Natural England’s underwater surveys of maerl beds off the south coast of Cornwall have uncovered a remarkable array of rare and scientifically important seaweeds, including species never before recorded in the UK.
Among the findings are species last seen centuries ago and a tiny red seaweed now confirmed as completely new to science.
The newly identified Ceramium (pincer weed) found is only a few millimetres across, so small that it has never previously been possible to identify. Divers brought up living fragments to the surface, allowing scientists to grown it in the lab and sequence its DNA for the first time.
These discoveries serve as a reminder of the extraordinary biodiversity surrounding our coastline and the many mysteries it still holds, and also the uniqueness of some of Cornwall’s and seascapes. The vast majority of England’s maerl beds are in Cornwall.
Natural England Senior Marine Officer Angie Gall said:
These discoveries show just how special these habitats are. We’ve already recorded more than 350 species living on the surface of the maerl beds, and that’s only the beginning.
Many more species live hidden within the maerl or appear at different times of year. There is still so much to uncover. Maerl beds are living archives of our natural history. Protecting them is essential if we are to safeguard marine biodiversity for future generations.
World-leading seaweed taxonomy authority Professor Christine Maggs said:
I first encountered this tiny Ceramium in the early 1980s, and I have been wondering about it ever since.
It’s so minute that you can only study it if divers bring it up alive, and even then it takes careful cultivation to get enough material to work with. Natural England’s surveys finally provided the missing piece of a scientific puzzle I’ve been trying to solve for most of my career.
The surveys also recorded Ulva rigida, a green sea lettuce never previously confirmed in the UK, Neofolia rosea (little rosy tongue weed) only found once before in the UK, at this site, and Bonnemaisonia clavata, a delicate red seaweed last seen in British waters in the 18th century.
Maerl beds, formed by slow‑growing, coral‑like red seaweed, are among the most biodiverse shallow‑water habitats in the north‑east Atlantic. These fragile and irreplaceable habitats play a vital role in supporting healthy fisheries, providing nursery grounds and shelter for a wide range of marine life. Maerl beds also play an important role in locking away carbon which becomes trapped in the sediments.
Following initial reports from citizen scientist divers on the Seasearch project, Natural England’s work in 2023 and 2024 led to the discovery of extensive areas of previously unknown maerl beds off England’s south coast, a reminder that even in well-studied waters, significant ecosystems remain hidden.
Seaweed expert Francis Bunker, who discovered the minute Ceramium in these surveys, said:
Finding species new to science in our waters is thrilling. But it also shows how much how much biodiversity is still hidden in these beds and what we stand to lose if these habitats are damaged before we’ve fully understood them.
The findings have striking parallels with other highly biodiverse habitats around the world that are being degraded or destroyed faster than science can describe them. Physical disturbance, for example through scallop dredging, pollution and climate change, poses ongoing threats to maerl beds.
The discoveries reinforce the urgent need to protect these habitats, not only for the remarkable species they support today, but for those yet to be discovered.
