Cornwall's largest bed of seagrass off St Austell among biggest in UK

Acoustic surveys have found that St Austell Bay supports 359.1 hectares (887 acres) of subtidal seagrass.

Seagrass is particularly important because, in addition to maintaining the seabed, it is able to store huge amounts of carbon – 35 times faster than the rainforest – preventing it from becoming a greenhouse gas. It is also the only flowering plant able to live in seawater and pollinate while submerged.

The findings come from the St Austell Bay Blue Carbon Mapping Project - part of the G7 Legacy Project for Nature Recovery, announced by the Prime Minister at the G7 Summit held in Cornwall in 2021.

It follows substantial seagrass beds being discovered in Mount’s Bay, and the Fal and Helford estuaries.

The report published today by Cornwall Wildlife Trust and Natural England contains results of a survey carried out in partnership with the Cornwall Inshore Fisheries and Conservation Authority (IFCA).

Boats used echosounder techniques to identify ‘blue carbon’ habitats – areas of the sea that act as highly effective carbon stores. The surveys focused on historically under-recorded habitats of seagrass, which can flower and photosynthesise just like meadows in shallow seas, and beds of the delicate and brittle pink, coral-like algae known as maerl.

Seagrass offers an important habitat for sealife such as plaice (Image: Sean Dixon / Cornwall Wildlife Trust)

In addition to the acoustic mapping, volunteer dive surveyors from Cornwall Wildlife Trust’s Seasearch programme monitored the sites over the course of 22 dives during the project.

The team found an incredible total of 122 different species of plants and animals within the seagrass and maerl beds, proving these sites to have real biodiversity importance.

They even discovered the rare short snouted seahorse in St Austell Bay, and multiple economically valuable scallops.

READ NEXT: Dual-fuel chemical tanker arrives from Vietnam carrying vegetable oil

Cornwall Wildlife Trust marine conservation officer Abby Crosby said: “To better understand the health of our coastal habitats and their potential for both marine recovery and blue carbon storage, it is essential to find out what is there first.

“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.”

A 2021 report in the Frontiers in Science journal estimates that historical UK seagrass meadows – from pre-industrial times when marine life was much richer – could have stored 11.5 megatonnes of carbon and supported around 400 million fish.