Natural England to enforce the Wildlife and Countryside Act and the Marine Conservation Zone and put in place measures such as environmentally friendly moorings.
“The seahorses need protection to stop them being disturbed again as Covid restrictions are lifted, and to stop them vanishing from this legally protected site.
“We have a unique opportunity to help nature and to restore the balance of our planet.
“We must grab this with both hands, for the seagrass, for the sea, for humanity and crucially for these incredible seahorses.”
Natural England acts as a statutory adviser to the Marine Management Organisation, which is responsible for managing the site at Studland Bay.
Conservation advice for the protected marine habitats and species at the site is constantly being reviewed and will be updated if greater protection is needed, it said.
Matt Heard, Natural England area manager for Wessex, said: “We are firmly committed to protecting our precious habitats and wildlife and we are already consulting on updated conservation advice for the Studland Bay Marine Conservation Zone.
“We continue to work with the MMO and local groups to ensure the Marine Conservation Zone and its special wildlife are well managed, conserved and protected so that they can be enjoyed sustainably for generations to come.”
A spokeswoman for the MMO said both species of UK seahorses were “fully protected” under the Wildlife and Countryside Act 1981.
“Any activity that could potentially disturb seahorses requires a wildlife licence,” she said.
“Intentionally disturbing seahorses without a licence could lead to enforcement action.”