An egg case study: Chronic exposure to AC electromagnetic fields results in hyperactivity in thornback ray (Raja clavata L.) embryos

Subsea power cables, required for offshore generated wind power transport, emit electromagnetic fields (EMFs) into the marine environment. EMFs also occur naturally, resulting from biotic (animals) and abiotic (geomagnetic field) sources. Skate and oviparous shark embryos in the egg can sense EMF from predators and respond by reducing their normal movement ('freezing response') to prevent detection and subsequent predation. When nursery areas overlap with power cables, embryos will be exposed to varying levels of anthropogenic EMFs and effects thereof on embryonic development is currently understudied. Here, we present behavioral responses of thornback ray (Raja clavata) embryos to varying field-related EMF levels (1.8-4.6 μT) generated by alternating current throughout embryogenesis (∼20 weeks). Chronically exposed individuals were overall more active, including 33 % more tail undulations and 150 % increased body movements, compared to non-exposed individuals. This increased activity suggests that eggs exposed to EMFs generated by subsea power cables might be at risk of increased predation. We found no indications of reduced health or survival after hatching, or changes in development time or biometry. Effects on subsequent life stages cannot be excluded, follow-up studies should observe hatchling development. We did not observe an increase in freezing response resulting from EMF change as described by other researchers who used different types and intensities of EMF cues. We recommend that different species, along with DC exposure, should be studied to gain a more complete insight into the potential effects of EMF exposure during embryogenesis of these EMF-sensitive species.