A review of benthic ecological surveying for marine renewable developments in Scottish waters

4 Considerations for planning survey strategies and campaigns

4.1 Existing guidance for benthic survey activity

4.1.1 Background

Benthic sampling regimes (sampling and survey design principles) adopted by MRE developers are commonly determined on a site-by-site basis through discussion between the MRED developer, survey contractors, and advisory bodies, and therefore vary both regionally and internationally. However, to help standardise the process there have been several key guidance documents produced or adopted by the MRE sectors in different parts of the UK.

The seabed surveying recommendations produced by NatureScot (Saunders et al., 2011) are relevant for the Scottish renewables industry, but were not formally published. However, these mainly focus on the wave and tidal sectors, which were considered the most pressing development pressure at that time. With offshore wind now much more to the fore, and with the learning achieved since 2010, these recommendations are regarded as out of date and need to be refreshed.

There have also been seabed survey guidance documents produced for English and Welsh waters as well as internationally, which provide recommendations for surveying benthic ecology traits within MRED areas as well as for other sectoral interests and research (see Boyd, 2002; Ware & Kenny, 2011; Reach et al., 2013a; Oil and Gas UK, 2019). Existing seabed survey guidance documents relevant to MREDs for England and Wales are summarised below as well as other national guidance.

4.1.2 Regional guidance - Wales

Natural Resources Wales (NRW) developed a suite of guidance on methods and approaches for survey and monitoring of benthic marine habitats in 2019 which undergo regular review and updates (latest update was 2021). Its aim is to assist developers in designing and planning benthic marine habitat surveys and monitoring, where this is required for EIA in support of proposed developments and activities in or near Welsh waters. The guidance (Natural Resources Wales, 2023) is split into nine separate documents with an overarching document setting out the main principles and methods which links with a series of guidance notes specific to key benthic habitats. It is based on an extensive review of marine conservation legislation, peer reviewed and grey literature, and provides very detailed recommendations in relation to designing, conducting, and reporting on benthic assessment surveys in general and for included habitats. It draws heavily and builds upon the recommendations of Noble-James et al. (2018) (described in section 4.1.4) in relation to sampling design and statistical analysis.

4.1.3 Regional guidance - England

Natural England (NE) produced a series of documents providing best practice advice on the use of data and evidence to support offshore wind farm development in English waters (Natural England, 2021a, 2021b, 2022a, 2022b). The advice ranges from baseline characterisation surveys and pre-application engagement, through to expectations at application and post-consent monitoring. Whilst they cover all receptors there are chapters focussed specifically on benthic habitats. As with the NRW guidance, it draws heavily on the recommendations of Noble-James et al. (2018).

4.1.4 National guidance – Offshore UK

Noble-James et al. (2018) provide JNCC’s best practice guidance for monitoring marine habitats, with a focus on sampling design. Although largely focussed on benthic monitoring of Marine Protected Areas (MPAs), it is applicable to the design of benthic surveys related to MREDs. It sets out a comprehensive framework for survey design and statistical analysis which is widely cited by regulatory authorities and MREDs and forms the basis of much of the key NRW and NE guidance.

In 2019 Oil and Gas UK (OGUK) produced guidance which provided an overview of the different categories and types of seabed surveys. The guidance outlined the recommended good practice for considering when to undertake a survey and designing seabed surveys for use within EIAs by the offshore Oil and Gas (O&G) industry on the United Kingdom Continental Shelf (UKCS) (Oil and Gas UK, 2019). This guidance is used extensively by those commissioning O&G operators, survey contractors, the regulator Offshore Petroleum Regulator for Environment and Decommissioning (OPRED) and SNCBs as a set of industry wide standards. Whilst they are specific to the O&G sector, many of the approaches and methods are relevant to MREDs and have been developed and refined based on the lessons learned from decades of benthic monitoring.

4.1.5 Other guidance – Offshore UK

There is a wider series of best practice, guidance, and review documents that, in the context of MRED benthic studies, have largely been superseded by the those summarised in previous sections. Some however remain at least partially relevant and are frequently referred to by the MRE industry (e.g., Davies et al., 2001; Boyd, 2002; JNCC, 2004a, 2004b, 2004c, 2004d; Curtis & Coggan, 2006a, 2006b; Coggan & Birchenough, 2007; White et al., 2007; Ware & Kenny, 2011; Judd, 2012; Piel et al., 2012; Henriques et al., 2013; Marine Management Organisation, 2014; K. Cooper & Mason, 2014; Cooper & Barry, 2017 and POSEIDON, n.d.). Therefore, consideration is required particularly when following historical scopes of work to ensure that sampling approaches follow appropriate guidance that is based on the most recent available literature.

4.2 Considerations for Scotland-specific survey and sampling regimes

The collection of robust baseline information is key for comparing the pre- and post-construction condition and patterns of change within benthic communities at MRED sites (Methratta, 2021). In addition, it is important that data from different surveys can be easily collated and compared for wider research on the potential large scale or cumulative impacts of MREDs. Scottish MREDs (particularly the wind sector) currently adopt benthic sampling regimes that draw upon appropriate guidance from various sectors (e.g., Saunders et al. 2011; Noble-James et al., 2018; Natural Resources Wales 2019a, 2019b; Oil and Gas UK, 2019; Natural England 2021a, 2021b, 2022a, 2022b; Parker et al., 2022), and utilise historical data entered into regional and international data portals such as:

• European Marine Observation and Data Network (EMODnet) Broad-scale Seabed Habitat Map for Europe (European Commission, 2024)

(EUSeaMap 2021 Broad-Scale Predictive Habitat Map for Europe (ices.dk))

• OneBenthic Portal.
• Marine Recorder (JNCC, 2022).
• UK Atlas of Marine Renewable Energy Resources meso-scale model (ABPmer, 2008).

Additionally, there are several key Scotland-specific data portals, datasets, and reports that are consulted to inform the benthic sampling and survey design process, which include:

• Marine Scotland Maps National Marine Plan Interactive (NMPi),
• NatureScot – Open data hub
• Crown Estate Scotland (CES)
• Geodatabase of Marine Features adjacent to Scotland (GeMS)
• The NBN Atlas
• Feature Activity Sensitivity Tool (FeAST)
• Descriptions of Scottish PMFs (Tyler-Walters et al., 2016).
• Scotland’s Marine Assessment 2020 (Moffat et al., 2020).
• The benthic environment of the North and West of Scotland and the Northern and Western Isles: sources of information and overview (Wilding et al., 2005).
• Sectoral Marine Plan: Regional Local Guidance Offshore Wind Energy in Scottish Waters: Regional Locational Guidance (Scottish Government, 2021).

Historically, Scotland’s marine area is largely under-sampled. Therefore, dedicated benthic surveys are often required to inform the characterisation stage of MRE development, particularly within offshore regions where there is a lack of survey effort. These surveys aim to provide suitable coverage of the area, whilst considering any historical data gaps (e.g., Xodus, 2023). Targeting and identifying the presence and distribution of cryptic benthic habitats and species (e.g., flame shell beds, Arctica islandica) throughout a site can be difficult when using traditional sampling techniques alone (e.g., geophysical, grab, drop-down video and still imagery). The utilisation of predictive approaches such as SDM and HSM during the sampling design process may be of benefit (e.g., A. islandica (Reiss et al., 2011), horse mussel beds, flame shell beds (Millar et al., 2019)) if historical data is available. Alternate sampling regimes that can detect the presence of benthic species such as eDNA (e.g., Wort et al., 2022) may be required.

Sampling regimes should occur within suitable buffered areas that can account for site-specific indirect impacts such as sediment suspension resettlement, and the potential introduction of Invasive Non-Native Species (INNS). Where the monitoring of recovery and loss to intertidal or subtidal species and habitat is required post-construction, it is expected that sampling regimes will include grab sampling and seabed photography in both disturbed and undisturbed areas, using methods compatible with those used in the benthic characterisation survey. Benthic sampling regimes should also consider the life-history stages of PMFs associated with benthic habitats, such as the eggs of flapper skate which are laid on cobble/boulder habitat in 20 – 50 m but may lay in shallower or deeper water (Thorburn et al., 2022) and have long gestation periods (Benjamins et al., 2021). There are habitat-specific guidance resources available with regional and site-specific context for defining and assessing a variety of biogenic reef structures recorded in proposed development areas, these are discussed in Section 4.4.

Benthic surveys of MREDs in Scottish waters utilise seabed imagery as a multi-faceted approach: to ground-truth acoustic data prior to grab sampling, delineate boundaries between habitats and biotopes, and inform on the presence and distribution of protected features throughout the surveyed area. Two main methods are used, point samples (multiple images from within a buffer of a target location), and transects (images taken at intervals along a set line). Point samples are used to ground-truth potential sediments prior to grab sampling to ensure the area is clear of obstruction, and that visible protected features are absent prior to grab sampling. Transects are used pre-construction to delineate features of interest and/or potential boundaries between sediment types interpreted from acoustic data sources. Post-construction transects can be used to target specific areas of an MRED to inform the seabed condition and infrastructure (biofouling) prior to activities that could impact the benthos such as cable replacements.

Grab sampling provides vital background information on the composition and quality of benthic sediments and associated fauna. Data is assessed against background standards of acceptable heavy metal and chemical concentration levels (Oslo and Paris Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR)) (Larsen & Hjermann, 2022); UK Offshore Operators Association (UKOOA) (Sheahan et al., 2001), upholding Scotland’s commitments under various regional, national, and international policies and legislations. It is used to inform on the condition of sediments pre- and post-construction, which has particular importance where energy industries have amalgamated or evolved (i.e., decommissioning of O&G and replacement with MRE, e.g., Beatrice Offshore Wind Farm (OWF)). Sampling for hydrocarbons, chemicals, and heavy metal provides data on the persistence of historical loading and potential resuspension of contaminated sediments during construction and decommissioning. Grab sampling for macrobenthic analysis can be used to inform sediment biotopes of high importance, which may require repeat sampling during post-construction surveys to monitor the recovery or loss of such features identified during pre-construction.

4.2.1 Examples of MRED survey strategies in Scotland

There have been many intertidal and seabed ecology surveys already completed for MREDs around Scotland. These have had to take into account the local issues, needs and constraints outlined in the previous section. The surveys have been associated with the established Solway, North Sea and Moray Firth offshore wind farms, the EMEC tidal and wave test centre sites in Orkney and a number of other tidal and wave technology deployment and development sites around the country. More recently ScotWind and INTOG seabed leasing rounds have also led to burgeoning survey activity. Examples of the surveying strategies adopted for some of these developments are listed in Table 4.1.

4.3 Spatial approaches to planning benthic surveys and sampling

4.3.1 Survey designs to detect change

The Before-After-Control-Impact (BACI) approach and the Before-After-Gradient (BAG) approach are two methodological sampling approaches used in marine surveys. BACI is a survey design that can be used to examine the effects of anthropogenic activities in the context of natural changes. This involves monitoring both impact and reference/control sites before (pre-construction) and after (post-construction) an expected impact has occurred. Control or reference sites are chosen in similar yet unaffected areas with a view to attribute changes at the impact site to the activity in question rather than natural variation or other potential factors. Parker et al. (2022) and Noble-James et al. (2018) provide guidance on selecting suitable control sites, reducing sample-induced variability, and improving robustness in the BACI approach.

The BAG approach (Ellis & Schneider, 1997; Methratta, 2021) involves sampling along a gradient with increasing distance from infrastructure (e.g., turbines) and includes sampling both inside and outside the MRED boundary before and after impact has occurred. BAG promotes the detection of effects over a spatial scale (distance independent variable) and does not require control sites.

Sampling design approaches should be established at the earliest possible stage, whilst considering the location of proposed infrastructure to ensure samples do not overlap inaccessible areas post-construction (Parker et al., 2022). No standard approach has been adopted in Scottish waters thus far.

Methratta, (2021) proposes a combined approach, owing to empirical evidence that impact gradients towards fisheries resources occur at wind farms, whereby larger effects close to turbine foundations attenuate with increasing distance. Therefore, combining BACI with distance-based methods can promote a powerful approach enabling characterisation of both the spatial and temporal variance associated with wind farms. Several enhanced BACI and BAG approaches include Distance-Stratified BACI (DS BACI), Distance-Stratified Control Impact (DsCI) and After-Gradient (AG). An appraisal of the benefits and limitations of these approaches for surveying fish communities can be found in Methratta (2020). A summary of the pros and cons of these approaches in the context of benthic monitoring are summarised in Table 4.2. Such methods should be accompanied by appropriate statistical models to account for pseudoreplication, for example.

4.3.2 Distance-based sampling approaches

Distance-based sampling approaches are commonly applied by the Oil and Gas and aggregates industries to sample sediments from the point source of an impact or potential contaminant (e.g., a well head). Several distance-based sampling approaches have been used to identify spatial patterns in benthic invertebrates arising from the physical presence of turbine foundations (e.g., benthic community and sediment enrichment (Coates et al., 2014; Braeckman & Moens, 2018; Lefaible, Colson, Braeckman & Moens 2019; Lu et al., 2019; HDR, 2019, 2020; Braeckman et al., 2020). Distance based sampling approaches have also been used to identify spatial patterns in fish and macroinvertebrates at offshore wind farm developments (Griffin et al., 2016). The results of the studies showed that in general, sediment grain size increases with increased distance from turbine structures whilst conversely abundance, density, richness of benthic species, and organic content decrease. Changes in sediment characteristics and community composition along spatial gradients are therefore attributed to sediment enrichment close to the subsurface infrastructure (Coates 2014; De Mesel et al, 2015).

There is no uniform incremental distance or design currently applied in benthic sampling approaches, however, sampling distances from turbines typically range from 90 – 200 m with controls placed 500 – 4000 m away. Comparison studies between BAG and BACI designs highlight the importance of sampling at an appropriate spatial scale. In the case of marine energy structures there may be an emphasis upon sampling station placement within 100 m of subsea structures due to the limited extent of any disturbance.

A meta-analysis conducted on several major offshore wind farm monitoring programs in the North Sea identified distance to structure as one of the key diversity indicators of long-term changes in soft-sediment communities (Coolen et al., 2022). Coolen et al. (2022) collated data from a variety of sources with distance ranging 1 m to 9761 m from nearest structures and identified that in using meta-analysis it was possible to detect long-term small changes, that are not detected in small, localised surveys. However, they advise on producing a set of standardised parameters to enhance generalization of effects and exchange of knowledge. The results also showed that the sampling requirements dictated the required scale, with fewer BRUV stations required in comparison to benthic characterisation stations (camera and grabs) (Methratta 2021).

4.3.3 Other spatial factors when choosing sampling approaches

There are numerous factors that require consideration when selecting the appropriate sampling approach. These are summarised in Table 4.3.

4.4 Considerations for targeting features of conservation importance

Benthic surveys are often conducted to identify and monitor the occurrence (presence/absence) and spatial extent of benthic receptors relevant to an MRE development and associated activities. Features of conservation interest are of particular relevance for such surveys and therefore the sampling design will normally reflect any known or expected features, such as Annex I habitats, OSPAR threatened and/or declining habitats and PMFs.

4.4.1 Annex I Features

Annex I habitats refers to the list of habitats afforded protection under the European Union (EU) Habitats Directive (transposed since EU Exit into UK law) within Special Areas of Conservation (SACs). Examples of Annex I habitats are provided below.

Reefs – these are rocky marine habitats or biological concretions that rise from the seabed. This feature therefore includes bedrock and stony reefs (Irving, 2009; Golding, Albrecht & Mcbreen, 2020) as well as biogenic reefs. Biogenic reefs include those habitats formed by the ross worm (Sabellaria spinulosa), the horse mussel Modiolus modiolus, the blue mussel Mytilus sp. and the organ-pipe worm (Serpula vermicularis) for example. The ross worm (Gubbay, 2007; Jenkins et al., 2018; Natural Resource Wales, 2019a) has a smaller distribution around Scotland compared to England and Wales, however Scottish records are predicted to increase as survey effort associated with the development of the offshore energy sector increases (Pearce & Kimber, 2020). Horse mussels (Modiolus modiolus) (OSPAR Commission, 2009a; Morris, 2015; Natural Resource Wales, 2019b) are long lived biogenic structures which occur in sea lochs and off Noss Head on the north east coast of Scotland. Blue mussel (Mytilus sp.), and the organ-pipe worm (S. vermicularis) (Moore et al., 2006) also occur in Scottish waters.

Other Annex I habitats include sandbanks slightly covered by water all the time (JNCC, 2019; Pinder, 2020; Natural Resources Wales, 2021c), mudflats and sandflats (Elliott et al., 1998; Curtis, 2015), estuaries, coastal lagoons, and large shallow inlets and bays.

4.4.2 Priority Marine Features

PMFs relate specifically to 81 species and habitats identified as a conservation priority throughout Scotland’s sea area. All PMFs receive a degree of protection whether within or outside the MPA network through the National Marine Plan general policies which state ‘development and use of the marine environment must not result in significant impact on the national status of Priority Marine Features’ (Scottish Government, 2015).

A review of the PMF list was conducted by NatureScot in 2020 identifying eleven PMFs within 6 NM considered most vulnerable to the impacts associated with bottom-contact towed fishing and required additional protective measures that extended beyond the MPA network. The eleven PMFs were blue mussels, cold water coral reefs, fan mussel aggregations, flame shell beds, horse mussel beds, maerl beds, maerl or coarse shell gravel with burrowing sea cucumbers, native oysters, northern sea fan and sponge communities, seagrass beds and serpulid aggregations. Information sheets have been produced for each feature and can be found on the Marine Directorate website on PMFs.

Based on the location of current lease sites, it is possible that MRED boundaries will both intersect and be within the vicinity of the MPA network, Annex I habitats, and PMFs. Therefore, consideration of such features and knowledge of their distribution and quality is required pre-construction to inform the sampling approach, post-construction monitoring (where appropriate) and decommissioning.

A series of documents, listed below (see Table 4.4 and Table 4.5), are available which provide guidance on appropriate assessment techniques for benthic features of conservation interest. Some are specific to Scotland, whilst others are applicable UK-wide and have been to some extent used by the wind MRE sector. A key step will be applying these assessment techniques to species and habitats identified across Scotland’s wind, wave and tidal MRE sectors. However, for many target conservation features (species and habitats) within Scottish waters there remains no standardised guidance for surveying and assessing their abundance, distribution, and quality.

4.4.3 Fish surveys

Fish spawning habitat assessments

Fisheries surveys are usually treated as a separate assessment entity, however, there are certain conditions where benthic surveys may be required to help understand the possible importance of habitats for commercially important fish species such as sandeels (Ellis et al., 2012). Fish spawning habitat assessments indicate whether the seabed consists of ecologically important habitat spawning/nursery grounds for fish species such as herring (Reach et al., 2013b).

Sandeel population surveys

Guidance for conducting sandeel assessments for Scottish MREDs is provided within Latto et al. (2013). The Beatrice OWF post-construction sandeel survey technical report (BOWL, 2021) provides an example of a sandeel survey and follows methodologies designed in consultation with the MD and MD Licensing Operations Team (MD-LOT).

Essential fish habitats

Essential Fish Habitats (EFH) are identified as waters and substrate around Scotland necessary for the spawning, breeding, feeding, growth, and maturity of fish and shellfish species. A series of spatial outputs from Franco et al. (2022) have been published for 29 species (20 fish including three elasmobranchs and nine shellfish) and can be used as an evidence base to inform future planning and project level assessments.

4.5 Overview of other factors for consideration for MRED benthic surveying

There are numerous factors to consider throughout the lifespan of an MRED which could influence the methods of benthic surveying that are chosen. These can be broadly categorised into scoping, location, and operating factors. Scoping factors relates to the MRE sector in question (i.e., wind, wave, tidal), and the primary aim of the project, whether that be for research and development purposes (i.e., test/demonstration sites) or full-scale commercial deployment, and the stage of the MRED. Location factors considers geographical, site-specific factors relating to the environmental, biological, and physical condition of the site and the availability of suitable baseline data. Operating factors consider the feasibility (practicalities and cost) and jurisdictional limitations associated with the type of benthic survey.

4.5.1 Consideration of scoping factors

The choice of surveying method will depend on the stage and type of development (See Table 4.6). The benthic survey protocols adopted for test, demonstration, and pre-commercial stages of wave and tidal developments have historically differed from those adopted for commercial scale wind developments. In addition, to date in Scottish waters, the benthic survey requirements for wave, tidal and wind sectors have largely been selected and implemented on a case-by-case basis, however a more systemic sector-wide approach for each and possibly all marine energy sectors may be of benefit.

The identification of suitable benthic sampling techniques is required at each key development stage to ensure sampling effort is maximised to the benefit of both the environment and the MRE industry. The collation of historically relevant data is vital during the benthic characterisation stage to identify data gaps and therefore where survey effort should be maximised. In England and Wales, data repositories such as OneBenthic and Regional Seabed Monitoring Programme (RSMP) are utilised whilst in Scotland historical seabed data can be obtained from a combination of OneBenthic, Marine Recorder (biotopes/species), the NMPi (PMFs/protected features) and EMODnet data portal (Vasquez et al., 2021).

4.5.2 Considerations for a strategic surveying approach

Benthic sampling is most commonly conducted on a site-by-site basis, which provides some evidence on species and habitat distribution and abundance. However, benthic communities can often be disparate and patchy over quite short distances. This can lead to difficulties producing reliable and replicable results from small sample numbers and can also make the use of wider-scale habitat/community models less applicable.

Strategic sampling at a local level aims to minimise time and monetary effort in acquiring new sample data. Such sampling regimes rely on the availability of suitable existing data in order to identify gaps in a survey area that would benefit from additional data collection.

Strategic sampling at a region-wide level is conducted using sampling approaches such as the RSMP. The RSMP is a big data approach to macrofaunal baseline assessment and monitoring of the seabed (Cooper & Barry, 2017). The dataset comprises over 33,000 macrofauna samples with 83% containing associated sediment PSD data, from a combination of historical and targeted sample data collected during dedicated regional surveys, to fill gaps in spatial coverage within each region.

Strategic sampling strategies like RSMP promotes the use of data that already exists within a lease area. Surveys can then fill spatial data gaps whilst targeting habitats or species which may pose the greatest environmental consenting risk, or where more information is required to fully assess the potential impacts of the developments.

The POSEIDON (Planning Offshore Wind Strategic Environmental Impact Decisions) project facilitates regional-scale strategic sampling approaches. The POSEIDON project is adopted throughout England and Wales to collect environmental baseline data and produce updated spatial models for key species (receptors), assemblages, and a suite of ecological metrics (diversity, functional traits). These models will be used to identify regions that are most vulnerable to potential offshore wind impacts. Mapping environmental risk using this approach will help guide future offshore wind development rounds and wider marine planning by demonstrating regional scale changes in biodiversity (including positive and negative change). The POSEIDON project has built upon previous benthic sampling protocols (e.g., that of Ware & Kenny (2011) and the RSMP) and provides a protocol for sample collection (including grab and eDNA samples) and processing likely to be applicable throughout Scotland. Adopting a regional-scale sampling approach in Scottish waters would be of benefit across marine sectors and a single unified method of collecting and displaying benthic data would synergise data collection effort throughout the UK (Cooper, Mason & Lozach, 2021).

4.5.3 Considerations of cross boundary issues

MRED programmes can span local and regional boundaries as well as national boundaries. Consideration should be given to any potential boundaries encompassed within MRED areas to ensure that the benthic survey techniques adopted are systemic and effective across jurisdictional boundaries. Strategic sampling approaches such as those adopted in England (Cooper et al., 2021) promote regional-scale sampling over project-specific sampling plans resulting in effective and appropriate temporal data collection. If a regional-scale strategic benthic sampling approach was adopted for Scotland, a suitable division of regions is required to ensure sampling is locally relevant. The Scottish marine area is divided into eleven regions for regional marine planning purposes (The Scottish Marine Regions Order, 2015). These divisions are largely based on physical characteristics and therefore could be suitable boundaries for regional-scale benthic sampling approaches. However, some sampling techniques may only be appropriate at a local scale rather than regional-scale due to the spatial resolution of the acquired data and the time/monetary constraints associated with up-scaling a survey area (e.g., AUV surveys).

4.5.4 Utilising existing data for survey planning

The type of benthic data required at each development stage is largely determined by the quality of historically available data. Typically, the greatest scale of data collection is conducted at the pre-production stage to fully characterise the seabed.

The broad-scale habitat type coupled with further geophysical (depth), morphological (features) and biological (flora/fauna) considerations largely determine the methods of benthic sampling and analyses that are most appropriate. The EU SeaMap predictive BSH habitat map (Vasquez et al., 2021) is an effective precursory tool used for visualising potential seabed habitats during data collation exercises and for selecting target sample locations across representative substrates during the characterisation stage.

4.5.5 Considering the potential impacts arising from surveying activity itself

Benthic survey activities may produce a footprint that require mitigation to reduce impact to sensitive habitats and species. Some methods such as trawling lead to mortality of the sampled fauna and leave damaged organisms behind. Features that may be impacted by benthic surveys are summarised in

Table 4.7. Fragile seabed habitats, rare/protected seabed habitats and species such as sponges and corals, biogenic reefs, burrowed mud and sea pen habitats can be directly impacted by the benthic survey methods chosen, whilst those categorised by physical and noise disturbance are indirectly impacted and mitigation is implemented through specific licensing requirements.

4.5.6 Consideration of other sectoral activities in survey planning

Scotland’s marine area is shared by multiple sectors which have the potential to exert multiple pressures and may increase the likelihood of a net negative impact to the marine environment. This may compound impacts evident within an MRED and influence the benthic sampling requirements. The sectors which require consideration and example impacts are summarised in Table 4.8.

Where other sea user activity is prevalent within or near to an MRE development scheme, a redistribution of sampling may be required to stratify sampling effort according to differing activities and pressures or select suitable control sites. The likely zone of influence of such issues should be considered in survey designs. Certain classes of the other maritime and coastal activities have the potential to lead to chemical contamination as well as physical disturbance, others are limited simply to potential physical disturbance.

4.5.7 Consideration of on-the-coast or at sea operating factors

Benthic sampling tools and technologies vary in size, complexity and therefore usability, which can then compromise their suitability and impact the time and monetary costs involved. As such, there are operating factors to consider that will influence the benthic survey tools and technologies that are employed throughout MREDs. The benthic survey tools and technologies employed in MREDs globally tend to vary by sector and country therefore, equipment and sampling vessels should be selected that are both suitable for the sampling purpose and local conditions of Scottish waters. Conditions that may impact operating and sampling success in Scottish waters include tidal cycles (springs vs neaps effect on current flow and sea levels), short-term (weather) and temporal meteorological patterns (e.g., seasonal storms, cyclic weather events (i.e. North Atlantic Oscillation)). MREDs require effective sampling throughout their operational lifespan. The predicted increase in severity and longevity of weather events may hinder operational success, exacerbating conditions at sites located in exposed and remote marine areas with prevalent wind directions and strong tidal conditions.