Evidence Gap FF.07: Electromagnetic fields (EMF)
Review of current knowledge
Sources of MRE related EMFs include inter array cables between devices (fixed foundations and floating) and substations, and export cables. AC power transmission cables are more commonly used for offshore renewable projects, however, DC cables are also currently used and are expected to become more widely used as the siting of projects moves further offshore (Hutchinson et al 2020b).
Magnetic or electric senses have been reported for a wide range of marine animals, including many groups of fish and several invertebrate groups. The ability to detect electric fields is well documented for elasmobranch species. These are generally considered to be the most electro sensitive species group as they possess a highly sensitive electrosensory system (ampullae of Lorenzini). In addition, species such as lampreys, sturgeons and a few teleost fish also have advanced electro-sensory systems. Few invertebrates have been tested for an electric sense, however, there is evidence of a response to EMFs from various species, including crustaceans such as crabs, shrimp and lobsters (Normandeau et al 2011).
Given the expansion of the MRE industry across Europe and internationally, interest has grown in recent years in improving our understanding of the potential impact of EMF on marine organisms.
In the UK, early studies on the effect of EMFs associated with MRE projects were undertaken by COWRIE (Collaborative Offshore Wind Research into the Environment), an independent body set up by The Crown Estate, and were focused on fish species, particularly elasmobranchs (Gill et al 2005; 2009).
Elasmobranchs naturally detect bioelectric emissions from prey, conspecifics and potential predators and competitors (Gill et al 2005). In addition, they are known to detect magnetic fields (Normandeau et al 2011).
Gill et al (2009) studied whether elasmobranchs responded to controlled EMF with the characteristics and magnitude of EMF associated with offshore wind farm power cables. The study took an experimental research approach where sections of subsea cables were enclosed (mesocosm study) to allow assessment of the responses of elasmobranchs in a semi-natural setting. The research found that the benthic elasmobranchs studied (thornback ray and lesser spotted catshark) can respond to the presence of EMF of the type and intensity associated with subsea cables. However, their response was found not to be predictable and appeared to be species and individual specific. Thornback rays were found to be more likely to move around within the EMF zone whilst some catsharks were found nearer to the cable and restricted their movement within the EMF area. From this study, however, there was no evidence to suggest any positive or negative effect on elasmobranchs as a result of encountering the EMF.
Further research on lesser spotted catsharks (i.e. Kimber et al (2011)) found that this species are able to distinguish some types of electric fields but are either unable to distinguish between or at least show no preference for other types. They showed a significant preference for the stronger DC electric field and a less pronounced, but still significant, preference for an AC electric field. No preference was demonstrated between an artificial and natural DC electric field. These findings suggest that these predators could potentially confuse prey bioelectric fields with artificial electric fields during foraging.
In recent years, there has been an increasing focus and research effort, in improving our knowledge of the impact of EMF on invertebrates, particularly species of commercial importance, and on early life stages.
Some examples of recent and planned future research on EMFs, including existing research on invertebrates and early life stages, are provided below:
- Love et al (2016) studied the effect on marine organisms of EMFs from subsea cables based on in situ observation around energised and unenergised cables in the Pacific Region. This study found no evidence that there were significant differences in fish communities or in invertebrate assemblages between energised and unenergised cables. Similarly, it found no evidence to suggest that electro-sensitive species such as elasmobranchs, were either attracted or repelled by the EMFs emitted from the energised power cables. The study also found that EMFs produced by the energised cables were similar over the three years of the study and along the cables and that the strength of the EMF dissipated quickly with distance from the cables (i.e. approached background levels at about one metre).
- Love et al (2017) studied the potential for energised cables off southern California to impact the Dungeness crab (Metacarcinus magister and other commercially important crab species in the area (Cancer productus). The research found no evidence that the EMF emitted by energised submarine power cables influenced the catchability of these two species. In addition, it found no difference in the responses of crabs to lightly buried versus unburied cables.
- Scott et al (2018) investigated the effect of simulated EMFs emitted from sub-sea power cables on edible crabs in the laboratory and identified a clear attraction to shelters that had a relatively high B-field and a decrease in roaming behaviour. In addition, the daily behavioural and physiological rhythmic processes of the haemolymph L-Lactate and D-Glucose levels were disrupted. The EMF did not however appear to affect stress related parameters (i.e. hemocyanin concentrations, respiration rate, activity level or the antennular flicking rate).
- Hutchison et al (2018; 2020a) quantified biologically relevant behavioural responses of American lobster (Homarus americanus) and the Little skate (Leucoraja erinacea), to EMFs from a subsea high voltage direct current (HVDC) transmission cable. The study found an increase in exploratory/foraging behaviour in skates in response to EMF and a more subtle exploratory response in lobsters. In addition, through direct measurements of the magnetic field and electric field components of the EMF emitted by the cable, it was found that there were DC and, unexpectedly, AC components.
- Cresci et al (2019) studied the orientation mechanisms in haddock larvae through observations of 59 and 102 haddock larvae swimming in the Norwegian Sea and in a magnetic laboratory, respectively. The findings of the research in both settings identified that haddock larvae orientation at sea is guided by a magnetic compass mechanism. A similar study by Cresci et al (2020) focused on herring larvae, found no evidence of magnetic compass orientation for this species, indicating that the orientation direction of herring larvae is not magnetic during this early life stage.
- Taormina et al (2020) studied the potential impact of EMF on the behaviour of recently settled juvenile European lobster and found that juvenile lobsters did not exhibit any change of behaviour when submitted to an artificial magnetic field gradient (maximum intensity of 200 µT) compared to non-exposed lobsters in the ambient magnetic field. In addition, no influence was noted on either the lobsters' ability to find shelter or modified their exploratory behaviour after one week of exposure to anthropogenic magnetic fields (225 ± 5 µT) which remained similar to those observed in control individuals.
- Scott et al (2021) investigated the effects of different strength Electromagnetic Field (EMF) exposure (250 µT, 500 µT, 1000 µT) on the commercially important decapod, edible crab (Cancer pagurus). Stress related parameters were measured (L-Lactate, D-Glucose, Total Haemocyte Count (THC)) in addition to behavioural and response parameters (shelter preference and time spent resting/roaming) over 24 h periods. Exposure to 250 µT was found to have limited impacts, however exposure to 500 and 1000 µT was found to disrupt the L-Lactate and D-Glucose circadian rhythm and alter THC. The findings were that crabs showed clear attraction to EMF exposed shelters with significant reduction in time spent roaming. The study recommended the need for in-situ measurements of EMF from existing cables and suggested that a working limit of a maximum of 250 µT could result in minimal physiological and behavioural changes within this species and should be considered during MRED design and implementation.
- Research is planned to be undertaken in 2021 at St Abbs Marine Station in Scotland, on the effects of EMF from renewable subsea power cables on coastal invertebrates (MASTS 2020). The objective of the research is to investigate the adaptation and resilience of coastal species by testing whether the simulated EMFs from MRE subsea power cables affect the post-disturbance recovery times, as an indicator of stress of coastal invertebrates. Experiments will be undertaken in tanks where various species of invertebrates (including various species of echinoderms, crustaceans and molluscs) will be exposed for 24 hours to either a control set-up or an active Helmholtz-coil used to general EMFs that will simulate those expected around a cable landing site. Individual animals will then be placed in tanks and their behaviour will be recorded using a CCTV system.
In addition to the specific studies outlined above, a number of comprehensive reviews on various key EMF related topics have been recently published covering magnetoreception and electroreception in fish (Formicki et al 2019, Newton et al 2019, respectively) and environmental impacts and interactions with marine organisms (Taormima et al 2018, Hutchison et al 2020b). In addition, the updated State of the Science report published in 2020, includes detailed consideration of the potential risk to fish and invertebrates from EMF associated with MRE projects (Gill and Desender 2020). The State of the Science report identified the following key aspects in relation to future research needs on the impact of EMF on these receptors:
- Cable characteristics and power transmitted determine the sources and intensity of the EMFs emitted. Therefore, quantifying these parameters in the aquatic environment would aid characterising emissions and accurate modelling.
- Field measurements of EMF intensity and its variability within the environment. This requires the development of affordable methods and equipment for measuring EMFs so that measurements taken at MRE project sites can be compared to power outputs of the devices.
- Further research on sensitive life stages (i.e. early embryonic and juvenile phases) of key receptors such as elasmobranchs, crustaceans and molluscs.
- Laboratory studies which consider EMF exposure at different intensities and durations, to determine species-specific thresholds and life stage-specific dose responses.
- Field studies using tagging and tracking systems to gather behavioural, and where appropriate, physiological evidence, for determining potential effects on mobile receptors of encountering multiple cables.
- The undertaking of field studies to address data gaps on the interaction of pelagic species and dynamic cables (cables in the water column).
- Long terms in situ studies to assess the effects of chronic EMF exposures on egg development, hatching success and larval fitness and potential implications of potential attraction of species to hard substrate associated with MRE projects (i.e. reef effect); and
- Demonstration of effects at the relevant biological unit of the species population (i.e. through replicated studies that show evidence of a consistent response).
Next steps in research
From the literature review undertaken it is apparent that our understanding of how marine species interact with EMFs has grown in recent years, however, evidence available to inform assessments and management is still limited and improved knowledge is required in relation to both, pressures and receptors.
The evidence available to date suggests that ecological impacts associated with MRE subsea power cables may be weak or moderate. However, this is based on evidence from a small number of studies and limited data, as a result uncertainty remains in relation to how EMF may affect fish and invertebrates (Gill and Desender 2020).
Taking account of the findings of the literature review presented above in respect of "Evidence Gap FF.07: Electromagnetic fields", the following next steps in research have been identified to address current knowledge gaps:
- Improvement of knowledge and increased facilitation of data sharing with regard to technical information on cable characteristics, cable transmission and measurements of EMFs from existing cables (both AC and DC), including information on cable burial status/location (i.e. buried, surface laid, dynamic).
- Additional research to establish species specific thresholds and further consideration of potential effects on early life stages (eggs and larvae).
- Development of pilot studies in UK operational MRE projects to identify EMF related impacts on fish species and other key receptors, including consideration of species of importance to the fishing industry. Such research could be combined with wider research initiatives to investigate other MRE operational related effects (i.e. reef effects).
- For mobile species, consideration should be given to studies which allow the collection of evidence on repeated exposure due to the encounter of multiple cables. This would facilitate the development of evidence in respect of cumulative impacts which is currently lacking.
- Strategic research to investigate the scale of the effect of EMF exposure on fish and invertebrates that may result in population level impact or economic impact to fisheries.
- Investigation on potential mitigation measures which may reduce potential effects on fish and invertebrates.
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