Nearly a decade since Scotland established the South Arran Marine Protected Area and banned bottom trawling across much of it, life on the seafloor has thrived, a new study has found.
Scientists surveying the area found three times more seabed organisms and twice as many species compared to nearby unprotected waters.
“What looks like a boring desert of mud, it’s actually really, really dynamic,” lead author Ben Harris, a marine ecologist at the University of Exeter in the U.K., told Mongabay by phone. “We saw not necessarily the most glamorous things … but once you get a bit nerdy about it and look a bit deeper, you realize that they’re playing a really important role.”
Researchers found more than 150 species in a small sample of the seafloor, including spoon worms (subclass Echiura), bobbit worms (Eunice aphroditois) and shell-building organisms like tower snails (genus Turritella), which Harris called “important gardeners of the seabed … all performing different roles.”
“There’s like eight Mount Everest’s worth of sediments being turned over every minute of every day on the global continental shelf by these small animals,” he added. This movement is important for carbon storage, and in the South Arran MPA, these animals are starting to rebuild a long-lost ecosystem that once thrived at the bottom of the sea.
Europe’s seabeds are the most trawled in the world. Heavy fishing gear has been dragged along the seafloor there since at least the mid-14th century, destroying those ecosystems. Approximately ”86% of the assessed seabed in the Greater North Sea and Celtic Sea” showed “evidence of physical disturbance by bottom-touching fishing gear,” the European Environment Agency previously reported.
In fact, Europe’s seabeds are so extensively destroyed that to find a reference for a healthy seabed ecosystem, researchers turned to historical records. There are no surviving seabeds that meet the old descriptions.
“So much of the continental shelf that is soft sediment has been trawled for so long, that we haven’t really recorded what was there very well before we destroyed it,” Harris said. The records that describe what a healthy European continental shelf looked like are from 150 to 200 years ago.
“Some of these records are incredible, and they describe these animal forests just off the coast of the U.K. that are covered in very biodiverse animal communities,” he said. “There’s all these descriptions of biogenic crust.”
That “crust” could have been a layer of marine animals, species like oysters (Ostrea edulis) or honeycomb worms (Sabellaria alveolata) blanketing the soft, muddy seafloor, and forming a rich substrate sustaining other forms of life, like corals and sponges.
In total, the research team recorded more than 1,500 organisms in approximately 100 liters (26 gallons) of sediment. “Extrapolate that over the entire region of the MPA, and you’re looking at billions of organisms,” Harris added.
Banner image: Seabed in the South Arran Marine Protected Area. Image courtesy of Henley Spiers.
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