Wave and Tidal Range Energy Devices Offer Environmental Opportunities as Artificial Reefs

Abstract

Artificial structures such as wave and tidal energy devices provide surfaces and structures that are naturally colonised by marine flora and fauna. Properties of the building material, surface texture and structural complexity of the infrastructure will determine the suitability as a habitat for marine organisms. While it may be desirable to inhibit fouling of some parts of the energy devices, the colonisation of other features may not compromise their overall functionality. Here we explore opportunities to not just tolerate the colonisation of marine infrastructure, but to design and manipulate features that would deliberately attract and host marine organisms. Serendipitous colonisation would be transformed into deliberately creating artificial reefs on the seafloor as well as floating reefs. This paper focuses on conceptual options for coastal, close-to-shore infrastructure, and it introduces two case studies: a proposed tidal lagoon that exploits tidal range energy and a wave energy converter. Positive reef-effects of these devices could include the enhancement of biodiversity of invertebrates and fish, habitat restoration or the production of commercial species.

Full text

Wave and Tidal Range Energy Devices Offer
Environmental Opportunities as Artificial Reefs
Ruth Callaway#1, Chiara Bertelli#2, Richard Unsworth#3, Gill Lock*4, Tim Carter*5, Erik Friis-Madsen##6, Hans
Christian Soerensen##7, Frank Neumann**8
#SEACAMS2 Project, Biosciences, College of Science, Swansea University, Singleton Park, Swansea, SA28PP, United Kingdom
1r.m.callaway@swansea.ac.uk
*Tidal Lagoon Power, Pillar & Lucy House, Merchants Road, The Docks, Gloucester, GL2 5RG, UK
##Wave Dragon, Frederiksborggade 1, 1360 Copenhagen, Denmark
** Seaweed Energy Solutions, Bynesveien 48, 7018 Trondheim, Norway
Abstract— Artificial structures such as wave and tidal energy
devices provide surfaces and structures that are naturally
colonised by marine flora and fauna. Properties of the building
material, surface texture and structural complexity of the
infrastructure will determine the suitability as a habitat for
marine organisms. While it may be desirable to inhibit fouling of
some parts of the energy devices, the colonisation of other
features may not compromise their overall functionality. Here we
explore opportunities to not just tolerate the colonisation of
marine infrastructure, but to design and manipulate features
that would deliberately attract and host marine organisms.
Serendipitous colonisation would be transformed into
deliberately creating artificial reefs on the seafloor as well as
floating reefs. This paper focuses on conceptual options for
coastal, close-to-shore infrastructure, and it introduces two case
studies: a proposed tidal lagoon that exploits tidal range energy
and a wave energy converter. Positive reef-effects of these devices
could include the enhancement of biodiversity of invertebrates
and fish, habitat restoration or the production of commercial
species.
Keywords— Artificial reef, biodiversity, environmental
enhancement, wave energy converter, tidal lagoon
I. INTRODUCTION
Wave and tidal energy installations are likely to become
more frequent with the development of the marine renewable
energy market [1][2][3]. They will contribute to the general
need for coastal infrastructure such as sea-defences, harbours,
jetties and pontoons, as well as other marine energy structures,
such as oil and gas platforms. Any firm building material
added to the marine environment will potentially become an
artificial reef through colonisation by marine biota [4][5].
Structures range from small floating elements such as marker
buoys to large constructions fixed on the seafloor, for example
oil rig bases or shipwrecks [6][7][8][9]. Reef-effects occur on
different scales [10]. For off-shore wind turbines effects were
categorised into micro-scale (texture and the heterogeneity of
the building material), meso-scale (revetment and scour
protection of turbine foundation), and macro-scale (entire
wind farm footprint) [10]. Large-scale environmental
heterogeneity across locations promotes beta diversity
(variation in the composition of species communities across
landscapes) and has been shown to increase stability of
ecosystem functions [11]. Added wind-turbine infrastructure
was estimated to create 2.5 times the amount of habitat which
was lost through the placement of turbine foundations, and in
the German Bight 35 times more macrozoobenthos biomass is
concentrated in wind farm areas compared to soft bottom
locations [12][4].
Based on evidence from the off-shore wind industry a
‘Renewables-to-reefs’ concept was proposed, which followed
the rational of the US ‘Rigs-to reefs’ programme [13].
The aim of this study was to investigate the ecological
value that tidal and wave energy devices could provide. We
focused on infrastructure proposals for coastal and near-shore
waters and specifically considered tidal lagoons generating
electricity from the tidal range, as well as floating wave
energy converters (WEC) moored to the seafloor. Potential
ecosystem services (benefits to humans) were assessed, but
the core motivation of this study was to suggest design
measures for renewable energy devices which may enhance
biodiversity. While this paper concentrates on tidal lagoons
and WECs, the designs are conceptual and generic and could
be considered for other marine infrastructure projects.
II. IMPACTS ON ECOSYSTEM SERVICES
Planning and construction management is increasingly
considering environmental and socio-economic benefits of
coastal structures to minimise or mitigate ecological impacts
[14]. Reports for governmental bodies and developers provide
information and advice regarding ecological enhancement at
the planning, design and construction stages of hard coastal
structures [15][16]. Artificial structures can be beneficial and,
for example, assisted in the recovery of the dogwhelk Nucella
lapillus, whose populations had suffered from antifouling
paints [17]. On the flip side man-made infrastructure may be
utilised as a stepping stone for the distribution of invasive or
alien species, such as green algal species in the Mediterranean,
which are thought to have spread through the presence of
breakwaters [18][19][20]. Further, there are potential societal
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Proceedings of the 12th European Wave and Tidal Energy Conference 27th Aug -1st Sept 2017, Cork, Ireland
ISSN 2309-1983 Copyright © European Wave and Tidal Energy Conference 2017
2017

Fig. 1. Ecosystem services framework for the marine environment (after Turner et al. 2014 [24]).
benefits of coastal infrastructure and artificial reefs. Rigs-
to-reefs programs have demonstrated positive impacts on
tourism, where decommissioned structures are used for
recreational diving and fishing [21][22].
As a high-level means of assessing natural and societal
advantages and disadvantages of tidal lagoons and wave
energy devices, impacts on ecosystem services and associated
societal benefits were considered. Ecosystem services are
‘outputs of ecosystem processes that provide benefits to
humans (e.g. food, water)’ [23]. They are linked to ecosystem
functions, which are the biological underpinning of ecosystem
services (e.g. productivity). The ecosystem services
framework applied here was developed for the marine
environment (Fig. 1) [13][24]. Possible effects of tidal lagoons
and WECs on marine ecosystem services were assessed
(Tab.1); this ought to be viewed with caution given the current
absence of firm evidence for such devices. Assessments were
based on evidence from other infrastructure projects or expert
judgement, and effects would depend on site-specific factors.
Societal benefits, and in particular those linked to aesthetic
benefits and seascapes, are difficult to consider; these services
were merely included to demonstrate the link between the
natural environment and societal benefits. The perception of
desirability or undesirability of effects of artificial structures
in the marine environment is a value judgement related to
societal goals and expectations [25]. Linked to such
judgement, the following management targets were identified
[26]: Provision of suitable habitat to promote living resources
for exploitation of food (such as shellfish and fish), living
resources that are the focus for recreational or educational
activities (angling, snorkelling, rock-pooling, bird-watching),
conservation of endangered or rare species and rocky substrate
assemblages (biodiversity) for conservation or mitigation
purposes.
The focus of this study was the provision of new habitat by
tidal lagoons and WECs, with the aspiration to create designs
and measures that enhance biodiversity.
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TABLE I
POTENTIAL EFFECTS OF WAVE ENERGY DEVICES AND TIDAL LAGOON INFRA STRUCTURE ON PROVISION OF ECOSYSTEM SERVICES (ADAPTED
FROM SMYTH ET AL. 2015 [13])
Ecosystem services
Wave
device
Tidal
lagoon
Comments
Intermediate ecosystem services
Primary production
+
+
More hard substratum, more primary production depending on photic
zone
Larval and gamet supply
?
+/?
Changes dependent on local hydrographic regime
Nutrient cycling
0/?
-/?
Changes in the retention and dispersal of nutrients; this may be only
relevant for tidal lagoons.
Formation of species habitat
++
++
More environmental heterogeneity
Physical barriers
0
-
Physical barriers will impact colonising species
Biological control
-
-
Hard substratum may provide habitat for invasive/alien species and
alter the food web
Waste breakdown
0
+
Colonising species may contribute
Carbon sequestration
+
+
Increased C-sequestration and biomass (C-storage) associated with
artificial reefs/ hard structures.
Final ecosystem services
Fish and shellfish
+
++
Benefits of both hard substratum and floating structures
Algae and seaweed
++
+
Hard substratum and floating structures allow seaweed/algal growth,
depending on photic depth (Case study 2).
Ornamental materials
0
+
Increased habitat complexity and biodiversity associated with
structures
Genetic resources
?
?
Current gap in knowledge; depending on habitat formation
Water supply
0
0
Negligible in locations suitable for wave and tidal energy devices.
Climate regulation
0/+
0/+
More C-sequestration and storage associated with hard substratum;
difficult to be detected.
Natural hazards protection
+
++
Wave devices dissipate wave energy, tidal lagoons can protect against
flooding, erosion, wave exposure.
Clean water and sediments
+/?
+/?
possibly indirectly through promotion of filterfeeders and kelp/algae
Places and seascapes
0
+/-
These will be changed by tidal lagoons; subject open to subjective
perception.
Goods and benefits
Food (wild, farmed)
+
+
Some fishing and aquaculture may be possible through increased
infrastructure
Fish feed (wild, farmed, bait)
+
+
Increased biodiversity and biomass associated with structures
Fertiliser and biofuels
0/+
0/+
Hard substratum allows seaweed/algae growth depending on photic
depth; unlikely to be commercially viable in near future.
Ornaments and aquaria
0/+
0/+
Increased biodiversity associated with structures
Medicines and blue
biotechnology
?
?
Current gap in knowledge, but potential.
Healthy climate
0/+
0/+
Increased C-sequestration and storage on hard substratum, but
difficult to quantify.
Prevention of coastal erosion
+
+
Structures that dissipate energy have may prevent erosion.
Sea defence
+
++
Structures and colonising organisms can provide sea defences.
Waste burial/
removal/neutralisation
0
0
Possible use of waste for moorings, but no great potential anticipated.
Tourism and nature watching
+
++
Tidal lagoon in particular has great potential for increased access to
sea (e.g. angling, birdwatching, sports)
Spiritual/cultural well-being
0/?
0/?
Changes may be positive or negative
Aesthetic benefits
0/?
0/?
Changes may be positive or negative
Education, research
+
++
Research opportunities exist for both sectors; the accessibility of tidal
lagoons allows wider educational opportunities.
Health benefits
0/?
0/?
Changes may be positive or negative
Key: ++ potential strong positive effect; + potential positive effect; 0 negligible effect; - potential negative effect;
? significant knowledge gaps in evidence
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Fig.2 Conceptual model illustrating opportunities to transform wave and tidal
energy devices into artificial reefs. Images: top left, biogenic reef formed by
Sabellaria alveolata; top right, altered construction material through rock
pools drilled into coastal defence structure (photo Louise Firth); bottom left,
sheltered conditions utilised by BioHaven floating islands (Frog
Environmental Ltd.); bottom right, added habitat features through rock-rolls
(Salix Ltd.).
III. BIODIVERSITY ENHANCEMENT
Generally, methods and advice regarding ecological
enhancement during the planning, design and construction
stages of hard coastal structures are still experimental,
although some have been included in constructions as
mitigation [27]. Publications describe methods of general and
specific ecological enhancement. General ecological
enhancement includes practises such as arranging rocks in
groynes to maximise void space for fish and invertebrates to
utilise [16]. Specific ecological enhancement is used for
targeting particular species or habitat niches, such as building
rockpools in vertical walls [28].
In this paper we presume that enhancement of biodiversity
is a desirable ecosystem service. However, this does not need
to be the case. Particularly in the vicinity of underwater
turbines it may be advantageous or necessary to keep the area
as biota-free as possible to ensure the efficient functioning of
a turbine and to avoid striking passing animal [29][30][31]. It
is accepted that these properties may have priority. However,
tidal lagoons and WECs are complex and potentially
expansive structures, and enhanced biodiversity of many
features of the infrastructure would not compromise their
functionality as power stations.
Suggested concepts were to a large extent based on the
latest research on eco-engineering of coastal defence
structures in the coastal and marine environment, but we also
consider engineering solutions developed in freshwater
systems, aquaculture and in restoration ecology. We suggest
four broad areas that can be pursued to environmentally
enhance wave and tidal energy devices (Fig. 2): a) existing
features and materials may be altered to improve settlement
conditions, such as changes in the roughness of surfaces or the
creation of niches and shelter; b) reef-type habitat may be
added, such as rocks of different size, shape and erodibility; c)
marine energy devices generally alter some environmental
properties and often create shelter in or around the
infrastructure, which offers further potential for biodiversity
and allows the establishment or expansion from other areas of
new local features; d) hard substratum such as rock armour
provides attachment surfaces for species that themselves
create biogenic reefs, for example oysters, mussels or tube-
building worms (e.g. the Sabellaria honeycomb worm), which
accelerate a reef-building process. Biogenic reefs are “Solid,
massive structures which are created by accumulations of
organisms, usually rising from the seabed, or at least clearly
forming a substantial, discrete community or habitat which is
very different from the surrounding seabed. The structure of
the reef may be composed almost entirely of the reef building
organism and its tubes or shells, or it may to some degree be
composed of sediments, stones and shells bound together by
the organisms,” [32].
In this paper we outline potential biodiversity promoting
design solutions which can be included in the planning and
construction phase of wave or tidal range energy devices to
attract large numbers of species and to reduce the impact on
the surrounding environment.
Spatial heterogeneity can enhance the resistance of
ecosystem functions by facilitating the persistence of
individual species through providing a range of resources and
microclimate refugia [23]. It may further increase overall
species richness and as a consequence functional redundancy
[33].
IV. ALTERING CONSTRUCTION MATERIAL
The design of artificial coastal structures has a major effect
on the natural environment [25]. The magnitude of the effect
appears to be heavily dependent on the nature of the created
structure, the location and the composition of the native flora
and fauna at the time the artificial structure is created [25].
Marine
Energy
Device
Altering
construction
material
Adding
habitat
features
Establishing
biogenic
reefs
Utilising sheltered
condition created
by energy device
rockpools
texture
Reef-rolls
overhangs
Shallow
slopes
Pre-cast
reef blocks
Erodible
materials
Different
sized rocks
Mussel
beds
Oyster
bank
Sabellaria
reef
Creation of
seagrass
meadow
Kelp forest
BioHaven
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The structural complexity of the building materials and the
architecture play an important role for the number, type and
diversity of animals and plants colonising the artificial
material. By mimicking a rocky shore with a mixture of rock
sizes, roughness and crevice sizes, artificial materials can
attract marine life [16]. Incorporating porous, calcite rich
materials can provide habitat for other organisms, especially
rock boring species. This can improve the habitat by
increasing the roughness of the materials via bioerosion,
which will then be exploited by other species. Also, materials
that have a variety of vertical and horizontal surfaces that
retain water at low tide will encourage intertidal species to
colonise [15]. The gradient of substrate can further affect
species composition. Most naturally occurring rocky shores
have a gentle slope in comparison to artificial structures like
sea walls. Generally vertical substrates support fewer mobile
marine organisms [34]. Surface characteristics such as texture,
complexity, size and even colour affect the number and types
of organisms that colonise artificial substrates [35].
An extension of the modification of surface textures is the
creation of rockpools which are excavated from rock armour.
Artificial pools of different depth were drilled into a coastal
defence breakwater in Wales (UK) to enhance biodiversity
[14]. It was found to be an effective and affordable measure of
habitat enhancement.
V. ADDING HABITAT FEATURES
An alternative to modifying coastal infrastructure directly is
the fitting, or retro-fitting, of habitat features. For example,
rather than excavating artificial rock pools directly these may
be attached to a seawall, which attracts sessile and motile
species, particularly in upper intertidal areas [36].
Another method to improve the structural complexity of an
artificial reef is the deployment of larger precast units. These
are designed to attract specific species or to offer multiple
habitat types. A recent example is the development of a
‘Bioblock’ [27] during a collaborative project between
SEACAMS Bangor, Conwy Council and Ruthin Precast
Concrete (RPC). The objective of the Bioblock is to provide
additional habitat types that can be incorporated into rock
armour, breakwaters, groins and revetments at the
construction stage. The Bioblock has rockpools, circular pits
and longitudinal depressions. ‘Reefballs’ are based on a
similar idea but are designed differently. Depending on the
artificial environment and the enhancement unit in question,
these can be deployed either during construction or
retrospectively to effectively increase local biodiversity [25]
[36].
In recent years engineering solutions have been explored
that prevent erosion of coastal habitats, and in particular the
loss of sand and mud. In the Netherlands gabion cages filled
with fished-up oyster shells were mounted on silt in intertidal
areas. A continuous artificial oyster shell reef was created,
200 metres long and ten metres wide. These shell bioreefs can
potentially be tailored to specific needs of an artificial
structure to maximise the environmental benefits [37].
It seems plausible that such artificial features could be
added to wave and tidal energy installations. They could, for
example be considered to contribute to moorings, integrated in
the armour of tidal lagoon walls or placed into adjacent areas
of the energy devices where they neither affect the function of
the device nor impact on other existing users of the space.
VI. UTILISING CHANGED ENVIRONMENTAL CONDITIONS
CREATED BY ENERGY DEVICE
Wave and tidal energy devices in the coastal and marine
environment will change hydrodynamic conditions either
directly or indirectly. Areas of the seafloor or the waterbody
may become more sheltered, which offers opportunities for
new features. Wave energy devices, for example, can create a
‘wave-shadow’ with much reduced wave activity at its leeside.
During the EU funded project MARIBE [38] it was
established that the wave energy sector could sit side-by side
with aquaculture facilities. The two business sectors form a
feasible multi-user space combination within the Blue
Economy for the Mediterranean as well as the Atlantic area.
For example, wave energy converter (WEC) overtopping
platforms, such as the Wave Dragon design, calm wave action,
and would therefore create environmental off-shore conditions
suitable for seaweed farming, such as long-line cultivation of
brown seaweed Saccharina latissima and other kelp species
(Case Study 2).
The proposed tidal lagoon areas in the UK will potentially
create environments of high shelter (low wave action) and
contain sandy and muddy substrate, conditions appropriate for
seagrass. Water clarity may become higher within the lagoon
due to the reduced influence from any rivers, reduced wave
action and generation hold periods when there is no flow and
light availability, which could become sufficient to support
seagrass growth. Generally, seagrass meadows are declining
at an unprecedented rate [39] [40], therefore the ecosystem
services they provide are also at risk including their role in
fisheries production, biodiversity provision and nutrient
cycling [41]. In Europe and the UK, land reclamation, coastal
development, overfishing and pollution over the past centuries
have nearly eliminated seagrass meadows, with most countries
estimating losses of between 50-80% of the original area.
Tidal lagoons therefore have the potential to provide an
opportunity for biodiversity enhancement through the creation
of seagrass habitat.
VII. CREATING BIOGENIC REEFS
In engineering terms biogenic reefs are also referred to as
“soft” engineering solutions [42]. They include oyster and
mussel beds and tube-worm reefs. These features offer
protection from hydrodynamic impacts, retain sediment and
reduce erosion, but they also diversify the habitat.
The restoration of native oyster reefs is an international
aspiration for nature conservation [43]. This has proved to be
a challenging target and several studies describe the feasibility
and problems of the natural recovery of depleted oyster stocks
[44]. Challenges range from knowledge gaps in the ecology of
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oysters, e.g. the dispersal patterns of their larvae, to concerns
about biosecurity of introducing oysters from outside. The
area of the proposed tidal lagoon in Swansea Bay is a
potential area for oyster population restoration because of its
well documented former oyster stocks and fisheries, and the
company TLSB aspires to contribute to the recovery of oyster
reefs (Case Study 1). The aim is to create reefs undisturbed by
fishing impacts and to promote biodiversity. The efforts
would have knock-on benefits for the local oyster fishery by
increasing the overall supply of oyster larvae and spat in the
area.
Tidal energy lagoon walls offer opportunities for constructing
spatting ponds which stimulate the settlement of oysters [44]
[45]. Spat collectors inside the ponds encourage the
attachment of oyster larvae during the breeding season. The
method is used by the oyster industry in Cork Harbour, where
ponds are stocked with 700-800 oysters which produce up to
50 million spat oysters for on-growing [44].
The reef-forming honeycomb worm Sabellaria alveolata
and the related ross worm Sabellaria spinulosa are protected
feature under the EC Habitats Directive. Both species are
widespread around the European coast and are found on hard
substrata on exposed, open coasts with moderate to
considerable water movement where suspended sand is
available for tube building. Their distribution is therefore
likely to overlap with potential areas of tidal energy devices.
The main benefit of Sabellaria reefs is their function as
‘ecosystem engineers’: they provide a habitat for other species,
thereby supporting a wide variety of invertebrates. They
support a higher diversity of species than surrounding sandy
areas [46].
Sabellaria alveolata, the honeycomb worm, may benefit
from the presence of the tidal lagoon walls. The tube worm is
generally found in lower intertidal and shallow subtidal areas
with relatively strong water movement. Initially larvae of
S.alveolata settle on firm substratum such as rock, pebbles or
bivalve shells (Fig.3). They construct firm tubes by cementing
sand grains together, and the first step to a reef is generally a
veneer of tube aggregations covering the settlement substrate.
The firm worm-tubes then provide settlement substrate
themselves for future generations, creating a self-promoting,
sustainable system, which can result in substantial reefs.
Artificial coastal defence structures were found to provide
settlement substrate similar to natural materials and were
found to be colonised by large numbers of S.alveolata [25].
CASE STUDY 1. ECOSYSTEM ENHANCEMENT OPPORTUNITIES
FOR THE TIDAL LAGOON SWANSEA BAY
Fig.3 Top: Outline of the proposed Tidal Lagoon Swansea Bay. Bottom:
Opportunities for environmental enhancement through establishment of
ecological features (Seagrass, honeycomb tube worms, oyster and mussel
beds).
Tidal Lagoon Swansea Bay plc (TLSB) proposes to construct
a tidal energy lagoon in Wales (UK). The infrastructure will
be made up of a 9.5 km breakwater wall extending out from
the Port of Swansea, and it will enclose an 11.5 km² tidal area.
The nature of the project requires rocky building materials
which will be placed on top of existing inter and subtidal soft
substratum in Swansea Bay. The lagoon wall will add to the
natural rocky shore in Swansea Bay. Changes in the fauna of
the lagoon area are unavoidable since soft and rocky shores
are colonised by different species communities, albeit with
some overlap. It is accepted that the presence of the lagoon
will alter the nature of the invertebrate and fish community,
but it is deemed desirable to optimise the lagoon design so
that it functions as an artificial reef and creates opportunities
for the ecological renewal of an environment (Swansea Bay)
altered by centuries of heavy industry and over fishing.
The EU funded project SEACAMS explored opportunities
of using different materials, textures and structures which
could affect the number of species attracted to lagoon walls
and the biodiversity of marine life it supports [47]. The
following concepts are currently under consideration; the
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environmental enhancement strategy of TLSB is still under
development.
It was proposed that the surface of the rock armour should
be uneven and as porous as possible. A mixture of different
materials should be used as rock armour, or added to the rock
armour. Some of the material could be softer than others, thus
allowing different degrees of erosion. Whilst the quarrying
process will provide some etching of the rock, the surface of
the building materials could be further modified artificially.
Ridges, crevices and depressions could be deliberately
chiselled into the lagoon wall. Artificial rockpools could be
added to the rock armour of the lagoon in the intertidal area.
Precast reef blocks such as ‘Bioblocks’ or ‘Reefballs’ could
be integrated into the lagoon wall to maximise the diversity of
colonising species. Gabion-type cages and mattresses filled
with local bivalve shells or smaller rocks could be integrated
into the lagoon wall to attract benthic invertebrate fauna.
Sources of shells could include waste from shellfish
processors and restaurants. The slope of the foot of the lagoon
wall should be drawn out with a shallow gradient.
A program to create oyster reefs inside the lagoon could be
facilitated through the provision of ponds integrated into the
wall or separately inside the lagoon area. Current oyster stocks
are low and the remaining population in Swansea Bay consists
of relatively old individuals. Once the lagoon is built these
individuals could be used as broodstock. Larvae and spat
could be either hatched in spatting ponds inside the lagoon or
in laboratory facilities located on the lagoon wall. Juvenile
oysters which settled on cultch material will then be
transferred to areas inside the lagoon to grow on and
eventually create a reef. Larval production and settlement
success could then be monitored.
In addition to oysters, a program that promotes the
colonisation of the honeycomb worm (Sabellaria alveolata) is
also possible; the species is naturally colonising natural rocky
shores in the region as well as other infrastructure. Finally, the
sheltered nature of the lagoon creates significant potential for
the environment to become affable for seagrass, particularly
as the physical dynamics of the sediments settle post
construction and create less turbid waters. Initial experiments
to create seagrass habitat (Zostera spp.) have been established
in other locations within the Bristol Channel to test
appropriate methods for such habitat creation. The active
creation of primary producer habitat such as seagrass that
rapidly develops sedimentary carbon stores opens new
opportunities in terms of the development of markets in so
called ‘blue carbon’. Further opportunities to create multi-
species, integrated multi-trophic systems inside the lagoon
area could be considered, including mussel and seaweed
cultivation.
CASE STUDY 2. COMBINING WAVE ENERGY DEVICE WITH
OFFSHORE AQUACULTURE
Fig.4 Top: Wave Dragon energy converter. Bottom: Seaweed line culture.
The EU funded Horizon 2020 project MARIBE assessed the
feasibility of combining wave energy devices with offshore
aquaculture in one multi-user space [38]. Wave Dragon is a
private Danish/UK based company working towards the
commercialisation of a wave energy converter (WEC)
technology to extract electricity directly from ocean waves,
and Seaweed Energy Solutions (SES) is a Norway- based
seaweed innovation and business development company.
This concept envisages an array of wave energy converters
(WEC) of a design created by Wave Dragon, combined with a
seaweed farm. Wave Dragon has deployed a grid connected
237 tonnes pilot WEC plant in Nissum Bredning, Denmark.
The technology is a floating, slack-moored wave energy
converter of the overtopping type. SES has proven capacity to
cultivate brown seaweed (Saccharina latissima and other kelp
genus) on a large scale (long-lines), and it provides a platform
for the further development of cultivation technology. An
industrial scale hatchery was built and it successfully supplied
seeds for 100-150 tonnes wet weight biomass. A pilot farm in
Frøya is one of the largest seaweed cultivation farms to date in
Europe. The current products are distributed to a niche food
industry market. Wave Dragon is looking to develop its
technology further at commercial farm scale. SES is looking
to further improve its harvesting technologies, including
mechanisation, and to help increase harvest volumes.
Location of farms in Welsh offshore waters, calmed and
occasionally being submerged by a wave machine, will
increase the operational days and thus make kelp production
feasible in exposed waters. The processed seaweed can be
sold as a high value material for food and health products
(nutraceuticals), cosmetics, animal feed markets, among
others.
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The seaweed farm will benefit from calmer water behind
the devices, enabling it to be located in areas which would not
normally be viable. During periods of rough seas, electricity
from the WECs can be used to winch seaweed farms lower
into the water, protecting them from any ill‐effects. Electricity
from the WECs will be exported to the grid. Further, co-
locating two projects that are already in the licensing process
could benefit from the multiple use of space, and there are
also significant synergies for installation, inspection and
maintenance operations. The expected location of the pilot
deployment is off the Welsh coast.
VIII. CONCLUSIONS
This review of opportunities for wave and tidal energy
devices to become artificial reefs suggested that there are
several pathways for these structures to enhance biodiversity.
Construction materials can be modified, artificial reef-type
elements can be added, and changed environmental conditions
in the vicinity of wave and tidal energy devices could be
utilised. Lessons can be learned from existing research of
coastal defences, port infrastructure or offshore wind turbines
[48], and concepts for ecosystem enhancement developed for
other sectors could be adapted for the marine and coastal
environment. However, the evidence of ecosystem
enhancement measures is still limited and the challenge will
be for renewable energy organisations to work closely with
ecologists and trial proposed concepts in the natural
environment.
ACKNOWLEDGMENT
The MARIBE project has received funding from the
European Union’s Horizon β0β0 research and innovation
programme under grant agreement No. 652629. The
SEACAMS project research study was part-funded by the
European Regional Development Fund through the Welsh
Government.
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