ArticlePDF Available
Highlights
The use of submarine power cables will increase due to the growth of the marine
renewable energy sector
Installation increases noise, pollution, turbidity and physical disturbance
Operation produces electromagnetic fields, heat, entanglement risk, pollution
and reef/reserve effects
Overall impacts on ecosystems are considered minor or short-term
Uncertainties remain, particularly concerning the impacts of electromagnetic
fields
Graphical abstract
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Title
A review of potential impacts of submarine power cables on the marine environment: knowledge gaps,
recommendations and future directions
Authors
Bastien Taormina a,b, Juan Bald c, Andrew Want d, Gérard Thouzeau e , Morgane Lejart a, Nicolas Desroy f,
Antoine Carlier b
Affiliations
a France Energies Marines, 15 rue Johannes Kepler, Technopôle Brest Iroise, 29200 BREST, France
b Ifremer, Centre de Bretagne, DYNECO - Laboratoire d’écologie benthique, ZI de la Pointe du Diable -
CS 10070, 29280 Plouzané, France
c Marine Research Division. AZTI-Tecnalia. Muelle de la Herrera, s/n. 20110 Pasajes (Gipuzkoa), Spain
d International Centre for Island Technology Heriot-Watt University, Stromness, Orkney, United
Kingdom
e CNRS-UBO, IUEM, UMR 6539 - LEMAR, Technopôle Brest-Iroise, 4 rue Dumont d’Urville, 29280
Plouzané, France
f Ifremer, Laboratoire Environnement Ressources Bretagne Nord, 38 rue du Port Blanc, 35801 Dinard,
France.
Corresponding author
Bastien Taormina, bastien.taormina@france-energies-marines.org , Ifremer, Centre de Bretagne,
DYNECO - Laboratoire d’écologie benthique, ZI de la Pointe du Diable - CS 10070, 29280 Plouzané,
France
Abstract
Submarine power cables (SPC) have been in use since the mid-19th century, but environmental concerns
about them are much more recent. With the development of marine renewable energy technologies, it is
vital to understand their potential impacts. The commissioning of SPC may temporarily or permanently
impact the marine environment through habitat damage or loss, noise, chemical pollution, heat and
electromagnetic field emissions, risk of entanglement, introduction of artificial substrates, and the
creation of reserve effects. While growing numbers of scientific publications focus on impacts of the
marine energy harnessing devices, data on impacts of associated power connections such as SPC are
scarce and knowledge gaps persist. The present study (1) examines the different categories of potential
ecological effects of SPC during installation, operation and decommissioning phases and hierarchizes
these types of interactions according to their ecological relevance and existing scientific knowledge, (2)
identifies the main knowledge gaps and needs for research, and (3) sets recommendations for better
monitoring and mitigation of the most significant impacts. Overall, ecological impacts associated with
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SPC can be considered weak or moderate, although many uncertainties remain, particularly concerning
electromagnetic effects.
Keywords
submarine power cables; marine renewable energy; environmental impacts; ecosystem functioning;
benthic habitats
Abbreviations
HVDC, High-Voltage Direct Current; SPC, Submarine Power Cable; DC, Direct Current; AC, Alternating
Current; MRE, Marine Renewable Energy; SPL, Sound Pressure Level; HVAC, High Voltage Alternating
Current; EMF, Electromagnetic Field
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1. Introduction
In 1811, a powered cable was laid down across the Isar River in Germany. This is considered to be
the first underwater power cable in the world. More than a century later, the first commercial High
Voltage Direct Current (HVDC) cable, installed in 1954 in the Baltic Sea, linking Sweden and Gotland
Island. Since then, submarine power cables (SPC), using direct current (DC) or alternating current (AC),
have continued to spread across the globe. Technologies have improved with respect to materials, cable
length and width, and installation techniques. Applications of SPC are numerous: they can be used to
connect autonomous grids, to supply power to islands, marine platforms or subsea observatories, and to
convey power generated by marine renewable energy (MRE) installations to electrical sub-stations. While
most SPC are on top of or buried within the seafloor, some (known as dynamic cables) are deployed
through the water column between the surface and the seafloor. This last category of cables is used for
offshore oil platforms and, recently, to export energy produced by floating MRE devices (like wind
turbines), a technology still under development. In 2015, almost 8000 km of HVDC were present on the
seabed worldwide, 70% of which were in European waters. In comparison, the total length of all
submarine cables deployed (including AC and DC power cables and telecommunication cables) is of the
order of 106 km [1].
SPC, like any other man-made installation or human activity at sea, may cause disturbances to
marine life and habitats. When talking about anthropogenic disturbances, it is important to distinguish
‘effects’ from ‘impacts’. According to the framework proposed by Boehlert and Gill [2], effects are
modifications of environmental parameters (or “stressors”), such as the substrate type, hydrodynamics,
water temperature, noise, or electromagnetic fields beyond the range of natural variability. Impacts
correspond to changes observed at “receptor” level, i.e., the different ecosystem compartments (biotopes,
biocenosis), or levels (community, populations) or some ecological processes within marine ecosystems
(trophic interactions). Impacts may be positive or negative, although this distinction remains subjective.
Scientific interest in interactions between marine life and submarine cables started with the first
records of cable damage caused by whale entanglements (16 events between 1877 and 1955; [3]) or by
fish and shark bites (at least 39 events from 1907 to 2006; [4]). Although such events have decreased
significantly with technological improvements (cable burial and advances in design or protection; [5]),
ecological concerns remain. Nowadays, ecological issues refer not only to direct physical interactions
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between large animals and cables but also to less obvious impacts of cables on marine communities and
habitats.
Numbers of SPC will increase drastically in coming decades with increasing grid connections of
islands and archipelagos and the development of MRE projects (offshore wind farms, tidal and wave
turbines). Several inter-governmental organisations have set objectives for the next decades. For example,
in 2014, the European Council set 27% as a target for the minimum proportion of total electricity
consumption produced by renewable energies in the EU by 2030 (EUCO 169/14). In 2008, the global
electric energy supply produced by all grid-connected renewable energy installations taken together was
estimated at 12.9%, and several predictions estimate an increase to 17% by 2030 and 27% by 2050 [6].
Despite more than 10 years of scientific work on potential environmental impacts of MRE
projects [7,8], SPC have received much less attention than MRE devices themselves. Indeed, only nine
published papers focusing on in situ effects or impacts of SPC were found during the literature research.
These studies addressed the impacts of SPC on benthic communities, considering both installation or
operation phases [9–13], examined communities colonising unburied structures [12,14], and/or reported
species-specific changes of behaviour [15–17]. Considering the current exponential increase in SPC
worldwide, a robust and accurate assessment of their potential environmental impacts has become a
priority.
In this context, the aims of the present study are (1) to review the existing knowledge concerning
potential ecological impacts from SPC during installation, operation and decommissioning phases, (2) to
attempt to hierarchize these impacts according to their significance and (3) to point out knowledge gaps
and recommendations for monitoring and mitigation of these impacts.
2. Methods
A literature search was conducted using online databases and internet search tools (Web of Science,
Science Direct, Google Scholar, ResearchGate) to create a bibliographic database including peer-
reviewed scientific publications, books, theses and non-peer-reviewed consultancy and technical reports.
Owing to a general lack of published studies, a large proportion of current knowledge comes from
industrial or governmental reports and environmental impact assessments that may have associated
confidentiality issues. The literature search first focused on publications about SPC generalities and their
global environmental impacts before targeting specific literature for each of the different identified
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impacts. Documents focussing on anthropogenic disturbances other than SPC, but potentially inducing
comparable impacts (e.g., artificial reefs or sediment reworking for example) were also considered. Based
on the main conclusions of the reviewed literature, the relative importance of the different potential
impacts and the associated scientific uncertainty was compiled.
3. Features of submarine power cables
3.1 Technical characteristics
SPC are specifically designed to relay electric currents either as Alternating Current (AC) or
Direct Current (DC), the transmission type being determined by the capacity and length of the
transmission line, as well as commercial issues. For example, a DC line can transmit more power than an
AC line of the same size, but is more expensive. AC transmission presents some limitations since the
reactive power flow due to the large cable capacitance causes power loss, which then limits the maximum
transmission distance (<100 km). DC is therefore the only viable technical option for long distance cable
links. AC is more frequently used within grids of marine renewable energy devices [8]. Cables in use
today include monopolar, bipolar and three-phase systems. SPC diameters are between 5 and 30cm and
weigh between 15 and 120 kg m-1 (including stabilization devices such as articulated steel shell).
Different methods exist to insulate electric cables in order to contain the emitted electric fields. Specific
designs have been addressed for dynamic cables, with specific armouring layers and internal components.
Indeed, their high position in the water column makes them more susceptible to fatiguing pressure and
twist caused by hydrodynamics (particularly swell). Table 1 describes most types of recently installed
SPC.
3.2 Cable installation
Before any deployment, the cable route must be chosen, depending on the bathymetry, seabed
characteristics and economic activities of an area. The route must first be prepared, sometimes with
adjustment of the slope and depth, or removal of obstacles before the passage of the cable-laying device.
An example of an established method is the pre-lay grapnel run, consisting of dragging a hooking device
at low speed along the planned route to remove any material, such as abandoned ropes or fishing nets.
Cable deployment is a complex process requiring highly specialised equipment. Cables are
usually buried within the seafloor by different techniques including trenching with a cutting wheel in
rocky sediments and ploughing or water jetting in soft sediments (Figure 1; [18]). Ploughing generally
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allows trenching, laying the cable and burying it with the extracted sediment in a single operation. Special
backfill materials for burial can be required when burial is technically complicated. In the case of hard or
deep bottoms, the cable can simply be laid on the seafloor and stabilised with suitable cover. The duration
of the cable installation process determines the magnitude of some environmental effects, such as
increased turbidity or anthropogenic noise. The duration of installation can be highly variable according
to methods and seafloor characteristics, as cable laying is much more difficult for a route with obstacles
such as boulders, rocks or outcrops, compared with a featureless seafloor [18]. The rate of cable-laying
may vary from 0.13─0.21 km h-1 for a cable buried using water jetting to 1.85 km h-1 for a cable that is
simply laid down [19]. For cable burial in the upper intertidal zone, the trench is often dug with more
common devices such as mechanical excavators, and directional drilling is sometimes employed.
3.3 Cable protection
Depending on anthropogenic and natural perturbations in the route area, the cables may need to
be protected from damage caused by fishing gear or anchors [19], strong hydrodynamic forces or storms.
When trenching is not possible, other methods exist for unburied cables, such as rock-mattress covering,
cable anchoring, ducting, cast-iron shells, concrete slabs, steel plates or dumped rocks [19]. On uneven
seafloors, the cable may form “free spans” along its route where it will hang without touching the
seafloor. This may promote vibration, chafing, fatigue and, ultimately, cable failure [18]. One solution is
to fill the empty space between the cable and the seafloor with rock dumping or concrete bags. As an
example of protection methods employed, the cable connecting the French tidal turbine test site of
Paimpol-Bréhat to the land was installed on a highly hydrodynamic and hard seafloor (rock and pebbles).
The cable is unburied over a large portion of its route but is protected with cast-iron shells and concrete
mattresses (Figure 2); the free spans are filled with concrete bags. In addition to these different protection
methods, authorities typically create a protected area encompassing the cable route, with prohibition of
other human activities (fishing, anchoring, dredging, etc.) in order to protect the cable from damage.
4. Environmental effects and impacts
Potential environmental effects associated with SPC are summarised in Figure 3. During installation,
maintenance and decommissioning phases, these effects may include physical habitat disturbances,
sediment resuspension, chemical pollution and underwater noise emission. More long-term effects may
occur during the operational phase, with changes in electromagnetic fields, heat emission, risk of
entanglement, chemical pollution, and creation of artificial reef and reserve effects.
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4.1 Habitat reworking
Physical changes
Substratum alterations are mainly created by equipment used for cable route preparation (grapnels such as
in the aforementioned Pre-Lay Grapnel Run) and installation of the cable (ploughing, jetting and cutting-
wheels). The surface area of disturbance can be enlarged when installation techniques require large ships
with several anchoring stabilizers [18].
These methods of reworking the seabed may lead to direct destruction of benthic habitats, flora
and fauna. However, such effects are usually restricted to a limited area, the width and intensity of
disturbance, depending on the installation method. For example, the footprint of a trenching plough may
vary from 2 to 8 m depending on device size [5]. According to Vize et al. [20], ploughing methods seem
to cause less seabed disturbance than other methods. These disturbances are usually limited in time, as
installation works only require a few hours or days per km of cable [21]. Ploughing and jetting methods
favour a quicker recovery of bottom topography, as the trench is filled with displaced and re-suspended
material immediately after digging and cable laying. In intertidal areas, physical impacts on the substrate
usually occur over a larger surface area, of the order of tens of metres, due to the utilisation of vehicles
such as mechanical excavators (Figure 4). Alternatively, underground horizontal directional drilling (10 m
below the sediment surface) may be used in intertidal areas up to distances of 700-1000m, and
occasionally up to 1800 m [18]. This installation technique only disturbs the substrate and biota locally
over a few m² at the land and sea entrance points.
Unburied cables may also cause habitat loss, but to a lesser extent than buried cables.
Disturbance is limited to the cable width itself, or to the dimensions of the materials used to stabilise and
protect [22]. In shallow areas, some sections of unstabilised, unburied cables may act as dragging
elements that disturb the sediments due to their strumming movement induced by the swell during the
operation phase [23]. Wave action may shift the cable, and direct interaction with the hard seafloor can
result in surface scraping and incisions in rock outcrops [13]. Maintenance (to a lesser extent) and/or
decommissioning phases may generate similar effects to those of installation, but their magnitude will
depend on the duration and scale (repairs vs. inspections) of the works.
With respect to other human activities at sea, physical disturbance to the seabed caused by cables
is spatially limited. For example, the footprint of submarine cables in the UK coastal area is about 0.3
km2, representing less than 0.01% of the coastal seabed [24], whilst in the Basque Country coastal zone
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(Northern Spain), the footprint of cables and pipelines is about 2.3 km2, or 0.02% of the area between the
coastline and the exclusive economic zone [25].
Biological changes
Substratum alterations may affect related benthic communities by direct impacts such as
displacement, damage or crushing of organisms. Andrulewicz et al. [10] examined the environmental
impact of the installation of a buried submarine power cable on soft bottoms of the Baltic Sea. They
concluded that there were no significant changes in benthic diversity, abundance or biomass on the cable
route or in its close proximity one year after the installation.
The magnitude and significance of biological changes depend on several factors linked to the
sensitivity and resilience capability of the species or communities affected. Habitat or community
resilience is characterised by the capacity to return to its initial ecological state after a perturbation
(cabling in this case), and the the duration of this response. The weaker the resilience is, the more
sensitive the habitat or the community. Thus resilience depends on several factors, including: the nature
and stability of the substratum [26–28], habitat depth [24,29] and life cycle of disturbed species (for
example, seagrass meadows, which grow very slowly, may take several years to recolonise a disturbed
area [30]).
The magnitude of biological changes is also dependent on the composition of the community
itself, i.e., the relative occurrence of benthic species (abundance and biomass) and assemblages (richness)
along the cable route, compared with their occurrence at the regional scale. Due to the small spatial
footprint of cabling, the overall impact on benthic communities is negligible if its spatial distribution is
significantly homogeneous.
Benthic community resilience after commissioning of submarine cables remains poorly
understood owing to the lack of long-term studies (i.e. occurring several years). Despite the relatively
small spatial footprint affected by SPC operations, future studies should focus on the resilience of habitats
and communities of particular ecological or economic interest (e.g. sea grass, maerl beds and nursery
areas).
4.2 Sediment resuspension
Depending on the nature of the seafloor, sediment reworking by installation, maintenance or
decommissioning can lead to turbid plumes that can reach several tens of hectares, with suspended
particulate matter concentrations that can reach several dozen mg l-1 [31]. Apart from sediment type, the
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extent and properties of plumes will depend on factors such as installation technique, hydrodynamic
conditions and the scale of cable-laying. For instance, in the Nysted offshore wind farm (Denmark) where
the substrate is dominated by medium sand sediment, cable installation in water depths between 6 and
9.5m, generated mean particle concentrations of 14 mg l-1 (up to 75 mg l-1) at 200 m from the operation
site during trenching with a backhoe dredger, and 2 mg l-1 (up to 18 mg l-1) during jetting (Seacon, 2005 in
[20]) . Turbidity can persist for several days depending on the duration of the whole cable-laying process.
At the Nysted offshore wind farm, one month was necessary to excavate 17,000m3 of sediment for a 10.3-
km long, 1.3-m wide and 1.3-m deep cable trench [32]. However, at any given location on a cable route,
disturbance will typically persist from a few hours to a few days.
Decrease in water transparency and deposition of the resuspended material may limit light for
primary producers and impact feeding ability of fish that detect their prey visually [33]. The efficiency of
invertebrate filter-feeding could also be temporarily modified [34,35]. Resuspension/deposition processes
through the plume may bury the eggs of bottom laying species. The presence of mineral particles in the
water column may also lead to gill damage in young fish larvae [36,37]. For example, early survival of
cod recruits (whose eggs are pelagic) may be affected by the sediment plume created by cable trenching
[38].
Nevertheless, turbidity increases resulting from cable installation and decommissioning
constitute localised and short-term effects. Although no study has focused on the impact of particle
resuspension induced by cable installation and decommissioning on marine communities, it should
generally have negligible impacts on marine ecosystems.
4.3 Chemical pollution
The main chemical risk is the potential release of sediment-buried pollutants (e.g., heavy metals and
hydrocarbons) during sediment re-suspension caused by cable burial, decommissioning or repair works. The
highest contaminant concentrations are generally located in coastal areas due to human activities. A
preliminary analysis to assess the level of sediment toxicity should be performed in potentially polluted areas
to select a cable route which avoids the remobilisation and dispersion of pollutants [39].
Pollution can also occur during the operation phase, especially for monopolar DC cables using sea
electrodes for the return current path (which represent around 30% of HVDC in service use [40]). Indeed,
the cathode and the anode of sea electrodes release toxic electrolysis products like chlorine and bromine
which can impact the immediate water quality [10,40]. To a lesser extent, some older cables have
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hydrocarbon fluid insulation and may leak contaminants into the marine environment when damaged. The
amount of fluid released will vary according to the time needed to detect and repair the leakage, its location
and the extent of the damage, but in worst cases several tens of litres can be released per hour (Schreiber et al.
2004, in [41]). It should be noted that installation of oil-insulated cables ceased in the 1990s [42].
Furthermore, ships and hydraulic equipment pose a higher potential risk of accidental oil leakage during
operations [23,43]. Cables also include copper, lead and other heavy metals that are potential sources of
contamination. For example, a cable consisting of a 3.5-mm lead sheath contains 12 kg lead m-1 (Schreiber et
al., 2004 in [41]). Heavy metals can potentially dissolve and spread into the sediment from damaged and
abandoned cables, but the quantities released are considered insufficient to have significant impacts.
Furthermore, such pollution is rare as cables are usually removed when no longer in operation. Although
no studies focus specifically on SPC-related contaminants, this source of disturbance is considered to be rare,
spatially localised and unlikely to have significant impacts on benthic communities.
4.4 Underwater noise
Anthropogenic noise can be produced during route clearance, trenching and backfilling, cable
and cable protection introduction by the vessels and tools used during these operations. Intensity and
propagation of underwater noise will vary according to bathymetry, seafloor characteristics (e.g.,
sediment type and topography), vessels and machines used, and water column properties. In-situ data on
such noise is scarce, and modelling approaches have been used to estimate the sound pressure levels
(SPL) expected during installation. Nedwell and Howell [44] examined the noise produced by plough
trenching in a sandy gravel area for the installation of an electric cable within a Welsh offshore wind
farm. Results showed a maximal noise emission of 178 dB re 1μPa (on a frequency range from 0.7 to 50
kHz) at 1 m from the trenching area. A similar study by Bald et al. [45] focused on noises from trenching
and cable installation of a wind-farm platform in a sandy area in the Bay of Biscay. During the installation
phase, average sound level was 188.5 dB re 1μPa (at 11 kHz) at 1m from the source. Modelling using
these in situ data estimated that the underwater noise would remain above 120 dB re 1μPa in an area of
400 km² around the source.
Another, albeit lesser, noise emission caused by submarine cables comes from vibrations during
operation of several kinds of HVAC (High Voltage Alternating Current) cables because of the Coulomb
force occurring between conductors [46]. For example, a 138 kV transmission cable situated in Canada
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emits a SPL, for the 120 Hz tonal vibration, of approximately 100 dB re 1 Pa at 1 m [47]. Compared to
cable installation, such SPL is low, but continuous because it occurs during the whole operation phase.
There is no clear evidence that underwater noises emitted during cable installation affect marine
mammals or any other marine animal, although it is accepted that many marine animals (notably
mammals and fishes) detect and emit sounds for different purposes such as communication, orientation or
feeding. Marine mammals have high frequency functional hearing ranges from 10 Hz to 200 kHz [48],
while fish typically hear at much lower frequencies, often from 15 Hz to 1 kHz [49]. Other taxa,
organisms including sea turtles [50,51] and many invertebrates such as decapods [52], cephalopods
[53,54] or cnidarians [55] have also been shown to be sound-sensitive. Many studies highlight the
reaction of cetaceans to anthropogenic sounds of different intensities [56,57]. Sounds generated by ship
activity can impact the behaviour of different fish species [58,59]. Anthropogenic underwater noise can
affect marine life in different ways, by inducing species to avoid areas, disrupting feeding, breeding or
migratory behaviour, masking communication and even causing animal death [60]. So far,
characterisation of acoustic thresholds causing temporary or permanent physical damage are much better
described for marine mammals [61,62], than for fish [63], and remain unknown for marine invertebrates
and sea turtles [64].
Compared with other anthropogenic sources of noise, such as sonar, piling or explosions,
underwater noise linked to undersea cables remain low. Cable installation is a spatially localised
temporary event, so the impact of noise on marine communities is expected to be minor and brief. HVAC
cable vibration, although significantly lower than potential SPL during the installation phase, requires
special attention though because its long-term impacts remain unknown.
4.5 Reef effect
Like other immersed objects (e.g. shipwrecks, oil/gas platforms, and MRE devices) unburied
submarine cables and associated protection/stabilisation can create artificial reefs, inducing the so-called
‘reef’ effect [65]. Artificial reefs have been commonly used for centuries to enhance fisheries, and more
recently for habitat rehabilitation or coastal protection [66]. These structures are colonised by hard-
substrate benthic species including epifauna and mobile macrofauna, and may also attract mobile
megafauna, such as decapods or fishes.
The extent of the reef effect depends on the size and nature of the cable protection structure, but
also the characteristics of the surrounding area and native populations [65]. Such artificial structures are
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expected to have limited reef effects when located within a naturally hard substratum environment. For
example, Sherwood et al. [14], looking at the effects of laying and operating the BassLink HVDC cable,
found that, 3.5-years after the cable installation, the benthic sessile community present on the half-shell
cover was similar to the surrounding basalt reef area (Figure 5.A). Similar investigations showed no
significant differences between communities on powered cables and hard bottom control areas [9,12,67].
By contrast, on soft sediments, unburied cables generate a stronger reef effect and host a new community,
as illustrated by the unburied sections of the ATOC/Pioneer cable (Half Moon Bay, California) colonised
by actinarians [13]. In this case, sea anemones became more abundant on the cable than on the
surrounding soft bottom 8 years after cable installation (Figure 5.B) and fish species were more abundant
close to the cable, probably in response to increased habitat complexity compared with the surrounding
environment.
‘Reef effect’ is usually considered to be a positive anthropogenic impact, as artificial reefs
generally have higher densities and biomass of fish and decapod crustaceans than surrounding soft
bottoms. Also, when associated with a fisheries exclusion area (as described in section 4.6), artificial reefs
may function as refuges for these populations, with potential spill-over benefits for adjacent stocks and
fisheries [68]. This is particularly true for commercial species, like the European lobster (Homarus
gammarus) or edible crab (Cancer pagurus) observed on offshore wind-farm foundations [69,70]. In
some cases, the cable reef effect is considered a compensatory measure for habitat destroyed during cable
installation [65]. Concerning dynamic cables used to connect offshore floating MRE projects, in addition
to the processes of colonisation and concentration, biofouling can significantly increase cable weight and
wear at least on the first tens of metres, creating technical problems [71].
On the other hand, reef effect may potentially result in long-term negative effects if the structures
facilitate the introduction of non-indigenous sessile species. Indeed, the number of non-native species
present on new hard artificial substrate can be 2.5 times higher than on natural substratum [72]. Thus, the
presence of a new hard substratum, such as a cable or its protection structures, on soft sediment can
potentially open a corridor to a new area for some hard-bottom sessile species. Such processes can
potentially lead to the spread of new introduced species by a stepping stone process across
biogeographical boundaries [73]. Although cable routes are narrow and often buried in areas of soft
sediment, and no spread of invasive species caused by SPC has been documented, this question needs to
be considered in light of the exponential growth of offshore wind farms.
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4.6 Reserve effect
The potential reserve effect of SPC is linked to the limitation/interdiction by local authorities of
environmentally damaging human activities (trawl fishing, anchoring, dredging, etc.) around the cable
route during the operation phase and is considered as a positive effect for ecosystems. In some cases, the
use of passive fishing equipment (nets, lines, and traps) is permitted, reducing the protection of targeted
species. The size of the protected zone and the level of restriction depend on the cable installation method
(buried or unburied), the number of cables present in the area, and the size of the electrical connections.
For example, the Cook Strait cables have an extensive protected area to prevent damage to three
submarine HVDC cables and one fibre-optic cable which link the North and South Islands of New
Zealand over 40 km. An area seven kilometres wide around these cables, where anchoring and fishing of
any type are prohibited, was created by New Zealand authorities, corresponding to a marine protected
area of approximately 236 km² (Figure 6; [74]).
With fishing access restricted, economically exploited sedentary species (such as scallops or
clams) will be protected throughout their lives, but protection of mobile species (such as fish) will only be
effective during the time they live in/pass through the cable area. A study focusing on fish found no
significant differences in species richness inside and outside a protection zone [75]. The reserve effect has
been clearly demonstrated for some commercial offshore wind farms, including their associated electric
cable grids. Within the Dutch offshore wind farm Egmond aan Zee, where all nautical activities are
prohibited, the habitat heterogeneity [76], benthic biodiversity and possibly the use of the area by the
benthos, fishes, marine mammals and some bird species have increased (although counterbalanced by a
decreasing use of several other bird species). These changes occurred during the first two years of wind-
farm operation, in response to the establishment of the marine protected area but also other factors, such
as the reef effect of the wind turbine foundations, rockfill and cables. Nenadovic [77] studied a protected
area associated with a fibre-optic cable route on the coast of the Gulf of Maine (USA) and showed a
significant difference in epifaunal community structure between protected and unprotected areas. In
particular, engineer species were more frequent near the cable route. The maintenance of such species
with a complex biological structure highlights the structuring effect of marine protected areas.
4.7 Electromagnetic fields
The potential ecological impacts of electromagnetic fields (EMF) are of particular concern. EMF
are generated by current flow passing through power cables during operation and can be divided into
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electric fields (called E-fields, measured in volts per metre, V m-1) and magnetic fields (called B-fields,
measured in μT). Electric fields increase in strength as voltage increases and may reach 1000 μV m-1 for
an electric cable [78], but are generally effectively confined inside cables by armouring. EMF
characteristics depend on the type of cable (distance between conductors, load balance between the three
phases in the cable, etc.), power and type of current (direct vs. alternating current AC generates an
alternating magnetic field which creates a weak induced electric field of a few μV m-1, called an iE-field,
near the cable), and whether it is buried or not [8,79]. When the cable is buried, the sediment layer does
not entirely eliminate the EMF, but reduces exposure to the strongest EMF existing in direct contact with
the cable [80]. The strength of both magnetic and induced electric fields increases with current flow and
rapidly declines with distance from the cable [81].
Electric currents with intensities of 1600 A are common in submarine cables. In response,
magnetic fields of approximately 3200 μT are generated, decreasing to 320 μT at 1 m distance, 110 μT at
4 m and values similar to the terrestrial magnetic field (50 μT) beyond 6 m [82]. By contrast, according to
AWATEA [83], a standard submarine cable carrying 132 kV AC (350 A) generates a magnetic field of 1.6
μT on the “skin” of the cable (i.e., within millimetres), while cables carrying 10-15 kV DC do not
generate a significant magnetic field beyond a few centimetres from the cable surface. The magnetic field
varies greatly as a function of the cable type, and modelling of the magnetic field induced by either DC
(Figure 7.A) or AC cables (Figure 7.B) reveals this heterogeneity (1 to 160 μT at the cable surface; [81]).
Particular attention must be paid to monopolar DC cables using sea electrodes for the return current path,
the design of which leads to higher magnetic and electric fields [40,81]. Although modelling presents
serious limitations in the understanding of ecosystem-scale responses to such disturbances, the rare in-
situ EMF studies available for review yielded values of measured EMF comparable to those calculated by
modelling [10,14].
Many marine species around the world are known to be sensitive to electromagnetic fields,
including elasmobranchs (rays and sharks), fishes, mammals, turtles, molluscs and crustaceans. Indeed,
the majority of these taxa detect and utilize Earth’s geomagnetic field for orientation and migration [84–
88]. Some are electrosensitive, like elasmobranchs, which are able to detect E-fields and iE-fields through
specific organs called ampullae of Lorenzini [89,90]. This electrosense can be used to detect electric
fields emitted by prey, conspecifics or potential predators, as well as for orientation [90]. A few incidents
of bites observed on unburied SPC may also be linked to the electric field emitted by cables.
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Thus, SPC can possibly interact in a negative way with sensitive marine species, especially
benthic and demersal organisms through:
effects on predator/prey interactions,
avoidance/attraction and other behavioural effects,
effects on species navigation/orientation capabilities,
and physiological and developmental effects.
Elasmobranchs can detect very low electric fields( starting from 0.005 μV cm-1 [81]), and magnetic
(20─75 µT [82,86]). Power cables inducing a strong electric field can repel many elasmobranch species,
preventing some movement between important areas (such as feeding, mating and nursery areas). As part
of the COWRIE (Collaborative Offshore Wind energy Research Into the Environment) project, Gill et al.
[91] reported that elasmobranchs are attracted by electric fields generated by DC between 0.005 and 1 µV
cm-1, and repelled by electric fields of approximately 10 µV cm-1 and higher. Mesocosm studies
(COWRIE project) on impacts of EMF emitted by submarine cables on several elasmobranch species
showed that the response was not predictable and seemed to be species specific, maybe even specific to
individuals [92]. Teleosts, especially diadromous fish, also use natural EMF to migrate. Westerberg and
Lagenfelt [16] showed that the swimming velocity of European eel (Anguilla anguilla) slightly decreased
when crossing the electromagnetic field of a non-buried 130 kV cable, but did not report evidence of
population-scale impact. Furthermore, no substantial impacts have been shown on physiology or survival
of these taxa [93,94].
Concerning invertebrates, data are scarce except for a few studies relating to minor or non-
significant impacts of anthropogenic electromagnetic fields on benthic invertebrates [15,17,93,95,96].
However, a recent experimental study performed by Hutchison et al. [97], highlights a subtle change in
the behavioural activity of the American lobster (Homarus americanus) when exposed to EMF from a
HVDC cable.
Another noteworthy issue is that substantial data gaps exist between the interaction of pelagic
species (like pelagic shark, marine mammals or fishes) and dynamic cables. These gaps remain partly
owing to difficulties in evaluating impacts at population scale around these deployments.
4.8 Heat emission
When electric energy is transported, a certain amount is lost as heat by the Joule effect, leading
to an increase in temperature at the cable surface and a subsequent warming of the immediate surrounding
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environment [98]. Constant water flow around a laid-down or a dynamic cable tends to dissipate thermal
energy and confines it to the cable surface [18]. However, for buried cables, thermal radiation can
significantly warm the surrounding sediment in direct contact with the cable, even at several tens of
centimetres away from it, and especially in the case of cohesive sediments [99]. Heat emission is higher
in AC than DC cables at equal transmission rates. Heat emission can be modulated by physical
characteristics and electrical tension of the cable, burial depth, bottom type (thermal conductivity, thermal
resistance, etc.) and physical characteristics of the environment [19,98,99].
Despite the evidence for thermal radiation from subsea cables, very few studies exist on the
subject and most consist of numerical modelling [18,100]. One of the rare field measurement studies
concerned the offshore wind array of Nysted (maximal production capacity of about 166 MW), in the
proximity of two AC cables of 33 and 132 kV buried in a medium sand area, approximately 1m deep.
Results showed a maximal temperature increase of about 2.5 ºC at 50 cm directly below the cable [41].
Transposition of these results to other locations is difficult, considering the large number of factors
impacting thermal radiation, and other field studies are necessary to gain a better understanding of
thermal radiation effects.
Temperature increases near the cable can modify chemical and physical properties of the
substratum, such as oxygen concentration profile (redox interface depth) and, indirectly, the development
of microorganism communities and/or bacterial activity. Physiological changes in benthic organisms
living at the water-sediment interface and in the top sediment layers can also potentially occur [19,101].
Temperature radiation can potentially cause small spatial changes in benthic community structure by way
of migratory behaviour modification with cryophilic species being excluded from the cable route in
favour of other, more tolerant species.
To our knowledge, the impacts of local temperature increase caused by electric cables on benthic
communities (macrofauna diversity or microbial structure and functioning) have rarely been examined,
and in-situ investigations are lacking. Furthermore, studies using controlled temperature increases are
often unrealistic regarding the extent of suspected warming. This considerable knowledge gap prevents
drawing conclusions about ecological impacts of long-lasting thermal radiation on ecosystems, but
considering the narrowness of the corridor and the expected weakness of thermal radiation, impacts are
not considered to be significant. Nevertheless, new field measurements and experiments are required to
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fully understand this phenomenon under operational conditions and to assess its impacts on potentially
exposed organisms.
4.9 Entanglement risks
Before the 1960s, entanglement of mobile megafauna with cables occurred during the operation
phase leading, in the worst cases, to lacerations, infections, starvations and drowning of the trapped
marine mammals [102]. Technical improvements made since the 1960s for installation of laid-down
cables have reduced this risk [3]. Currently, entanglement risks only concern dynamic SPC. Although this
risk is considered to be non-significant, concerning a single dynamic SPC (such as pilot scale projects still
under development), it may require more attention in the future owing to the growth in commercial farms
of floating devices and associated webs of dynamic SPC and mooring lines hanging in the water column.
According to Kropp [103], arrays of dozens of dynamic cables and mooring lines per km² can potentially
affect large marine animals, i.e. whales.
According to existing reports, entanglements caused by dynamic SPC will remain a low risk
[103,104]. The large diameters of SPC (>5 cm) make them relatively inflexible [105], and mooring lines
and dynamic SPC should be tight enough to reduce entanglement [103]. However, indirect entanglement
resulting from discarded fishing gear wrapped around dynamic SPC [102] may significantly impact a
larger set of species, including marine mammals, sharks or fishes. Quantifying such risks will only be
possible when floating MRE installations are operational. Consequently, entanglement risk remains
highly speculative at this stage, relying on modelling data..
5. Recommendations
5.1 Mitigation and compensation measures
Potential environmental impacts of cables should be anticipated prior to the installation phase by
applying avoidance and reduction measures. In order to mitigate potential environmental disturbances
caused by cabling activity, measures exist and should be applied, including the choice of an appropriate
cable route and installation technique, answering the following:
Planning the cable route to avoid impacts on habitats and benthic species that are most sensitive to
disturbance or are of special ecological interest (with special attention to slow-growing long-lived
species). Particularly important and sensitive habitats in the North Atlantic include biogenic reefs
comprising Modiolus modiolus (Horse mussel beds), Sabellaria spinulosa (honeycomb worm), maerl
beds and Zostera seagrass meadows.
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Selecting landing zones and cable routes in order to prevent the re-mobilisation of contaminants
present in sediments and contamination of the trophic food web.
Using cable technology suitable for reducing the emission of magnetic fields, such as three-phase AC
cables and bipolar HVDC transmission systems [39], and minimising the emission of directly
generated electric fields through adequate shielding [44].
Avoiding the use of monopolar DC cables using sea electrodes, which produce toxic compounds,
generate higher EMF and accelerate corrosion of manmade structures, in favour of cable systems
with other return path options causing less disturbance [40].
Deploying dynamic SPC with the lowest risks of entanglement for marine megafauna where relevant.
Appropriate configurations, as for mooring lines [104], and appropriate cable type, with diameters
and colours allowing visual tracking of affected species [103].
Managing installations with respect to life cycles of mobile species (winter dormancy, migration,
mating and/or spawning, etc.), and to avoid disturbance of sensitive species ( e.g., fish, crustaceans,
marine mammals, marine turtles or resting/feeding birds).
Prioritizing burial depth appropriate to the substratum type. To reduce exposure of sensitive species
to electromagnetic fields and heat emission, the physical distance between animals and the cable can
be increased. According to models proposed by Normandeau et al. ([81], Figure 7), the EMF level at
the water-sediment interface with a 2m burial depth would be approximately 25% of its initial value-
versus 60% for a 1m burial depth.
Prioritizing the laid-down option rather than burying in the presence of unavoidable fragile benthic
soft bottom habitats (e.g., seagrass beds; [11]).
Installing devices with a strategy to reduce electrical connections and limiting the number of export
cables (i.e., when several MRE projects are present in close proximity).
To complement reduction and avoidance strategies, compensation measures should be considered if
residual impacts persist. In this event, and only after having addressed mitigation options, compensation
measures may be applied directly to the implantation site, or in close proximity. Discussions between
stakeholders are recommended to establish parameters for scale and responsibilities for compensation
measures.
A possible form of compensation measures can consist of improving future engineering strategies
through experimental studies of ecosystem functioning and resilience following disturbance. For example,
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on the Paimpol-Bréhat French tidal turbine test site, the cable route connecting turbines to the land
crosses important seagrass meadows containing Zostera noltei and Z. marina. In response, the prime
contractor (EDF, Electricité De France) developed an experimental protocol aiming to transplant some
seagrass plants located on the route area to another barren place before cable burial. Such measures aimed
to test transplantation techniques and acquire knowledge about the mechanism of recolonisation by
seagrass after installation of a cable [106]. Similar transplantation experiments are currently being tested
in the context of SPC installation (e.g., ongoing project by Red Eléctrica de España in Majorca and Ibiza).
Environmental monitoring strategies performed in parallel with cable installation should: (i) verify
the impact predictions made in the environmental impact study and detect unforeseen alterations, (ii)
ensure the fulfilment of mitigating measures proposed, and (iii) provide data to improve future
environmental impact assessments and installation plans [107].
5.2 Future research priorities
A hierarchical model of potential impacts based on the expected levels of ecological effects and
the associated levels of scientific knowledge (or uncertainty) is presented in table 2. This synthetic output
corresponds to a concerted expert judgement of the authors, and takes into account the main conclusions
of the literature cited in this paper. The main priorities concern benthic habitat disturbance, reef and
reserve effects and potential impacts of EMF. A substantial data gap remains concerning the impacts of
EMF because data on sensitivity thresholds or tolerance are only available for a small number of taxa.
Major uncertainties therefore remain for several large groups (cetaceans, pinnipeds, fishes, crustaceans,
and many pelagic species) [81]. Better knowledge of the different sensitivity thresholds is needed to fill
these data gaps, especially for several key species at different stages of their development. Additionally,
environmental issues may arise following industrial-scale deployment of MRE devices using multiple
submarine electric cables installed in close proximity and creating a network impacting a large area. The
cumulative effects of more than one activity or perturbation factor, which may act in synergy, must be
considered [108]. For example, recovery of benthic communities after cable installation may be slower
and less efficient if the benthic ecosystem is already threatened by other anthropogenic disturbances such
as chemical pollution, eutrophication, or invasive species (especially in enclosed and shallow areas). The
assessment of impacts due to interactions between different kinds of disturbances remains highly
speculative, partly since environmental impacts of single cables are still poorly understood.
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6. Conclusions
Although SPC have been used since the mid-19th century, environmental concerns associated with
their installation and operation are much more recent. This is due to an increased awareness of
anthropogenic impacts, the rapid expansion of SPC deployments, and the growing demand for electric
interconnections between countries that have adopted a common energy strategy.
The main potential environmental impacts associated with SPC during their operational phase are
those related to the production of electromagnetic fields, the creation of artificial reefs and reserve
effects” caused by the interdiction of certain human activities. Cable installation, maintenance and
decommissioning also impact the environment, causing direct benthic habitat modification, which can be
especially problematic in the case of sensitive bioconstructed habitats. These phases of SPC may also
induce significant particle and pollutant resuspension events in very confined and modified shallow
coastal areas. Mitigation measures are possible before, during or after projects to limit the ecological
impacts of SPC and associated maritime operations.
While potential environmental impacts generated by SPC are recognised, better knowledge of
amplitude and duration is essential. Generally these disturbances occur over short times scales, creating
relatively minor impacts on ecosystem structure and functioning. Nevertheless, the nature and amplitude
of certain impacts remain poorly studied, particularly the EMF impacts on elasmobranchs, diadromous
fishes and invertebrates, and assessment of cumulative impacts. Despite these knowledge gaps, the
present review provides a quantification and ordering of the different impacts of SPC on marine
environments and offers updated practical recommendations for developer mitigation strategies.
Acknowledgements
This work is the result of a collaborative effort between authors of the paper sponsored under EERA
(European Energy Research Alliance), UKCMER (UK Centre for Marine Energy Research), Région
Bretagne and the National Research Agency under the Investments for the Future program bearing the
reference ANR-10-IED-0006-17. The authors would like to thank Normandeau Associates Inc., Louis
Dreyfus Travocean, the Monterey Bay Aquarium Research Institute, John Sherwood and collaborators as
well as Olivier Dugornay for their kind assistance in supplying the different photography and figures. We
also thank three anonymous reviewers for constructive criticism and valuable suggestions. Finally, the
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authors would also like to thank Nolwenn Quillien, Julie Lossent, Guillaume Damblans and Kelly
Cayocca for their help.
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Figure captions
Fig 1. Wheel cutter (left); Plough (centre) and Towed Jetting Vehicle (right) (courtesy:
www.ldtravocean.com).
Fig 2. Photograph of iron shells and concrete mattresses used to protect an unburied cable at the Paimpol-
Bréhat tidal turbine test site, France (courtesy: Olivier Dugornay, 2013).
Fig 3. Diagram of the potential impacts caused by different types of SPC immersion (Dynamic, Laid-
Down and Buried) during their operation and installation/decommissioning phases.
Fig 4. Installation works of the 2000 FLAG Atlantic 1 in the intertidal area, Brittany, France (courtesy:
www.ldtravocean.fr).
Fig 5. Photographs of laid-down cables: A) the ATOC/Pioneer Seamount cable (California, USA) in an
unconsolidated sandy silt area showing three Metridium farcimen settled on the cable (courtesy: [13]); B)
the BassLink cable (Tasmania, Australia), protected by a cast-iron half-shell, showing a heavy
encrustation of algal and invertebrate species on the underlying basalt reef (courtesy: [14]); and C) the
rock mattresses used to stabilize the cable connecting the Paimpol-Bréhat tidal turbine test site, France, to
the land, showing heavy colonisation by megafauna species like the European lobster (Homarus
gammarus) (courtesy: Olivier Dugornay – IFREMER).
Fig 6. Protection zone of three SPC and one fibre-optic cable situated across Cook Strait, New Zealand.
The total protected area covers approximately 236 km² (reproduced from [73]).
Fig 7. Modelled magnetic fields at the sediment-water interface originating from different types of buried
submarine cables in operation; A: Calculated data based on 9 DC cables. B: Calculated data based on 10
AC cables (courtesy: [80]).
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65
66
Fig. 1
34
903
904
905
906
67
68
Fig 2.
35
907
908
909
69
70
Fig 3.
36
910
911
71
72
Fig 4.
37
912
913
914
73
74
Fig 5.
38
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917
75
76
Fig 6.
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920
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Fig 7.
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80
Type 1 2 3 4 5
Rated
voltage
33 kV AC 150 kV AC 420 kV AC 320 kV DC 450 kV DC
Insulation XLPE, EPR XLPE Oil/paper or
XLPE
Extruded Mass-
impregnated
Typical
applicatio
n
Supplying small
islands,
connection of
offshore wind
turbines
Connecting
islands with
large
populations,
offshore
wind parks
export cables
Crossing
rivers/straights
with large
transmission
capacity
Long distance
connections of
offshore
platforms or
wind farms
Long distance
connection of
autonomous
power grids
Maximum
length
20─30 km 70─150 km <50 km >500 km >500 km
Typical
rating
30 MW 180 MW 700 MW/three
cables
1000 MW/cable
pair
600
MW/cable
Table 1. Description of five generic submarine power cable types (Photos: 1 = General Cable; 2, 3, 4 =
Ningbo Orient Wires and Cables Co. Ltd; 5 = ABB Sweden), XLPE: Cross-Linked Polyethylene; EPR:
Ethylene Propylene Rubber (reproduced from [17]).
41
925
926
927
928
929
930
81
82
Table 2. Synthesis of the importance of potential impacts caused by Submarine Power Cables (SPC) on
different marine compartments during installation, operation, maintenance and decommissioning, based
on the author’s interpretation of the reviewed literature. For each interaction, the extent of the impact and
associated uncertainty are quantified as ‘Negligible’, ‘Low’, ‘Medium’ or ‘High’. Bur = Buried SPC; LD
= Laid-Down SPC; Dyn = Dynamic SPC. Black fill = no impact.
42
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937
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84
... While no adverse impacts around underwater cables for marine energy in particular have been observed, few in situ studies have investigated the impacts, particularly those on mobile species [14]. The lack of long-term monitoring of cables in situ can, in part, be attributed to the lack of established testing protocols and equipment and has resulted in regulatory concerns and permitting delays for marine energy projects [4]. ...
... Large knowledge gaps still exist surrounding the impacts and on marine life of submarine cables that are already in the water [14]. The development of consistent methodologies to measure the magnetic field is the first step in closing that gap. ...
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... Environmental challenges related to subsea fiber-optics and power cables have been wellresearched over the years [Taormina 2018;Jurdana, Ivce, Glazar 2014]. The main environmental effects related to subsea cables stem from the maintenance and other human operations, which causes the fragile subsea ecosystems to be harmed beyond repair. ...
... The effects may include physical habitat disturbances, the resuspension of sediments, chemical pollution and noise related to the underwater emissions. Physical changes related to the cable laying may lead to significant destructions of the seabed, as first trenches need to be created, where the cables are then laid into [Reda 2017]. This necessarily may damage the significant number of Coral reefs and other vegetation encountered in the South China Sea, and may have a significant effect on fishing and other habitation. ...
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The digital economy has led to massive changes in the economy and international trading, where user data have become the cornerstone of new business models. Digital services have become transformational and led to significant revenue generation for these corporations. However, there is a growing perception amongst individuals and governments that these digital services are not taxed fairly, given the ability of companies to shift profits between different countries. Digital service taxes have recently become very attractive and implemented in a variety of countries, but significant challenges remain. Artificial intelligence has become an attractive way of determining patterns across data and has been increasingly utilized in legal environments. I will outline a new legal framework for the integration of artificial intelligence for the determination of digital service taxes and outline the integration of subsea cable communication data into the framework. Furthermore, I will address the legal environmental challenges, specifically related to the South China Sea, and how cost associated with can be incorporated into the digital service tax environment.
... The presence of energy converters or other artificial structure at sea will create a variety of habitats available for a range of organisms (including potential non-native species -NNS), for example by providing a hard substrate for macroalgae and macroinvertebrates settlement, and attracting/aggregating organisms from higher trophic levels, such as fish and marine mammals (e.g., Langhamer, 2016;Taormina et al., 2018;Birchenough & Degraer, 2020). This artificial reef effect may aid in the recovery of benthic communities and enhance local biomass and biodiversity (e.g., Coates et al., 2014;Bender et al., 2020;, possibly leading to mitigation of potential effects caused by the activities mentioned above. ...
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This report provides research and scientific findings in EU and Members States relating to the environmental impact of the ocean energy sector. A report was compiled for each year of the ETIP Ocean 2 project and includes specific case studies or prioritised topics from D4.1 related to project deployments at sea, namely: 2019 - "Supporting ocean energy with Marine Spatial Planning"; 2020 - "Barriers and enabling factors of ocean energy consenting"; 2021 - "Environmental monitoring and modelling of ocean energy"
... Moreover, the electrical interconnections between adjacent countries are intensifying to promote the production and widespread adoption of renewable energies (European commission 2019). Accordingly, the spread of submarine power cables to support electricity transfer in rich and sensitive coastal environments is becoming a major concern, particularly regarding the introduction of artificial magnetic fields (MFs) (Petersen and Malm 2006;Taormina et al. 2018). ...
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Along European coasts, the rapid expansion of marine renewable energy devices and their buried power cables, raises major societal concerns regarding the potential effects of their magnetic field emissions (MFs) on marine species and ecosystem functioning. MFs occur at a local spatial scale, which makes sessile species the primary target of chronic and high-intensity exposures. Some of them, as ecosystem engineers, have critical functions in coastal habitats whose behavioral alteration may drive profound consequences at the ecosystem level. In this context, the present experimental study explored the effects of short exposure to direct current MFs, on the feeding behavior of a widespread ecosystem engineer, the blue mussel (Mytilus edulis). A repeated measure design was carried out with adult mussels successively exposed to control treatment (ambient magnetic field of 47 µT) and artificial MF treatment (direct current of 300 µT produced by Helmholtz coils), as measured around power cables. The filtration activity was assessed through valve gap monitoring using an automated image analysis system. The clearance rate was estimated simultaneously by measuring the decrease in algal concentration using flow cytometry. Our findings revealed that mussels placed in MF treatment did not exhibit observable differences in valve activity and filtration rate, thus suggesting that, at such an intensity, artificial MFs do not significantly impair their feeding behavior. However, additional research is required to investigate the sensitivity of other life stages, the effects of mid to long-term exposure to alternative and direct current fields and to test various MF intensities.
... Whilst standard electric field leakage (E-field) can be successfully eliminated with insulation, there is no industry standard insulation at present to prevent magnetic field (B-field) leakage [2]. Consequently, a magnetic field leaking from individual cables will create an induced electric field (iE field) through the movement of charges in seawater, the strength of which will vary depend on current strength in cables, water current speed and directions and proximities of associated cables [3][4][5]. ...
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... Wolfson et al., 1979;Harrison and Rousseau, 2020). Potential negative im-pacts include responses to noise (Wahlberg and Westerberg, 2005;Popper and Hawkins, 2019;Tougaard et al., 2020) and electromagnetic fields (EMF; Taormina et al., 2018;Hutchison et al., 2020 ) that may elicit avoidance behaviors or stress that could affect reproduction and trophic interactions. It is important, therefore, to document demersal fish and invertebrate responses to wind farm construction and operation in the US to anticipate and minimize potential impacts as offshore wind development expands. ...
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Effects of offshore wind farm (OSW) development in the US on fishery resources have been predicted based on European experience. A seven-year study of the first US OSW documented the response of demersal fish and invertebrates to construction and operation. Local fishermen and scientists designed a monthly demersal trawl survey using a Before-After-Control-Impact (BACI) design to assess potential effects of Block Island Wind Farm (BIWF), a pilot scale 30 MW project completed in 2016. Common species did not exhibit statistically significant (α = 0.10) BACI interactions in catch per unit effort (CPUE) due to BIWF operation. CPUE of structure-oriented species, such as black sea bass (Centropristis striata) and Atlantic cod (Gadus morhua), increased at BIWF following turbine installation. Fall and spring biomass varied synchronously between BIWF and a regional survey for several species including longfin squid (Loligo pealeii) and winter flounder (Pseudopleuronectes americanus). Spatial-temporal interaction between reference areas provided an estimate of the minimum effect sizes (approximately 40% to 63% among the fish evaluated) that may be considered ecologically significant when assessing potential OSW impacts. Results from this first North American OSW fisheries monitoring study provide valuable information for future OSW development on the northeastern US coastline.
... By installing marine renewable devices on such habitats, the complexity of the seafloor and surrounding water is increased with wind, wave and tidal devices functioning as an additional V. Komyakova et al. Science of the Total Environment 830 (2022) 154748 refuge for endangered species, nursery grounds and foraging areas (Glarou et al., 2020;Inger et al., 2009;Krone et al., 2017;Taormina et al., 2018). This can lead to changes in the structure of the local communities (Causon and Gill, 2018;Dannheim et al., 2020). ...
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Artificial Reefs in European Seas focuses on artificial reef research in the Mediterranean and NE Atlantic. The book describes most of the long-term projects running in European seas, presents the legal and economic issues, and suggests future uses for artificial reefs in the European context. Readership: Professionals working on or interested in the uses of artificial reefs for fishery management, coastal zone management, aquaculture and nature conservation. The case studies of reef research programmes make the book ideal for degree students studying topics in ecology, and fisheries and coastal management.
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