Utilising novel methods to determine potential interactions between subsea power cables and benthic reef forming species limaria hians and modiolus modiolus

Abstract

The installation of oshore marine renewable energy devices is expanding rapidly as the world
moves to combat a warming planet by reducing the carbon footprint of energy generation.
A consequence of this is the installation of infrastructure into new areas leading to more interactions
between new benthic communities and infrastructure such as subsea power cables.
Developers are now required to have a net biodiversity gain on the environment and as such,
require a better understanding of how infrastructure impacts habitats and species conservation
interests. Two such species are the biogenic reef building bivalves Limaria hians and Modiolus
modiolus, Priority Marine Feature (PMF) species in Scotland. Both species build expansive
reefs across the seabed meaning subsea power cables making landfall are inherently likely to
encounter these reefs causing presently unknown impacts. Using a variety of methods and technologies,
the potential of cable routing encounters with both of these species, remote sensing of
L. hians reef habitat and the physical impact of cable presence on M. modiolus were assessed.
Habitat suitability models for each species were developed to predict the amount of habitat
considered suitable for each species and this was compared with potential interactions with
the subsea cabling infrastructure in Scotland. Much of the suitable habitat for each species
runs parallel to the coast increasing the likelihood of intersecting with developments, especially
as cables make landfall or transit narrower bodies of water between land such as island interconnectors.
With remote sensing, it was not possible to visually identify an acoustic signature
of L. hians with the methods employed in this study, like has been shown to be possible with M.
modiolus. However, signicant statistical variation was observed within bathymetry derivatives
between areas of conrmed presence vs absence. Additionally, it was demonstrated that despite
L. hians cryptic appearance, it was possible to use broad classication of images to map large
areas of reef habitat when used in combination with high resolution ground truthing ROV
video. The physical impacts of cable presence of M. modiolus were shown to have an impact on reef presence in the very near proximity to an installed cables with an undetermined secondary
eect at moderate distance. Overall, the footprint of the impact was small in comparison to
the whole reef scale, but further observation of this case study could reveal the extent to which
recolonisation by this long-lived species takes place close to the cable.
Research undertaken for this thesis has shown that subsea power cables are likely to interact
with L. hians and M. modiolus reefs but going forward but there are several methods and
technologies which can assist in mitigation of potential negative impacts. Improving knowledge
of where these reef habitats are found can help lower the impacting footprint of subsea cable
installation at the project design phase through careful routing and design with the added
advantage of minimising inadvertent licencing issue which may arise during construction if
such benthic PMF features are unexpectedly encountered. However, because of their long-lived
nature and slow potential for expansion, further long-term research is required into the capacity
of these reef to recover from disturbance from renewables infrastructure.
This thesis' data chapter structure should be read in order to assess the 'where', 'how' and
'what' of industry interactions with these case species. 'Where' are they located (chapter 2),
'how' to we identify them (chapter 3) and 'what' are the impacts of industry to them (chapter
4).

Date of Award	11 Nov 2024
Original language	English
Awarding Institution	University of the Highlands and Islands
Sponsors	Interreg VA - Cross Border
Supervisor	Clive Fox (Supervisor) & John Howe (Supervisor)