Sex-dependent behavioural responses of Palaemon varians to submarine power cable electromagnetic fields

The expansion of submarine power cables (SPCs) associated with offshore renewable energy is increasing the prevalence of electromagnetic fields (EMFs) in coastal environments. These fields fall within the sensory detection range of many crustaceans, however behavioural consequences, particularly in smaller decapods, remain poorly investigated. The estuarine shrimp Palaemon varians provides an ecologically relevant model for examining behavioural responses to SPC relevant EMF exposure. Here, we tested whether EMFs alter locomotor, spatial and social behaviour in male and female P. varians under solitary and grouped conditions. Individuals were exposed to EMF gradients with peak intensities of up to 500 μT and behavioural responses were quantified across multiple endpoints including locomotor activity, spatial zone occupancy, aggregation and contact behaviour. Across individual behavioural metrics, EMF exposure did not produce consistent significant differences from controls. To assess integrated behavioural responses, multivariate analyses were conducted, revealing a significant EMF and sex interaction in both solitary and grouped contexts, indicating that behavioural responses to EMF differed between males and females and may be obscured when sexes are analysed together. Principal component analysis showed that behavioural variation in solitary P. varians was structured primarily by spatial positioning and locomotor axes, whereas behavioural variation in grouped P. varians was by social cohesion processes. Sex and social context explained more behavioural variation than EMF exposure alone. In solitary individuals, males exhibiting higher locomotor activity and greater use of distal zones, whereas females showed greater proximity to the EMF proximal COIL region. Under grouped conditions, behavioural variation was dominated by social interactions, and sex differences were reduced. Within each sex, EMF exposure did not produce consistent changes in locomotor or spatial behaviour. A single univariate effect was detected, with males showing increased occupancy of the MID zone at 250 μT, however, this response was not observed at other field strengths and was not supported by changes in other behavioural metrics. Overall, short-term exposure to SPC relevant EMF gradients did not produce consistent behavioural disruption in P. varians. Instead, EMF effects were subtle, sex-dependent and detectable only when behavioural responses were analysed using multivariate approaches, indicating that behavioural variation is driven primarily by biological and social factors rather than EMF exposure alone.