Female crab (Carcinus maenas) on Submarine Power Cable. Credit: Elizabeth James
- The attraction to electromagnetic fields (EMF) from underwater power cables could potentially disrupt female crab migration patterns and population levels
- Female crabs were affected by magnetic field strengths from subsea power cables found in real ocean environments, not just artificially high levels in labs
- While underwater cables will cover less than 0.1 per cent of the ocean floor by 2050, they could still cause problems for marine life if they're placed in the wrong spots
New research has found that female crabs show significantly greater sensitivity to electromagnetic fields (EMFs) from underwater power cables than males, which transmit electricity from offshore installations including wind farms.
This matters because millions of crabs migrate along coastlines each year to reproduce, and disrupting these patterns could affect marine food chains.
The study, conducted by PhD student Elizabeth James from the University of Portsmouth's Institute of Marine Sciences , exposed 120 juvenile common shore crabs (Carcinus maenas) to electromagnetic fields found near underwater power cables. The results showed significant behavioural differences between male and female responses.
Female crabs were on average almost twice as likely to stay near areas with electromagnetic fields compared to those without them (between 87 and 131 per cent more time). Interestingly, male crabs were not as affected by the electromagnetic fields, showing no consistent spatial preference across different strengths.
Ms James said: "This is the first study to demonstrate sex-specific responses to submarine power cable electromagnetic fields in crabs. The fact that we're seeing such clear behavioural differences between males and females, even at relatively low, as well as high electromagnetic field strengths, suggests that we need to think much more carefully about how offshore energy infrastructure might be affecting marine ecosystems differently than we previously thought."
The research team used a controlled laboratory setup with Helmholtz coils - specialised equipment that creates controlled magnetic fields - to generate precise electromagnetic fields ranging up to 3200 μT (levels which can be emitted by submarine power cables). Over 10-minute trials, researchers tracked crab behaviour including distances moved, zone preferences, and mobility levels using advanced video tracking software.
The amount female crabs moved was also reduced by more than a third (38 per cent) at moderate field strengths (1000 μT). There were even noticeable effects at low EMF levels below 250 μT.
Infographic highlighting the sex-specific electromagnetic fields impact on crabs during the study. James et al 2025
The findings, published in Environmental Science & Technology Letters , suggests that as offshore wind farms expand globally the sex-specific impacts on crustacea could have significant ecological consequences.
If female crabs are drawn to stay near underwater cables instead of continuing their natural migrations, this could affect where they lay their eggs and ultimately impact crab populations along entire coastlines.
While underwater cables will cover less than 0.1 per cent of the ocean floor by 2050, they could still cause major problems if they're placed in the wrong spots - like along routes where crabs migrate to breed. The researchers say scientists need to study how these cables affect male and female sea creatures separately, not just assume they respond the same way.
Co-author, Professor Alex Ford from the University of Portsmouth's School of the Environment and Life Sciences , added: "The sex of an animal often gets overlooked when we look into the impact of pollution to aquatic life. With chemical pollutants sometimes the males are more sensitive because females are able to excrete their contaminants with the 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.
"This research builds on our international efforts to incorporate the effects on behaviour from many types of pollution, when assessing human impacts on our ecosystems. 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."
This University of Portsmouth has an established track record of investigating human impacts on marine life. Previous studies have examined how plastic chemicals affect marine reproduction , monitored how pollution affects the behaviour of marine life , and assessed the presence of "forever chemicals" (PFAS) in coastal waters . Professor Ford's collaboration with the Marine Conservation Society on PFAS contamination recently informed a UK Parliamentary inquiry , demonstrating the University's commitment to research that influences environmental policy.
