Nearly a decade after Scotland banned bottom trawling across most of the South Arran Marine Protected Area, scientists have uncovered something remarkable beneath the waves. A new University of Exeter study reveals seabed life has tripled, with twice as many species thriving in protected mud compared to fished zones nearby. What was once dismissed as a barren underwater desert is bursting with hidden life.
Decade of Protection Sparks a Stunning Marine Comeback
Researchers from the University of Exeter compared 14 sites in and around the South Arran MPA, off the west coast of Scotland. The findings are striking.
The team recorded more than 1,500 species across their sampling. Protected zones held roughly twice as many seabed species and three times as many individual animals living inside the mud, compared with unprotected areas just outside the boundary.
The strongest recovery showed up where protection was strongest, suggesting half measures simply do not work.
Lead author Dr Ben Harris described what looked like empty mud as anything but. Speaking to Mongabay, he said the seafloor was “really, really dynamic,” even if its small creatures were not the most photogenic on the planet.
Inside the Hidden Mudtropolis Beneath Scottish Waters
Lift a small bucket of Scottish seabed mud and you might be holding an underwater city. In just 100 litres of sediment, the research team counted more than 1,500 organisms across over 150 species.
Among the standout residents were:
- Spoon worms that vacuum food through long flexible probes
- Bobbit worms, the armoured ambush predators with scissor like jaws
- Tower snails, building shells that shape the seabed structure
- Bamboo worms and sea pens, signatures of healthier protected zones
- Brittlestars, fragile cousins of the starfish
Harris called these creatures “important gardeners of the seabed.” They burrow, mix and aerate the mud constantly, doing the same job as earthworms on land.
To grasp the scale, he offered a jaw-dropping comparison. Around eight Mount Everests’ worth of sediment is turned over every minute of every day on the global continental shelf by these tiny animals.
Europe’s Seabeds Suffer Centuries of Damage
The story behind the recovery is also a warning. Europe’s seabeds are the most trawled in the world.
Heavy fishing gear has been dragged across the seafloor since at least the mid 14th century. The European Environment Agency reported that around 86% of the assessed seabed in the Greater North Sea and Celtic Sea showed evidence of physical disturbance from bottom-touching fishing gear.
The damage runs so deep that researchers had no living reference point. To picture what a thriving seabed once looked like, they had to dig into historical records that are 150 to 200 years old.
Old accounts describe what Harris called “animal forests,” dense communities of native oysters, honeycomb worms and other shell-building species covering muddy floors. Almost none of that survives in European waters today.
| Indicator | Inside Protected Zones | Outside MPA |
|---|---|---|
| Individual seabed animals | Up to 3 times more | Baseline |
| Number of species | Around 2 times more | Baseline |
| Epifauna diversity | Bamboo worms, sea pens present | Largely absent |
| Carbon stability | Early signs of stabilising | Disturbed by trawls |
Why Carbon Storage Hangs in the Balance
The Arran study is not only about wildlife. It carries serious climate stakes too.
Seabed sediments lock away huge volumes of organic carbon. When trawl gear scrapes the bottom, that stored carbon can be released back into the ocean and atmosphere.
Researchers found early signs that protection is stabilising the link between mud and carbon. But the climate payoff will take far longer than the biodiversity bounce.
Different species rebuild the system at different stages, the team noted. Carbon storage gains may take decades, closer to the slow recovery of an old growth forest than a quick ecological fix.
Professor Callum Roberts of the University of Exeter put the verdict plainly. “The evidence is clear: protection works. What’s missing now is the urgency to act on it.”
What This Means for Global Ocean Protection
The wider numbers are sobering. Just 0.2% of Europe’s seabed is currently shielded from destructive bottom-towed fishing. About 13.7% of EU marine areas are labelled Marine Protected Areas on paper, but real enforcement against trawling is rare.
For coastal communities, the Arran story carries real hope. The Community of Arran Seabed Trust, known as COAST, campaigned for years before Scotland’s first No Take Zone was created in Lamlash Bay in 2008. The wider South Arran MPA followed in 2014, with fisheries management measures coming into force in February 2016.
Earlier studies in the same waters already showed king scallop density rising 8.5 times after protection, alongside major gains for lobsters and juvenile commercial fish.
“The reason these systems haven’t been protected is because everybody thinks they’re not worth protecting. The reason there’s not much there is because they have been historically ripped clean.” Dr Ben Harris, University of Exeter
Researchers under the Convex Seascape Survey, a collaboration between Blue Marine Foundation, the University of Exeter and Convex Group, are now replicating the Arran method in New Zealand and Bermuda. The goal is to find out whether muddy floors elsewhere can bounce back the same way.
The Scottish blueprint is already inspiring calls for stricter protection across the UK, the EU and beyond. With ocean health, fisheries and climate goals all linked to the seabed, scientists argue the world cannot afford to keep treating mud as worthless.
Nearly ten years of leaving the Arran seafloor alone has produced a quiet underwater revival that may reshape global ocean policy. Years of patient campaigning by a small island community have shown that give the ocean a break, and it will come back. The mud creatures of Arran are not glamorous, but they are writing one of the most hopeful environmental stories of the decade, and a reminder that the smallest lives often carry the biggest meaning. Have you seen any marine recovery near your own coast? Share your thoughts in the comments below and tell us if you think more seas should be protected from bottom trawling.
