Crab migration is disrupted by offshore wind farm cables

Offshore wind farms promise clean power, but their cables may disturb life underwater. These cables carry electricity across the seabed and give off electromagnetic fields (EMFs). A new study shows that female crabs react strongly to those fields, which could change where they travel and breed.

Crabs might seem small in the grand picture, but their migrations matter. Each year, millions move along coastlines to reproduce. Fish, birds, and even people depend on them. Interrupting those patterns could shake food chains from the bottom up.

Influence of cables on crabs

Elizabeth James, a Ph.D. student at the University of Portsmouth, led the research. She tested 120 juvenile shore crabs in a lab. Helmholtz coils created controlled magnetic fields like those near real subsea cables and video tracking software followed every crab move.

The result: female crabs stuck around. They spent up to 131 percent more time in zones with EMFs than in cable-free zones. Males showed no clear preference. “This is the first study to demonstrate sex-specific responses to submarine power cable electromagnetic fields in crabs,” James said.

“The fact that we’re seeing clear behavioral differences between males and females at relatively low, as well as high electromagnetic field strengths, suggests that we need to think about how offshore energy infrastructure might be affecting marine ecosystems differently than we thought.”

Movement disrupted by low EMFs

The surprise didn’t stop there. Female crabs also slowed down. At moderate field strengths, they moved 38 percent less than normal. Even low levels below 250 μT changed behavior.

Male crabs, in contrast, stayed unpredictable – sometimes moving more, sometimes less – with no pattern.

This matters because the levels tested match what exists near live cables in the sea. It shows that subtle changes can happen in everyday conditions, not just in extreme lab setups.

Invisible barriers for crabs

Migration drives the life cycle of crabs. If female crabs linger by cables instead of moving on, egg-laying could shift to new locations.

That shift may lower survival rates and cut population sizes. Shorebirds, fish, and other predators that rely on crabs would feel the loss too.

By 2050, cables may cover less than 0.1 percent of the seafloor. That sounds small, but placement counts. A badly placed cable on a migration route could act like an invisible barrier.

Female crabs show stronger response

The sex of an animal often gets overlooked when looking into the impact of pollution to aquatic life. Researchers pointed out that when it comes to chemical pollutants, males are sometimes more sensitive because females can excrete contaminants through their eggs or offspring.

“In this instance, the female crabs were more sensitive which might be down to a unique ability to detect electromagnetic fields which we are exploring further,” said study co-author Professor Alex Ford.

“This research builds on our international efforts to incorporate the effects on behavior from many types of pollution, when assessing human impacts on our ecosystems.”

Professor Ford noted that as we rapidly expand offshore renewable energy to meet climate targets, we need to ensure we’re not inadvertently creating new environmental problems while solving others.

Blind spots in ocean science

The University of Portsmouth has a history of testing how human activity shapes ocean life. Past work looked at plastics, pollution-driven behavior changes, and PFAS chemicals.

That research even guided a UK Parliamentary inquiry. The crab study adds another piece: sex-specific effects.

Ignoring these differences risks blind spots. Male and female animals don’t always react in the same way. Energy planning must account for both.

Cables stretch across the seafloor

The timing of these findings matters. Offshore wind is booming worldwide. Europe already hosts thousands of turbines, and Asia is racing to catch up.

Each turbine connects to shore through cables buried under sand or rock. Multiply that across hundreds of projects, and the network stretches for thousands of miles.

If every cable has a small effect on behavior, the sum could be huge. Scientists argue that cable planning should receive as much attention as turbine placement. After all, a turbine above water is obvious. A cable below water is invisible, but still powerful.

It’s not just crabs at risk

Crabs are only the start. Many sea creatures sense magnetic fields. Sea turtles use them to navigate across oceans, and salmon rely on them during river-to-sea migrations.

If cables disrupt crabs, other species may feel the pull as well. Research into those links is just beginning.

The fact that female crabs reacted more strongly than males opens new questions. Could female turtles or fish show similar sensitivities? Could whole populations change direction because of a few cables? The answers could shape conservation policy for decades.

Smarter planning needed offshore

The findings raise a question for engineers and policymakers: How do we build clean energy without disrupting vital species? Careful cable placement, shielding technology, and route planning could help. Collaboration across fields will be essential.

Crabs may be the first species to reveal this risk. Others could follow. The lesson is simple: renewable energy and marine health must advance together, or we risk trading one problem for another.

Image credit: Elizabeth James

The study is published in the journal Environmental Science & Technology Letters.

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