New Seaweed Species Discovered During Underwater Surveys Off Cornwall

Main photo credit: The extensive healthy maerl bed in the Fal Estuary, taken by Natural England divers on the day of filming. Credit Angela Gall – Natural England

Natural England divers have helped solve a 40-year scientific mystery after discovering a seaweed species previously unknown to science during surveys of ancient marine habitats off Cornwall.

A tiny red seaweed measuring just a few millimetres across has been identified as a new species following underwater surveys carried out by Natural England’s marine dive team off the south coast of Cornwall.

The discovery was made among Cornwall’s ancient maerl beds – underwater habitats formed from free-living, calcified red seaweeds known as rhodoliths. These small, pink, branching structures accumulate slowly on the seabed, creating complex habitats that support a huge variety of marine life.

The significance of the discovery was highlighted when the BBC joined Natural England’s dive team to film its work surveying the seabed and investigating the newly identified species.

A mystery decades in the making

The newly identified seaweed belongs to the Ceramium group, sometimes known as pincer weed. Its tiny size meant that it had remained unidentified for decades.

Seaweed expert Professor Christine Maggs first encountered the unusual Ceramium in the early 1980s and had been trying to establish exactly what it was ever since.

To confirm its identity, Natural England divers collected living fragments which were subsequently grown in laboratory conditions and examined using DNA sequencing. This confirmed that the seaweed was a species new to science.

During the BBC filming, another specimen was found carrying tetrasporangia, specialised reproductive structures found in some seaweeds, particularly red algae. These structures had not previously been recorded on the newly identified species.

More rare discoveries

The surveys have revealed that the tiny new species isn’t the only interesting discovery hiding within Cornwall’s maerl beds.

The team recorded Ulva rigida, a species of green sea lettuce that had never previously been confirmed in UK waters.

They also found Neofolia rosea, known as little rosy tongue weed, which had only previously been recorded once in Britain, also in the Fal Estuary.

Another significant find was Bonnemaisonia clavata, a delicate red seaweed that had not been recorded in British waters since the 18th century.

More than 380 species have already been recorded living on the surface of the maerl beds, with many more thought to live within the maerl itself or appear at different times of the year.

Ancient habitats beneath Cornwall’s waters

Maerl beds are among the most biodiverse shallow-water habitats found in the north-east Atlantic.

The rhodoliths grow at an extremely slow rate of around half a millimetre each year, meaning some of the maerl beds found in the Fal Estuary are estimated to be up to 4,000 years old.

These ancient habitats provide important nursery grounds for young fish and shellfish, while also offering shelter to a wide variety of marine species. They also play a role in storing carbon within the seabed sediments.

Most of England’s maerl is concentrated along the south coast of Cornwall. Since 2023, Natural England surveys have identified extensive areas of previously unknown maerl within and around the Falmouth Bay to St Austell Bay Special Protection Area.

The discoveries demonstrate that even relatively well-studied coastal waters can still contain marine life that has yet to be fully understood.

However, maerl habitats are vulnerable to physical disturbance, pollution and the effects of climate change.

Working to protect Cornwall’s maerl

Natural England has been working with partners to map, understand and protect Cornwall’s maerl beds.

Over the past two years, detailed dive surveys and seabed mapping have been carried out across the Falmouth Bay to St Austell Bay Special Protection Area and the Fal and Helford Special Area of Conservation.

A Cornwall Maerl Conservation Action Plan 2025–2030 has also been developed through the UK’s first dedicated Maerl Forum. The plan brings together scientists, conservationists, marine managers and policymakers and focuses on areas including monitoring, water quality, sustainable fishing, habitat restoration research and public engagement.

Research by the University of Exeter has also examined the genetics of maerl populations across south-west Britain. The work identified a genetically distinct population found only in St Mawes.

The research will help inform future marine management and conservation work, including efforts connected with the global 30by30 commitment to protect and effectively manage 30% of land and sea by 2030.

For Natural England’s dive team, the discovery highlights just how much remains to be found beneath Cornwall’s waters. A tiny piece of seaweed that had puzzled scientists for decades has now been identified, while the ancient maerl habitats surrounding it continue to reveal new insights into the richness of Britain’s marine environment.

To find out more about  maerl visit the Cornwall Maerl website

Check out the BBC News story on YouTube. https://youtu.be/OTrg3jPs5vg?si=i0dHehv8HbJCJyBo