Seahorses off the Dorset coast have been highlighted as some of the creatures making a comeback with the help of conservation action, the Wildlife Trusts has said.

It has also been a good year for sightings of marine wildlife as thousands of volunteers helped survey shores around the country to gather information and monitor marine protected areas, a review of the year by the Trusts has found.

Conservation successes include Dorset Wildlife Trust's work with fishermen in Poole Harbour, who have both Marine Stewardship Council and Responsible Fishing Scheme accreditation for sustainable management of the sea, which is helping seahorses.

As part of the scheme, Dorset fishermen have been reporting their marine sightings and have been finding the extremely rare short-snouted seahorse off the Purbeck coast.

Both the short-snouted seahorse and the spiny seahorse are native to Dorset. Seahorses face multiple threats from trawlers that scour the sea bed and from yacht anchors – so good management is essential to the survival of these legally protected creatures, the Trust said.

While the short-snouted seahorse is found in rocky and gravelly areas, the spiny seahorse is more likely to be found in underwater meadows, hiding in seagrass. Dorset Wildlife Trust hopes Studland Bay which has a seahorse colony will be designated as a Marine Conservation Zone in 2019. DWT helped introduce a world first in seafood labelling by working with fishermen to demonstrate responsible standards whilst caring for the marine environment in Poole Harbour. The double award of MSC & RFS is a global first for the Poole Harbour clam and cockle fishery.

Meanwhile, it has been a bumper year for nudibranch, or sea slugs, according to several Wildlife Trusts, and a good autumn for sightings of curled octopus by divers.

But there was bad news too for marine wildlife, with sewage spills and storm drains dumping wet wipes and sanitary products onto beaches, while plastic pollution continues to be a major problem. Beach cleans took tonnes of litter off the shoreline.

Dr Lissa Batey, senior living seas officer at The Wildlife Trusts, said: "This review of sightings and action from across the UK has given a glimpse, a mere taster, of the wonders of our marine wildlife – delightful species that everyone has the opportunity to encounter and learn more about.

"But it has also shown us the problems that remain and the challenges that our sea life faces.

"It's not too late. We are already seeing recovery in some of our marine protected areas, but we don't yet have a fully functioning network of nature reserves at sea, where wildlife has the opportunity to thrive.

"That's why we are looking forward to the third designation of marine conservation zones in 2019 - with these we would have the potential to reverse current marine wildlife declines."