One of the largest seagrass beds in the UK, home to seahorses, pipefish and scallops and a highly effective carbon sink, has been identified off the south coast of Cornwall.
An acoustic study of St Austell Bay carried out by a survey boat pinpointed 359 hectares (887 acres) of seagrass hugging the coastline, and divers sent in to examine the site close up recorded 56 species living in the rich habitat.
Cornwall Wildlife Trust described it as a hugely positive find but said work was needed to protect the bed and further surveys should be carried out to find out if there were other beds in nearby areas.
Abby Crosby, marine conservation officer for the trust, said: “The discovery of extensive surviving seagrass beds in St Austell Bay is a very exciting development. Seagrass is one of the largest carbon sinks we have globally, despite covering only 0.1% of the ocean floor.
“It also serves as a shelter, feeding ground and nursery for a host of marine life, including vulnerable species such as seahorses, and the young of commercial fish and seafood stocks. Seagrass beds play an important role in helping to combat erosion of the coastline from the waves, as storms increase in their intensity due to climate change.”
Seagrass meadows, which can flower and photosynthesise in shallow seas, are important because they stabilise the sediments in which they grow and provide food and shelter for other species thereby enhancing biodiversity.
They also sequester and store carbon in their leaves, branches and root systems, as well as in the sediment below and around them. When seagrass meadows are stable and healthy, they can be highly effective carbon sinks.
Among the marine animals seen by divers in the seagrass were the short-snouted seahorse, broadnosed pipefish, little cuttlefish and scallops.
The volunteer divers also examined beds of maerl, delicate coral-like algae, a little further out from the coast, where they found an additional 66 species including the curled octopus and streaked gurnard.
Some areas within the beds were free of litter and other human impact, though rubbish – and a large number of golf balls hit errantly from a seaside course – and some old fishing gear were found in other places.
The St Austell Bay blue carbon mapping project is part of the G7 legacy project for nature recovery announced at the world leaders’ summit held in Cornwall in 2021.
A report on the project, published by Cornwall Wildlife Trust and Natural England, said that some poor weather and limited financial resources meant that not all the planned surveying work had been completed. It says management measures to protect the seagrass and maerl such as making them more visible to sea users through marker buoys should be considered.
Seagrass beds are thought to have surrounded much of the UK before the Industrial Revolution but the wildlife trust said about 92% was lost in the last century. The decline has been caused by pollution, disease and coastal development. Additionally, damage from anchoring, moorings and dredging has affected the seagrass beds.
Crosby said the project was a “significant first step” in understanding the extent and quality of blue carbon habitats in the St Austell Bay area.
She added: “We look forward to collaborating with a wide range of people, from local residents to marine business and government organisations, to ensure we protect these special marine habitats which will benefit all marine life and our coastal communities into the future.”
