Underwater power cables mesmerise brown crabs and cause biological changes which could lead to greater infection risk, scientists have discovered.

The cables for offshore renewable energy emit an electromagnetic field which attracts the crabs and causes them to sit still.

A study of around 60 brown crabs at the St Abbs Marine Station in the Scottish Borders found higher levels of electromagnetism caused cellular changes in the crabs, affecting blood cells.

Alastair Lyndon, from Heriot-Watt University, said: “Underwater cables emit an electromagnetic field.

“When it’s at a strength of 500 microTeslas and above, which is about 5% of the strength of a fridge door magnet, the crabs seem to be attracted to it and just sit still.

“That’s not a problem in itself. But if they’re not moving they’re not foraging for food or seeking a mate.

“The change in activity levels also leads to changes in sugar metabolism – they store more sugar and produce less lactate, just like humans.”

The researchers used the marine station’s purpose-built aquarium laboratory for the experiment.

Kevin Scott at St Abbs Marine Station said: “The aquarium lab is composed entirely of non-metallic materials, which means there is minimal electromagnetic interference.

“We found that exposure to higher levels of electromagnetic field strength changed the number of blood cells in the crabs’ bodies.

“This could have a range of consequences, like making them more susceptible to bacterial infection.”

The team warns changes in the species’ behaviour could hit fishing markets, as the crabs are the UK’s second most valuable crustacean catch and the most valuable inshore catch.

A number of offshore wind farms are installed and planned around Scotland’s coast, which require extensive underwater cabling, and researchers said further work is needed to ensure they do not destabilise Scotland’s brown crab population.

Mr Lyndon said: “Male brown crabs migrate up the east coast of Scotland If miles of underwater cabling prove too difficult to resist, they’ll stay put.

“This could mean we have a build-up of male crabs in the south of Scotland, and a paucity of them in the north east and islands, where they are incredibly important for fishermen’s livelihoods and local economies.”

He said one solution would be to bury the cables in the seafloor, but warned it can be expensive, means maintenance is more challenging and cannot be done in some locations.

Mr Lyndon added: “We need to investigate further technical solutions so that we don’t create negative environmental effects while trying to decarbonise our energy supply.”

The study was published in the Journal of Marine Science and Engineering.