Understanding the effects of electromagnetic field emissions from Marine Renewable Energy Devices (MREDs) on the commercially important edible crab, Cancer pagurus (L.)

Abstract

The effects of simulated electromagnetic fields (EMF), emitted from sub-sea power cables, on the commercially important decapod, edible crab (Cancer pagurus), were assessed. Stress related parameters were measured (L-Lactate, D-Glucose, Haemocyanin and respiration rate) along with behavioural and response parameters (antennular flicking, activity level, attraction/avoidance, shelter preference and time spent resting/roaming) during 24-hour periods. Exposure to EMF had no effect on Haemocyanin concentrations, respiration rate, activity level or antennular flicking rate. EMF exposure significantly disrupted haemolymph L-Lactate and D-Glucose natural circadian rhythms. Crabs showed a clear attraction to EMF exposed shelter (69%) compared to control shelter (9%) and significantly reduced their time spent roaming by 21%. Consequently, EMF emitted from Marine Renewable Energy Devices (MREDs) will likely affect edible crabs both behaviourally and physiologically, suggesting that the impact of EMF on crustaceans must be considered when planning MREDs.

Full text

Understanding the effects of electromagnetic field emissions from Marine Renewable Energy
Devices (MREDs) on the commercially important edible crab, Cancer pagurus (L.)
Kevin Scott a, b, Petra Harsanyi a, Alastair R. Lyndon b.
a St Abbs Marine Station, The Harbour, St Abbs, Scotland, UK, TD14 5PW
b Centre for Marine Biodiversity & Biotechnology, John Muir Building, Heriot Watt University,
Edinburgh, Scotland, UK, EH14 4AS.
Corresponding author: Kevin Scott
Email: kevin.scott@marinestation.co.uk
Tel: +(44) 1890771688
Email addresses:
Kevin Scott: kevin.scott@marinestation.co.uk
Petra Harsanyi: petra.harsanyi@marinestation.co.uk
Alastair Lyndon: A.R.Lyndon@hw.ac.uk
Key Words: Cancer pagurus; edible crab; electromagnetic field; environmental stressor; marine
renewable energy.
Conflicts of interest: none.
Contributions: All research was designed and conducted by Kevin Scott and Petra Harsanyi with
regular input from Alastair Lyndon. All three authors contributed to the article preparation.
Funding: All work was carried out at St Abbs Marine Station and Heriot Watt University with funding
obtained from the Nesbitt-Cleland Trust. Consumables were funded through St Abbs Marine Station.

Abstract
The effects of simulated electromagnetic fields (EMF), emitted from sub-sea power cables, on the
commercially important decapod, edible crab (Cancer pagurus), were assessed. Stress related
parameters were measured (L-Lactate, D-Glucose, Haemocyanin and respiration rate) along with
behavioural and response parameters (antennular flicking, activity level, attraction/avoidance, shelter
preference and time spent resting/roaming) during 24-hour periods. Exposure to EMF had no effect
on Haemocyanin concentrations, respiration rate, activity level or antennular flicking rate. EMF
exposure significantly disrupted haemolymph L-Lactate and D-Glucose natural circadian rhythms.
Crabs showed a clear attraction to EMF exposed shelter (69%) compared to control shelter (9%) and
significantly reduced their time spent roaming by 21%. Consequently, EMF emitted from Marine
Renewable Energy Devices (MREDs) will likely affect edible crabs both behaviourally and
physiologically, suggesting that the impact of EMF on crustaceans must be considered when planning
MREDs.

1. Introduction
The predicted decline in non-renewable
energy sources in future decades (Pimentel et
al. 2002) indicates the need for alternative
renewable energy sources. Due to reduced
planning constraints, lack of inexpensive land
near major population centres (Bilgili et al.
2011), and perceived aesthetic problems with
many renewable energy structures (Gill 2005),
there is increasing pressure to move potential
locations offshore. Wind speeds tend to be
significantly higher offshore than onshore thus
producing larger amounts of energy per
turbine (Bilgili et al. 2011). Vast open spaces
offshore also help avoid wake effects (shading
effect of a turbine on those downwind of it) by
allowing turbines to be placed at greater
distances apart (Chowdhury et al. 2012). As
the global energy demand grows, inshore
areas are increasingly being utilised by the
energy sector looking to increase energy
production via wave and tidal energy devices
(Frid et al. 2012). Therefore, there is a
requirement for appropriate assessment of the
implications of both offshore and inshore
renewable energy generation with regards to
current ecological status and potential future
consequences (Gill 2005). Currently, the UK is
the largest global producer of electricity from
offshore wind farms and has more projects in
planning or construction than any other
country (Smith et al. 1999; Crown Estates
2017). Proposed sites and developments are
based on current knowledge and assessments
of the local environment, despite relatively
little being known about the ecological effects
of such developments on marine benthic
organisms. Some studies suggest that turbine
arrays could increase biodiversity through new
habitat provision (Landers et al. 2001;
Lindeboom et al. 2011), whereas detrimental
effects of turbine arrays on birds (Garthe and
Hüppop, 2004) and fish (Westerberg and
Lagenfelt 2008) have also been found.
Furthermore, it is feared that marine mammals
might be sensitive to minor changes in
magnetic fields associated with these
developments (Walker et al. 2003). There is
currently a gap in our knowledge of the effects
of these arrays on crustaceans.
Electromagnetic fields (EMF) are associated
with Marine Renewable Energy Devices
(MREDs). EMFs originate from both
anthropogenic (telecommunication cables,
power cables, marine renewable energy
devices) and natural (Earth’s natural
geomagnetic field) sources. It has been shown
that industry-standard AC cables can be
effectively insulated to prevent electric field (E-
field) emissions but not magnetic field (B-field)
emissions (Gill 2005). Standard cable
configurations combined with the existing B-
field creates induced electromagnetic fields
(iEM fields) (Gill 2005). The magnetic field (B-
field) leakage has been shown to be of concern
as it will interact with magnetite-based internal
compasses in marine organisms (Öhman et al.
2007). Electric currents between 850 and 1600
Amperes (A) tend to be found in undersea
cables consequently producing an
electromagnetic field of around 3.20 millitesla
(mT) (1,600A) in a perfect wire (Bochert and
Zettler, 2006). As with all electromagnetic
fields this quickly diminishes away from the
source, with values of around 0.32mT and
0.11mT at 1 metre (m) and 4 m respectively
(Bochert and Zettler 2006). In a report by
Normandeau et al. (2011) there was shown to
be a great variation in electromagnetic field
strength arising from different structures,
cables and current values. In a recent report
(Thomsen et al. 2015) higher EMF emission
values were recorded for export cables
compared to inter turbine cables. It was also
noted in this report that EMF values recorded
were considerably higher around the cables
than around the wind turbine bases. An
assessment of the literature (COWRIE 2003)
highlights that the current state of knowledge
on EMF strengths emitted by undersea power
cables is insufficient to allow an informed
assessment. The European edible crab, Cancer
pagurus L., is found throughout Western

Europe from Norway to northern France. They
are commonly found from the shoreline to
offshore depths around 90m. They are a
heavily exploited commercial species with the
present UK and Ireland annual catch around
34,600 tonnes (Bannister 2009). There is a high
probability that this species will encounter sub-
sea power cables resulting in increased EMF
exposures, potentially leading to stress
responses. In crustaceans, haemolymph
analysis enables measurement of stress
through detection of abnormalities in internal
chemical processes. Previous studies (Taylor et
al. 1997; Durand et al. 2000; Bergmann et al.
2001; Lorenzon et al. 2007) show that L-Lactate
and D-Glucose are useful measures of stress in
crustaceans, whilst respiration rates in marine
organisms are also reliable indicators of certain
environmental stressors (Paterson and
Spanoghe 1997; Doney et al. 2012; Brown et al.
2013). It is also known that behavioural and
response parameters (attraction/avoidance,
antennular flicking rate, and activity level) can
be affected by stress (Stoner 2012). The aim of
the present paper is to determine the effects
of EMFs on edible crabs using a combination of
the above stress indicators.
2. Methods and Materials
Intermoult crabs were obtained from local
fishermen and the St Abbs and Eyemouth
Voluntary Marine Reserve (St Abbs,
Berwickshire, UK) for each experiment. Crabs
were kept in 1000L flow through tanks with
ambient sea temperature and natural
photoperiod for a minimum acclimation
period of 1 week at densities of no more than
5 crabs per tank. Each crab was sexed,
carapace width measured (mm) and a
condition assigned using a condition index
(Table 1). Crabs were categorized into size
classes based on carapace width (10-79mm –
small, 80-120mm – medium, 121mm+ - large).
2.1. Physiological Analyses
2.1.1. Haemolymph Analysis
During experimentation four 70L tanks were
set up with flow through seawater (UV
sterilised and filtered) which was temperature
controlled (TECO TK1000) to ambient
conditions. Temperature and light intensity
was constantly measured via data loggers
(Onset HOBO temperature/light pendant).
Within each tank a perforated plastic
enclosure enabled the crab to be held in
position over the magnets. The EMF was
produced by placing four electric solenoid
magnets (24V) connected to variable power
supplies (QW-MS305D) on ceramic tiles
underneath the tanks. The magnets were run
at full power, thus creating an electromagnetic
field (peak 40mT measured by an AlphaLab, Inc
Gaussmeter Model GM-2) which covered the
experimental area. The experiment was
repeated using a lower strength EMF (peak
2.8mT) to correspond with the expected,
although highly variable, levels on the surface
of a sub-sea power cable and correspond to
those in previous studies (Bochert and Zettler,
2006).
Haemolymph samples were collected, within
60 seconds, from the arthrodial membrane at
Index
Description
1 – Perfect
2 – Good
3 – Ok
4 – Poor
5 - Bad
Body intact with no damage, black spot or other visible defects.
One or two legs missing no carapace damage.
More than two legs missing, limited carapace damage or slight blackspot.
One or both claws missing, damaged carapace and widespread blackspot.
Legs and claws missing, extensive carapace damage and/or blackspot.
Table 1 Condition index for Cancer pagurus. All crabs used throughout these experiments were grade 1 or 2
(Adapted from Haig et al. 2015)

the base of the fifth walking leg using 1ml
syringes with 25G needles. Samples of 250µl,
300µl and 700µl were collected from the
different size groups respectively.
Haemolymph was transferred into 1.5ml
cryogenic vials, with 50µl of haemolymph from
each sample stored in a separate vial for
Haemocyanin analysis. Samples were frozen in
liquid Nitrogen and stored in a freezer (-25°C).
To obtain baseline data, haemolymph was
collected before exposure (0h) then again after
4h, 8h and 24h. All haemolymph collection was
staggered with 5 minutes between each
sample to ensure time consistency throughout
the experiment. For all experiments, sample
times were as follows: 0h (09:00), 2h (11:00),
4h (13:00), 6h (15:00), 8h (17:00) and 24h
(09:00).
Haemolymph was deproteinated using the
procedure of Paterson and Spanoghe (1997).
Samples were thawed, vortexed and mixed
with an equal volume of chilled 0.6M
perchloric acid (BDH 10175). Inactivated
proteins were separated by centrifugation at
25,000g for 10 minutes (Eppendorf 5417C,
rotor 30 x 1.5-2ml). After neutralizing the
supernatant with 3M potassium hydroxide
(BDH 29628) the precipitated potassium
perchlorate was separated by centrifuging at
25,000g for a further 10 min. The supernatant
was then frozen and stored at -25°C.
2.1.1.1. D-Glucose
D-Glucose concentration was measured using a
D-Glucose assay kit (Sigma GAGO20-1KT)
according to the procedure in Barrento et al.
(2010). Haemolymph samples were incubated
for 30 min at 37°C with an equal part of the
assay reagent. 300µl of 12N sulphuric acid
(BDH) was added to stop the reaction and the
solution added to a 96 well flat-bottomed
microplate (Wheaton 712122). The plates
were then analysed spectrophotometrically at
540nm (Molecular Devices, Spectramax M5)
and D-Glucose concentration calculated using a
calibration curve of standards with a known
concentration.
2.1.1.2. L-Lactate
L-Lactate concentration of deproteinated
haemolymph samples were measured using L-
Lactate reagent (Trinity Biotech, Wicklow,
Ireland no. 735-10), per the procedure
described by Barrento et al. (2010). Samples of
haemolymph (2.8µl) were mixed with L-Lactate
reagent (280µl), then incubated for 10 min at
room temperature. These were then added
into the wells of a 96-well flat-bottom
microplate. The plate was then analysed
spectrophotometrically at 540nm and L-
Lactate concentration was calculated from a
calibration curve using standards of known
concentration (Trinity Biotech, Wicklow,
Ireland L-Lactate standards set no. 735-11).
2.1.1.3. Haemocyanin
Haemocyanin concentrations were
determined spectrophotometrically. 50µl of
haemolymph was diluted with 2ml chilled
distilled water, 280µL was added to the wells
of the 96-well flat-bottom microplate and the
absorbance at 335nm was measured twice.
Haemocyanin concentration (mg/ml) was
calculated from the molar extinction
coefficient E1 cm
mM = 17.26, as previously
described by Harris and Andrews (2005).
2.1.2. Respiration
Thirty juvenile (≤79mm carapace width)
intermoult crabs were collected from the
intertidal zone around St Abbs and placed into
two 1000L tanks with seawater flow-through.
Crabs with a carapace width of over 80mm
were too large for the respiration chamber so
were discarded. Inside a Helmholtz coil (2.8mT)
a 46L flow through tank was set up as a water
bath, with filtered, UV sterilised seawater
connected to a sump tank and temperature
control unit to ensure temperature stability. A
0.3L respiration chamber was filled with UV
sterilised filtered seawater and placed into the
water bath. The fibre optic probe (Presens
polymer optical fibre POF) was attached to the
chamber. An optical oxygen meter (Presens
Fibox 3) was used to measure oxygen levels
using Presens PSt3 (detection limit 15ppb)

sensor spots. This meter was connected to a
computer and a blank was run for a period of
30 minutes. To eliminate bacterial respiration
from water samples, a blank was run prior to
each trial and the information obtained was
considered when calculating oxygen
consumption of the crabs. The system was
calibrated using a conventional two-point
oxygen-free and oxygen-saturated system.
Oxygen-free water was obtained using Sodium
sulphite (Na2SO3) to remove any oxygen, whilst
oxygen saturation was achieved through
bubbling air vigorously into the water sample
for a period of 20 minutes, stirring to ensure
the water was not supersaturated.
Crabs were randomly selected, weighed and
carapace width measured. The crabs were
then placed into the respiration chamber and
acclimated for 1 hour with the water flow-
through valve open. After acclimation, the
valve was closed and measurements taken
until a limit of 60% air saturation was reached,
or for a total of 30 minutes. Fifteen individuals
were ran as control with the Helmholtz coil
switched off and 15 were acclimated with no
EMF present then subjected to an EMF for the
duration of the experiment. The % air
saturation was recorded for each individual
and converted to oxygen consumption
(mg/g/h).
2.1.3. Helmholtz Coil
Two Helmholtz coils were set up with four 12L
glass tanks each, situated in a recirculated
temperature controlled water bath. Tank sides
were covered with netting to reduce visual
stimuli. Tanks were kept at 10°C and were
constantly aerated with air stones. Ten large
male and 10 large female crabs were randomly
selected (carapace width 121mm+), weighed
and carapace width recorded before being
placed into the experimental tanks. After a 1
hour acclimation period, baseline
haemolymph samples were taken from each
crab (800µL) and one of the Helmholtz coils
switched on, with the other acting as a control.
Subsequent haemolymph samples were taken
at 2, 4 and 6 hours. Haemolymph was sampled
using the previously mentioned protocol. After
6 hours, the Helmholtz coil was switched off
and the crabs were left overnight. 24 hours
after the baseline haemolymph sample was
taken another baseline sample was taken and
the other Helmholtz coil was switched on and
further samples taken at the same times as the
previous day. This allowed all crabs to be
sampled during exposure to EMF and control
conditions and helped to eliminate individual
variances by comparing an individual
throughout both treatments. The EMF created
by the Helmholtz coil was measured and
mapped and gave a field strength of 2.8mT
uniformly distributed throughout the
experimental area. Three additional individual
crabs were sampled over the two-day
experiment with no exposure to EMF to
account for any handling stress. No elevated
stress levels were detected. The aims of these
trials were to detect any changes in
haemolymph parameters over a shorter period
of time. Large crabs were utilised to allow
larger volumes of haemolymph to be sampled
over a short time frame.
2.2. Behavioural Analysis
2.2.1. Antennular Flicking Rate
A 12L glass tank was set up with a 40L sump
tank containing UV sterilised filtered sea water
that was temperature controlled (TECO
TK1000) to 12°C. The experimental tank was
placed on top of 4 solenoid electromagnets to
create an EMF of 2.8mT. The inflow and
outflow were separated from the crab inside
the tank by inserting a perforated plastic sheet
to reduce visual disturbance. Experimental
tanks were placed behind screens to avoid
external stimuli. Crabs were acclimated to the
experimental tanks for 30 minutes prior to
testing after which the camera was set to
record via a remote control. The crab was
recorded for 10 minutes under control
conditions, then a further 10 minutes with an
EMF present. After each trial, the tanks were
sterilised and underwent a full water change to
reduce chemical cues which may affect

antennular flicking rates. The system was
monitored for temperature, dissolved oxygen
and salinity during all trials.
The video data was post-processed with
flicking rate counted for both antennules by a
minimum of 3 trained people per video file for
accuracy. Trials where the crab was asleep or
did not exhibit any antennular flicking were
discarded.
2.2.2. Activity Level and Side Selection
Four 70L experimental tanks were set up and
connected to a 1000L temperature-controlled
sump tank which received a constant supply of
UV sterilised filtered sea water. The sides of
the experimental tanks were shaded to reduce
visual disturbances. A wide aperture mesh was
placed over the top of the tanks to prevent the
crabs from escaping. Water was pumped from
the sump tank into the four experimental tanks
at an equal rate for the duration of the
experiment and the temperature was
constantly monitored using data loggers
(Onset HOBO). After each trial the tanks were
drained, sterilised (Virkon aquatic) and refilled.
Four waterproof Infrared cameras were
suspended above the experimental tanks and
set to record during each trial. The trials
consisted of:
1. Day conditions – (7 hours 30 minutes
(08:30am-16:00pm)
2. Night conditions – (8 hours (20:00pm-
04:00am)
The footage from each tank was post
processed then analysed using Solomon Coder
(version – beta 17.03.22). Each video file was
broken down to still images at 1 minute
intervals for the duration of the trial. The
position of the crab in each image was
analysed and a movement index was created
by assigning a value of 0 to a picture where
there was no movement, when compared to
the previous picture, and a value of 1 where
there was movement. The total movement
index score was recorded for each tank
throughout all the trials and used to indicate
activity levels in the crabs. The individual
pictures were analysed to determine the
percentage of time each crab spent on either
side of the tank (magnet or non-magnet). This
was used to indicate an attraction to or
avoidance of the EMF. Trials where there was
no movement for the entire duration or the
crab did not experience both sides of the tank
were omitted. This was deemed necessary as
the individual would not be making a choice
based on treatment preference. It was
concluded during preliminary trials that the
crabs spent a significant amount of time in the
corners of the tanks (approx. 85%), thus
influencing magnet placement.
In the set-up the magnets were evenly spaced
in the middle of one side of the tank in addition
to the two magnets in the corners.
Experiments were conducted under day and
night conditions to fully assess the behaviour
of this crepuscular species. In control
conditions the magnets were present but not
switched on. Magnet placement (left or right)
was randomised to reduce any tank based or
0
10000
20000
30000
40000
Electromagnetic Field Strength
(µT)
Fig. 1. Electromagnetic field strength (µT) over
the tank floor (square inch) represented by the
x axis. Quad magnet set-up with the corner
magnets plus an additional two solenoid
magnets placed just offset to create an EMF
over half of the tank. Magnets were swapped
randomly from the left to right sides of the tank
during replication.

external stimuli that may affect results. The
EMF was mapped for the setup using a 1sq.
inch grid over the base of the tank with each
square being measured by an AlphaLab, Inc
Gaussmeter Model GM-2 (Fig. 1).
2.2.3. Shelter Selection
To further determine the effects of EMFs on
crab behaviour and potential attraction, four
70L experimental tanks were set up with
temperature controlled (13°C), flow through
UV sterilised seawater (Fig. 2.). Six black ABS
plastic shelters (300mm x 200mm x 100mm)
were constructed and secured to the bottom
of the tanks. In two of the tanks two plastic
shelters were set up, with four solenoid
electromagnets placed under each shelter.
During each trial one of the shelters’
electromagnets would be turned on with the
other remaining off as a control. In the two
remaining tanks a single shelter was set up
with four solenoid electromagnets under each,
one tank having the magnets switched on and
the other remaining off as a control.
All magnets were set so that an EMF of 2.8mT
was present under the length of the shelter. An
individual large crab (121+mm carapace width)
was placed in to each tank, using an even split
of male and females. Using the same infrared
camera set-up previously described, the crabs
were recorded from 23:00pm – 06:00am and
the video files post-analysed (Solomon Coder)
to determine the percentage of time spent in
the shelters or free roaming within the tank.
The primary purpose of setting up single
shelter tanks was to determine how the crab
would interact with the shelter under control
conditions, and to determine how the crab
would act if the only shelter available is
subjected to EMF. The dual shelter tanks were
set up to determine if there was an attraction
to EMFs and to discover how crabs would split
their time between seeking shelter and active
roaming.
2.3 Statistics
Results were expressed as mean ± standard
error (SEM). When data met ANOVA
assumptions (per Shapiro-Wilk test for
normality and Levene’s test for equality of
error variances) multiple-comparison tests
(paired t-test, one-way ANOVA, 2-way ANOVA)
were conducted to reveal differences between
groups. If data could not meet ANOVA
assumptions, non-parametrical analysis
(Wilcoxon signed rank test, Mann-Whitney,
Scheirer-Ray-Hare) was performed. Chi-square
test (2 tailed) was utilised for choice
experiments. Post-hoc analysis for parametric
data (Tukey’s test) and non-parametric
(pairwise Mann-Whitney) were conducted. All
statistics were tested at a probability of 0.05
(IBM SPSS Statistics v.23 SPSS Corp. Chicago,
USA).
3. Results
3.1. Physiological Analysis
3.1.1. Haemolymph parameters
Fig. 2. The four different shelter experimental
tanks. Each tank had 4 solenoid electromagnets
underneath each shelter. The shelter with the
electromagnets turned on was randomised
along with the position of each tank to remove
experimental bias and potential external
variable factors. (EMF = magnets on, Control =
magnets off).
EMF shelter only
Control shelter only
EMF and Control choice shelter
Control choice shelter
70L experimental
tank
Black plastic
shelter
Solenoid
electromagnet

Exposure to EMF had a significant effect on the
L-Lactate levels of Cancer pagurus (Table 2).
Throughout the 24-hour high strength (40mT)
exposure L-Lactate levels followed the same
circadian rhythm as the control group, with a
gradual decrease in concentration throughout
the day before a rise at night (Fig. 3). Despite
following the same patterns, the EMF exposed
values were significantly lower at 4h (p<0.05)
and 8h (p<0.05) when compared to 0h. The
control group showed a decrease in
concentration throughout the day, however,
there were no significant differences between
the baseline sample and the remaining
samples taken over the 24 hours. Exposure to
low strength EMF (2.8mT) disrupted the
natural circadian rhythm of L-Lactate causing a
significant decrease throughout the 24-hour
trial. The typical rise and peak values normally
obtained at dawn were absent. The different
EMF strengths had a significant effect on L-
Lactate level (p<0.05). After 4 hours of
exposure crabs exposed to the high strength
EMF had significantly lower concentrations of
L-Lactate compared to those in low strength
EMF.
D-Glucose levels showed a significant increase
between 0h and 4h, 0h and 8h in control crabs
(p<0.05, p<0.05) and in crabs exposed to 40mT
EMF (p<0.01, p<0.05) (Fig.4). Crabs exposed to
2.8mT EMF did not show the significant rise in
D-Glucose level after 8h of exposure.
Haemolymph D-Glucose levels of low and high
strength EMF exposed crabs followed very
similar daily patterns. Although D-Glucose
concentrations after 4h and 8h were lower in
exposed crabs compared to control, the
difference was not statistically significant.
Exposure had no effect on the remaining
haemolymph parameters. Hemocyanin levels
remained constant (44.08±1.01mg/ml)
throughout the trials, with no significant
variation over time or by crab size.
To test whether EMF had any effect on the
measured haemolymph stress parameters
after exposure, half of the crabs used in the
Helmholtz trials were sampled the following
day at 0, 2, 4 and 6 hours. Exposure to EMF has
no lingering effects on the haemolymph stress
parameters. The increase in EMF strength from
2.8mT to 40mT had no effect on the D-Glucose
or Haemocyanin parameters, but showed an
overall decrease in mean L-Lactate
concentration throughout the sample group.
This change in concentration could potentially
be explained by high individual variability or
limits of the assay kit used.
3.1.2. Respiration
The mean respiration rate of juvenile crabs
exposed to EMF was 0.05±0.006mg O2/g/h,
this showed no difference to values obtained
from individuals under control conditions. EMF
exposure did not increase O2 demand and
appears to cause no oxidative stress.
3.2 Behavioural Analysis
3.2.1. Flicking rate
Exposure to EMF caused a slight increase in
antennular flicking rate in small and medium
Helmholtz
L-Lactate
D-Glucose
EMF
Control
EMF
Control
0h
1.21±0.33
2.23±0.59
0.24±0.04
0.31±0.06
2h
1.35±0.25
1.81±0.45
0.47±0.04
0.46±0.06
4h
1.05±0.22
1.47±0.39
0.72±0.7
0.73±0.07
6h
1.03±0.23
1.22±0.47
0.81±0.08
0.71±0.08
N
20
20
20
20
Table 2 L-Lactate and D-Glucose concentrations (mM) for the Helmholtz (2.8mT) trials (Mean ± SEM).

crabs although this was not statistically
significant (Fig. 5). The average pre-EMF
flicking rate of 22±4 flicks/min remained
unchanged during exposure to EMF (24±4
flicks/min). The mean flicking rate in the first
minute of exposure to EMF (25±4 flicks/min)
remained unchanged from initial
measurements in control conditions (25±4
flicks/min).
3.2.2. Activity level
During day conditions, there was no significant
difference in activity levels between EMF
exposed crabs and control, with size being the
only significant factor (p<0.05) (Fig. 6). The
decrease in activity level corresponds with an
increase in crab size, with small crabs
(19.6±2.5%) having higher activity levels than
large crabs (10.1±3.2%). During night
conditions, there was a significant increase in
activity levels for all size groups (p<0.05). Small
(42.7±5.6%) and medium crabs (45.5±5.1%)
Fig. 5. Antennular flicking rate (Mean ± SEM) of
individuals exposed to EMF and control
conditions for the three size groups (N=30) and
combined.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0h 4h 8h 24h
D-Glucose concentration (mM)
D-Glucose concentration
2.8 mT EMF 40 mT EMF Control
*
*
*
*
Figure 3.
Figure 3. L-Lactate over a 24-hour period during
control conditions and exposure to low strength
(2.8mT) and high strength (40mT) EMF. The L-
Lactate circadian rhythm was disrupted by exposure
to 2.8mT EMF and did not follow the usual trend,
showing a continuous decrease and significantly
lower values after 24 hours. The L-Lactate circadian
rhythm was altered during exposure to 40mT EMF
resulting in much lower concentrations after 4h and
8h despite following the same trend found in the
control results. Values are presented as Mean ±
SEM, * is the significance from 0h within respective
treatments (p<0.05).
0
10
20
30
40
50
Total Small Medium Large
Size
Flicking Rate (flicks/min)
Flicking Rate
EMF CT
Figure 4.
Figure 4. D-Glucose concentration over a 24-hour
period during control conditions and exposure to
low strength (2.8mT) and high strength (40mT)
EMF. D- Glucose levels followed similar circadian
rhythm in control and 40 mT EMF exposed crabs,
with significant increase towards peak locomotor
activity, while 2.8 mT exposed crabs were lacking
this increase and showed no significant elevation
after 8 h. Values are presented as Mean ± SEM, *
is the significance from 0h within respective
treatments (p<0.05).
*

had significantly higher activity levels than
large crabs (25.9±2%).
3.2.3. Side selection
Under control conditions crabs spent
significantly more time on one side of the tank
in both day (32-68±5.9%)(p<0.05) and night
(36-64±3.2%)(p<0.05) conditions (N=96).
When there was an EMF present there were no
clear preferences made between sides during
both day (44-56±5.9%) and night (50-50±4.4%)
conditions (N=99). There was a significant
difference between control and EMF exposed
crabs’ mean side selection for both day
(p<0.05, N=77) and night (p<0.05, N=118). This
shows that in the presence of an EMF
individual crabs fail to make a clear side
preference.
3.2.4. Shelter selection
3.2.4.1. Single shelter
The mean time spent in the shelter (48%) and
out (52%) was approximately equal in the
control trials (Fig. 7B). When there was an EMF
present in the shelter the proportion of mean
time spent within the shelter increased to 69%
(Fig. 7A). These trials also confirmed what was
discovered in the dual shelter set ups in that
the percentage time spent roaming the tank
significantly decreases from 52% in the control
to 31% when there was an EMF present
(p<0.05). The overall mean percentage time
spent in both locations was significantly
different between control and EMF conditions
(p<0.001).
3.2.4.2. Dual shelter
Under control conditions the mean time spent
in each shelter and out roaming in the tank
were equal (35% EMF shelter, 31% CT shelter
and 34% No shelter) (Fig. 7D). During EMF
exposure, there were clear preferences for the
shelter with the EMF present resulting in 69%
mean time spent within, with only 9% spent in
the control shelter and 22% spent roaming the
tank (Fig. 7C). There was a drop in mean time
from 34% under control conditions to 22%
during EMF exposure suggests that once the
crabs detect EMFs they will begin to seek
shelter and are drawn to the shelter with the
EMF emanating from within. The overall mean
percentage time spent in all three locations
was significantly different between control and
EMF conditions (p<0.001). Throughout all
0
10
20
30
40
50
60
Total Small Medium Large Total Small Medium Large
Size Size
Day Night
Activity level (%)
Activity level
EMF Control
Fig. 6. Activity level (Mean ± SEM) of the different size groups in both treatments for day and
night conditions. (NDAY=79, NNIGHT=117).

shelter trials an equal number of male and
female crabs were used. There were no
significant differences in behaviour between
the sexes.
4. Discussion
4.1. Physiological Analysis
4.1.1. Haemolymph parameters
L-Lactate and D-Glucose both followed a
natural circadian rhythm with a rise in D-
Glucose, and a subsequent fall in L-Lactate
concentrations throughout the day. L-Lactate
levels rise throughout the night due to
increased activity and subsequent increase in
glucose metabolism. In crustaceans,
haemolymph glucose and lactate levels are
affected by various environmental conditions
and stressors (Kallen et al. 1990; Reddy et al.
1996; Chang et al. 1998) and should cycle
together under normal, unstressed conditions.
L-Lactate is an indicator of anaerobic
respiration, typically due to impaired gill
function or hypoxic conditions (Durand et al.
2000). D-Glucose, the primary fuel for ATP
production in crustaceans is crucial in
maintaining metabolic processes (Barrento et
al. 2010). D-Glucose levels show a negative
correlation with vigour where healthy
individuals have lower levels and moribund
crabs become hyperglycaemic (Barrento et al.
2010). Activity levels in crabs should partially
be reflected in D-Glucose concentrations
(Briffa and Elwood 2001). D-Glucose levels
were found to correlate well with current
literature in that there was a continual rise in
concentration in relation to locomotor activity
(Hamann 1974; Reddy et al. 1981; Kallen et al.
1988; Kallen et al. 1990; Tilden et al. 2001).
This suggests that D-Glucose levels continually
rise throughout the night until peak locomotor
activity has been reached during which the
levels will begin to decrease back to original
values. EMF exposure did not significantly
influence activity level which is consistent with
minor changes in D-Glucose levels. Several
studies have shown that EMF can alter the
circadian rhythm of animals through altering
melatonin levels (Reiter 1993; Schneider et al.
1994; Levine et al 1995; Wood et al. 1998).
Melatonin, a neuropeptide, present in
crustaceans, can cause shifts in L-Lactate and D-
Glucose cycles (Tilden et al. 2001). This
suggests that exposure to a field of 2.8mT
could affect melatonin secretion, which
consequently alters L-Lactate and D-Glucose
circadian rhythms. At 2.8mT, the L-Lactate
concentration follows the circadian rhythm
Fig. 7. Effect of EMF on shelter selection. Time
spent in single shelter and outside of the
shelter, if exposed to EMF (A) and when the
magnets are switched off (B). EMF (N=11) and
control (N=11). Time spent in each shelter and
outside the shelters, when one of the shelter is
exposed to EMF (C) and if none are exposed (D).
EMF (N=15) and control (N=15) Shown as a
percentage of total trial time (%).
31%
69%
EMF
52%
48%
Dual shelter selection Single shelter selection
Control
34%
31%
35%
D
22%
69%
9%
C
No shelter EMF shelter Control shelter
A B

and decreases throughout the day when
activity levels are generally lower. During the
night there were no differences in activity
levels between 2.8mT and control crabs,
however there were no increases in L-Lactate
levels.
The suppression of the rise in L-Lactate
prevents the increase in O2 affinity of
Haemocyanin that would naturally occur
(Sanders and Childress 1992). An increase in L-
Lactate has been shown to occur in Carcinus
maenas during emersion when the crabs
would be relying on anaerobic respiration.
During re-immersion L-Lactate levels remained
elevated after 1 hour suggesting that the crabs
have to repay an oxygen debt (Simonik and
Henry 2014). Exposure to EMF supresses the
rise in L-Lactate which enables the crabs to
repay the oxygen debt accrued during periods
of higher activity. During long exposures to
EMF, crabs may be unable to repay this oxygen
debt, potentially leading to increased
mortality. Both D-Glucose and L-Lactate
concentrations show high individual variability
with D-Glucose levels influenced by individual
status and reactions to external stimulus
(Matsumasa and Murai 2005). The values
observed for L-Lactate and D-Glucose
corresponded with those found in previous
literature (Watt et al. 1999; Lorenzon et al.
2008; Barrento et al. 2010; Barrento et al.
2011). Haemocyanin, as the primary oxygen
carrying protein in invertebrates, has been
shown to increase in concentration during
periods of hypoxia (Hagerman et al. 1990). The
lack of deviation in concentrations observed
suggests that EMF exposure does not elicit
similar physiological responses as hypoxic
conditions. The overall lack of change on these
parameters suggests this species can maintain
homeostasis during exposure to high strength
EMFs.
4.1.2. Respiration
Although increased oxygen demand and high
gill ventilation rates typically occur in
crustaceans subjected to different stressors
(Jouve-Duhamel and Truchot 1985; Paterson
and Spanoghe 1997), EMF (2.8mT) did not
significantly alter the respiration rate of
juvenile crabs. Respiration rates in Cancer
pagurus are highly variable due to the
alternating periods of apnoea and bradycardia
that have been observed in pausing behaviour
(Bottoms, 1977; Burnett and Bridges, 1981).
This pausing behaviour will alternate but can
be present for significant periods of time. This
was concluded by Burnett and Bridges (1981)
when individuals were found to be exhibiting
pausing behaviour for 40-50% of the time.
These results show that juvenile Cancer
pagurus respiration levels correlate well with
other species of crabs of similar size: velvet
swimming crab, Necora puber, (0.21 ±0.119 mg
O2/g/h (Small et al. 2010)); spider crab, Hyas
araneus, (0.025 mg O2/g/h (Camus et al.
2002)); Dungeness crab, Cancer magister,
(0.044 mg O2/g/h (Johansen et al. 1970)) and
shore crab, Carcinus maenas, (0.036 - 0.126 mg
O2/g/h (Newell et al. 1972; Taylor and Wheatly
1979). Current respiration values for adult
Cancer pagurus found in the literature are
28.03mg O2/g/h during pre-pause and 4.42 mg
O2/g/h post pause (Bradford and Taylor 1982).
4.2. Behavioural Analysis
4.2.1. Flicking rate
The lack of deviation in the number of
antennular flicks during initial exposure and
throughout the trials suggest that the
antennules may not be utilized in the detection
of EMF in this species, or as a reliable indicator
of detection. Similar results were reported by
Woodruff et al. (2013) after exposing
Dungeness crab, Metacarcinus magister, to a
3mT EMF.
4.2.2. Activity level

Exposure to EMF did not have any effect on the
overall activity level in Cancer pagurus. This
suggests that if there is a behavioural change
during exposure to EMF it may be more subtle
than basic movement levels. The side selection
results confirm that there is a decreased ability
to find a suitable resting spot, however the
crabs did not have higher activity levels within
the EMF treatment. Under control conditions
the crabs alternated their time between
resting and roaming, subsequently spending
larger amounts of time resting in the same
spot. EMF exposure did not affect the resting
and roaming behaviour but appeared to inhibit
the crabs from spending large amounts of time
in the same location. Overall activity levels
were not affected by EMF exposure, but the
distribution of time spent in specific locations
(see 4.2.3.) within the tank and between
resting and roaming behaviours were. The low
activity levels during the day could be a result
of behaviour consisting largely of shelter
seeking (Chapman and Rice 1971; Hockett and
Kritzler 1972; Hazlett and Rittschof 1975; Hill
1976). The discrepancies between size groups
could be explained by smaller crabs typically
inhabiting the sub-littoral zone where there
will be higher risks of predation and higher
competition for food and shelter, whereas
larger crabs which tend to be found in deeper
waters may not be subjected to the same
pressures as the juveniles given their larger
size (Paine 1976). The increase in activity levels
during the night corresponds with this species’
nocturnal behaviour and will be due to
foraging or potential mate seeking (Seed 1969;
Skajaa et al. 1998). The increase in antennular
flicking rate of larger crabs combined with the
decreased activity levels suggest that adult
crabs rely more on chemical sensing than
physical exploration to survey the
environment.
4.2.3. Side selection
Exposure to EMF does not affect the activity
levels of the crabs but affects their ability to
select a site to rest. This may be explained by
crabs seeking shelter (see 4.2.4 below) when
they detect EMF as opposed to natural
movement patterns (Skajaa et al. 1998)
observed in those within the control group.
The crabs under control conditions spent a
higher percentage of their time on one side of
the tank interspersed with active roaming.
EMF exposure inhibited a clear side preference
within the tank which resulted in an
approximately 50-50% split across the tank,
potentially reflecting shelter seeking
behaviour. Cancer pagurus has been shown to
inhabit pits when inactive (Hall et al. 1991) and
were observed spending large amounts of time
resting during the day in acclimation tanks with
minimal movement. This behaviour appears to
have been altered by exposure to EMF.
4.2.4. Shelter selection
During the single shelter trials when crabs
were exposed to control conditions there was
an equal amount of time spent inside and
outside the shelters. The same pattern was
recorded during the dual shelter trials, with an
equal amount of time spent in either of the
shelters and roaming the tank. This suggests
that when there are no environmental
stressors present the crabs will spend a portion
of their time resting in shelter and an equal
portion of their time surveying their
environment exhibiting roaming behaviour.
When there was an EMF present the amount
of time spent exhibiting roaming behaviour
significantly decreased in both single and dual
shelter trials. This has clear implications on the
Cancer pagurus population in the areas
surrounding MREDs. If there is an EMF present
then crabs will be drawn to the source of the
emission and spend significant amounts of
time within the affected area. This will come at
the cost of time spent foraging for food,
seeking mates and finding shelter, potentially

leading to higher predation rates, increased
death due to starvation and/or decreased
number of successful matings. Many offshore
sites have introduced no-take zones around
turbine arrays, with speculation that the
decrease in fishing pressure, combined with
the addition of artificial reefs in the form of
scour protection blocks, could enhance the
overall crustacean population (Langhamer and
Wilhelmsson 2009) by providing refuge and
breeding areas. However, this experiment
highlights the potential lack of spill-over effect
from these areas due to a high attraction to the
emitted EMF. This suggests that fishing zones
in close proximity to subsea power cables
could potentially see an overall decrease in
crab numbers. Scour protection zones are
estimated to create 2.5 times more habitat
than is lost by array installation (Linley et al.
2009) and with the inclusion of drilled holes
have an estimated carrying capacity of
65,000kg of fish per year per turbine (Linley et
al. 2009). If specific habitat requirements are
considered for individual target species around
MREDs during the construction of these
artificial habitats, then abundance and
diversity of associated species, including
commercially important species, could be
enhanced (Bortone et al. 1994; Kawasaki et al.
2003) subject to EMF emission mitigation.
5. Conclusion
Several decapod crustaceans are known to be
magneto sensitive, yet information available
on the effects of electromagnetic fields
emitted from MREDs is scarce. The aim of this
study was to fill some of these knowledge gaps.
Exposure to electromagnetic fields, of the
strength predicted around sub-sea cables, had
significant physiological effects on Cancer
pagurus and changed their behaviour. EMF
disrupted the circadian rhythm of
haemolymph L-Lactate and D-Glucose levels.
Melatonin levels in several species have been
found to be affected by EMF exposure. This
suggests that EMF exposure could affect
crustaceans on a hormonal level. Further
studies are needed to understand the
underlying mechanism responsible for
disrupted glucose and lactate cycles.
In this study it was shown that EMF exposure
altered behaviour, with crabs spending less
time roaming around the tank and more time
in a shelter in direct contact with the EMF. This
suggests that the natural roaming behaviour,
where individuals will actively seek food
and/or mates has been overridden by an
attraction to the source of the EMF. When
given the choice between a shelter exposed to
EMF and one without exposure, the crabs were
always drawn to the EMF. These results predict
that in benthic areas surrounding MREDs,
where there is increased EMFs, there will be an
increase in the abundance of Cancer pagurus
present. This potential aggregation of crabs
around benthic cables and the subsequent
physiological changes in L-Lactate and D-
Glucose levels, brought about by EMF
exposure, is a cause for concern.
Berried female Edible crabs move offshore and
spend 6-9 months, buried with minimal
movement and lower feeding rates
(Williamson, 1900; Edwards, 1979; Howard,
1982; Naylor et al., 1997). Given this species’
proven attraction to EMF sources, incubation
of the eggs may take place around areas with
increased EMF emissions. Long term studies
are needed to investigate the effects of chronic
EMF exposure. The effects of EMF on egg
development, hatching success and larval
fitness are unknown and need to be addressed.
As larval stages are critical population
bottlenecks, any negative effect of EMF on
crab larvae will have a drastic effect on the
edible crab fishery.
With the recent large scale renewable energy
developments, it is clear more research is
needed to reduce uncertainty of the
environmental effects of these activities on
benthic marine species, particularly on other

commercially and ecologically important
decapod crustaceans. This is important to
develop an understanding of population level
consequences and cumulative impacts of
MREDs’ stressors. These knowledge gaps need
to be addressed before the implementation of
the many approved wind farm sites around the
UK to help mitigate an ever growing problem.
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