8.7. Baseline Environment

8.7.1. Overview of Baseline Environment

15. The following sections provide a summary of the benthic subtidal ecology baseline environment. The benthic subtidal ecology technical report, volume 3, appendix 8.1, includes full details of the analysis undertaken to develop the baseline and information on benthic subtidal ecology.

                        Regional Benthic Subtidal Ecology Study Area

16. The regional benthic subtidal ecology study area was characterised through a desktop review of key literature sources (presented in Table 8.6   Open ▸ ). Broadscale seabed substrate data indicates that, in terms of EMODnet sediment classifications, the regional benthic subtidal ecology study area is dominated by deep circalittoral sand (A5.27) and is interspersed with deep circalittoral coarse sediment (A5.15), which is characteristic of the North Sea (EMODnet, 2023) ( Figure 8.2   Open ▸ ). Other low energy habitats, such as deep circalittoral mud and circalittoral mixed sediments are recorded along the coast and within the Firth of Forth (EMODnet, 2023). Finer sediments, moderate energy circalittoral rock, circalittoral mixed sediments, and circalittoral sandy mud were recorded further inshore (EMODnet, 2023).
17. There were a diverse range of benthic species and communities identified within the regional benthic subtidal ecology study area by Axelsson et al. (2014), Pearce et al. (2014), Sotheran and Crawford-Avis (2013), Sotheran and Crawford-Avis (2014) and Cooper and Barry (2017), and from site-specific surveys undertaken for other offshore wind farms (see volume 3, appendix 8.1 for a full account and Table 8.8   Open ▸ for a summary). However, it should be noted that these datasets were based on areas further inshore and with more heterogenous sediment composition than that of the Array benthic subtidal ecology study area. Species and communities identified in the data sources listed in Table 8.6   Open ▸ and in the site-specific survey for the Array include polychaetes (particularly bristleworm Spiophanes bombyx), dead man’s fingers Alcyonium digitatum, and various echinoderms and bryozoans (such as hornwrack Flustra foliacea). A brief summary of the results of the site-specific surveys for the Array is provided in the paragraph 18 to 24.

Table 8.8: Overview of Benthic Subtidal Communities from other Projects within the Regional Benthic Subtidal Ecology Study Area

Figure 8.2: Subtidal Sediments within the Regional Benthic Subtidal Ecology Study Area (Source: EMODnet (2023))

                        Array Benthic Subtidal Ecology Study Area

18. Overall, the results from the site-specific geophysical and environmental surveys (see Table 8.7   Open ▸ of this chapter and volume 3, appendix 8.1, annex A) concluded that the Array benthic subtidal ecology study area was dominated by sand, classified as MC521 – Faunal communities of Atlantic circalittoral sand. Mixed sediments were present predominantly in the north-west and were classified as MC421 – Faunal communities of Atlantic circalittoral mixed sediment. This MC421 habitat decreased in abundance towards the south-east, only occurring occasionally and often associated with ripple features. The majority of sampling sites shared components of MC521 and MC421, albeit to a varying degree. Higher mud content, gravel and diamicton were observed in the central and south-eastern sections, however the Array benthic subtidal ecology study area was largely homogenous. The widespread presence of megaripples and sand waves indicated some sediment mobility, while occasional furrows, mainly in the west, were indicative of erosion. These results are in line with the EUSeaMap broadscale substrate data, which indicate that the Array benthic subtidal ecology study area is significantly dominated by deep circalittoral sand (A5.27) ( Figure 8.2   Open ▸ ).
19. Regarding sediment contamination, levels of Polychlorinated Biphenyls (PCBs) and organotins within the Array benthic ecology subtidal study area were below the limit of detection at all sampled sites. Similarly, metals were generally low, except for arsenic at sample site S002 (located at the northernmost tip of the Array benthic subtidal ecology study area). This value marginally exceeded the Norwegian Environment Agency (NEA) Good 2 threshold and the Canadian Environmental Quality Guidelines (CEQGs) threshold but was within the various other thresholds tested (such as the Cefas action levels) therefore is not considered of concern. Total Hydrocarbon Content (THC) varied across the Array benthic subtidal ecology study area and was generally higher in the southern and eastern areas. THC did not exceed any of the Dutch Rijksinstituut voor Volksgezondheid en Milieu (RIVM) intervention levels at any of the sampling sites and were lower than Oslo Paris Convention (OSPAR) background levels for the North Sea. Similarly, Polycyclic Aromatic Hydrocarbon (PAH) concentrations were low overall, with concentrations higher in the southern and eastern areas in the same trend as THC. There were no threshold values exceeded for individual PAHs but the sum of the Environmental Protection Agency (EPA) 16 compounds exceeded the lower threshold value for NEA Good 2 at sampling site S051 (located at the southernmost tip of the Array benthic subtidal ecology study area).
20. Biomass between grab sampling sites was varied, with six major phyla identified: Echinodermata, Mollusca, Annelida, Arthropoda, Cnidaria and Bryozoa. Echinoderms comprised the majority of the biomass within the grab samples (65%), which is largely due to the purple heart urchin Spatangus purpureus and sea potato Echinocardium cordatum occurring at several grab sampling sites. The phyletic composition was dominated by annelids, mainly sand mason worm Lanice conchilega and S. bombyx. The phyletic composition of sessile colonial fauna was dominated by cnidarians and bryozoans, with cnidarians representing the highest number of taxa and bryozoans the highest number of colonies.
21. The most abundant non-colonial fauna identified in the DDV and photography survey were annelids and cnidarians, representing 39% and 28% of total abundance, respectively. Cnidarians covered the largest surface area within the imagery, with a total contribution of 48%, followed by bryozoans and bryozoans/cnidarians at 47% and 5%, respectively.
22. Within the trawl samples, arthropods dominated the phyletic composition of non-colonial fauna, and cnidarians represented the highest number of individuals and colonies of the sessile colonial fauna. The total faunal biomass was dominated by chordates, with the most abundant chordate being the long rough dab Hippoglossoides platessoides (discussed further in the volume 3, appendix 9.1).
23. Species richness, diversity, and evenness were relatively low across grab sampling sites, which could be explained by the limited variation in sediment composition. The number of taxa and the number of individuals ranged between 14 to 34 taxa and 28 to 143 individuals per 0.1 m2. There were two statistical groups produced in the Similarity Proofing Algorithm (SIMPROF) analysis on untransformed macrofaunal data, with the majority of grab samples sites within group b ( Figure 8.3   Open ▸ ). The similarity explored in the Non-Metric Multidimensional Scaling (NMDS) plot presented a stress value of 0.21 ( Figure 8.3   Open ▸ ). The SIMPROF analysis conducted with a square root transformation resulted in five statistically distinct groups, with the majority of sample sites in group e, and a stress value of 0.27 ( Figure 8.4   Open ▸ ). These results were indicative of homogeneity between sampling sites, with the gravel and mud proportions being the main driver for faunal community diversity. The results of the Biota-Environment Matching and Stepwise Test (BEST) indicated that mud and gravel were the variables that best explained the spatial distribution of fauna (rho = 0.29, P = 0.01), and were statistically significant variables.

Figure 8.3: NMDS Plot Based on Untransformed Non-Colonial Faunal Composition from Macrofaunal Grab Sampling Sites within the Array Benthic Subtidal Ecology Study Area

Figure 8.4: NMDS Plot Based on Square Root Transformed Non-Colonial Faunal Composition from Macrofaunal Grab Sampling Sites within the Array Benthic Subtidal Ecology Study Area

24. There were no Annex I habitats identified within the site-specific survey, however there were several habitats and species of conservation interest recorded, which are summarised in Table 8.9   Open ▸ . These include two habitats and various species, such as horse mussel Modiolus modiolus, sea tamarisk Tamarisca tamarisca, ocean quahog Arctica islandica, dead man’s fingers, and phosphorescent sea pen Pennatula phosphorea. These habitats and species of conservation interest are further discussed in section 8.7.3, where they have been carried forward as IEFs for the assessment.

Table 8.9: Benthic Habitats and Species of Conservation Importance Identified during the Site-Specific Environmental Survey

8.7.2. Designated Sites

25. Designated sites and relevant qualifying interest features identified for the benthic subtidal ecology Array EIA Report chapter are described in Table 8.10   Open ▸ and presented in Figure 8.5   Open ▸ . These include an MPA and three SACs. SSSIs have not been listed here due to their distance from the Array benthic subtidal ecology study area and their intertidal features which would not be impacted by the Array. For example, the closest SSSIs with benthic ecological designations are the Tayport Tentsmuir Coast SSSI (124 km), Berwickshire Coast Intertidal SSSI (126 km), and the Firth of Forth SSSI (127 km), which are designated for various intertidal habitats, such as mudflats, saline lagoons and rocky shores. These SSSIs are therefore all outside potential ZoIs for impacts associated with the Array.
26. None of the four designated sites within the regional benthic subtidal ecology study area overlap with the Array benthic subtidal ecology study area (see Figure 8.5   Open ▸ ). For example, the closest designated site with qualifying benthic ecological features is the Firth of Forth Banks Complex MPA, which is located a minimum of 25 km from the Array benthic subtidal ecology study area. Due to this large distance and the lack of mobile qualifying interest features, this MPA is unlikely to be affected by the Array. Using this logic, the remaining three designated sites are also unlikely to be impacted by the Array, especially considering their increased distance from the Array and any potential ZoIs (see Table 8.10   Open ▸ ). In addition, two of the qualifying interest features of the Firth of Forth Banks Complex MPA have already been included as IEFs: the ocean quahog and Offshore subtidal sands and gravels, and have therefore been included as part of the assessment ( Table 8.11   Open ▸ ).

Table 8.10: Designated Sites and Relevant Qualifying Interest Features for the Benthic Subtidal Ecology Array EIA Report Chapter

Figure 8.5: Designated Sites Relevant to Benthic Subtidal Ecology

8.7.3. Important Ecological Features

27. For the purposes of the benthic subtidal ecology EIA, IEFs have been identified using best practice guidelines provided by the Chartered Institute for Ecology and Environmental Management (CIEEM) (2022). The potential impacts of the Array which have been scoped into the assessment (see section 8.8) have been assessed against the IEFs The IEFs assessed are those that are considered to be important and potentially impacted by the Array. Importance may be assigned due to quality or extent of habitats, habitat or species rarity, or the extent to which they are threatened (CIEEM, 2022). For a species or habitat to be considered an IEF, they must have a specific biodiversity importance recognised through international or national legislation or through local, regional, or national conservation plans e.g. Annex I habitats under the Habitats Directive, OSPAR protected habitats and species, National Biodiversity Plan or the Marine Strategy Framework Directive, UK Biodiversity Action Plan (BAP), Scottish PMFs, and the Scottish Biodiversity List (SBL).
28. As highlighted in Table 8.9   Open ▸ , individual horse mussels were identified across the survey, however no horse mussel beds were recorded. Therefore, as only the horse mussel beds themselves are of conservation importance (PMF, SBL and OSPAR habitats), this species will not be carried forward in the IEF evaluation. Similarly, P. phosphorea (SBL) was identified in multiple sampling sites, however the closely associated sea-pen and burrowing megafauna (OSPAR) and burrowed mud (PMF) habitats were not identified. Thus, only the SBL designation for the P. phosphorea itself will be taken forward in the IEF evaluation.
29. Table 8.11   Open ▸ lists all the IEFs within the Array benthic subtidal ecology study area. The main habitats identified throughout the Array benthic subtidal ecology study area comprise of Offshore subtidal sands and gravels and Subtidal sands and gravels.

Table 8.11: IEFs within the Array Benthic Subtidal Ecology Study Area

8.7.4. Future Baseline Scenario

30. The EIA Regulations require that a “a description of the relevant aspects of the current state of the environment (baseline scenario) and an outline of the likely evolution thereof without implementation of the project as far as natural changes from the baseline scenario can be assessed with reasonable effort, on the basis of the availability of environmental information and scientific knowledge” is included within the Array EIA Report.
31. If the Array does not come forward, the ‘without development’ future baseline conditions are described within this section.
32. In addition to the effects of climate change on the marine environment, variability and long term changes in physical processes may cause direct and indirect effects to benthic habitats and communities in the mid to long term future (Department of Energy and Climate Change (DECC), 2016). The best evidence indicates that long term changes to benthic ecology may be related to long term changes in the climate or in nutrients (DECC, 2016), with shifts in abundances and species composition being driven by climatic processes. Benthic communities are also influenced by anthropogenic activities, such as pollution, contamination, and seabed disturbing activities such as dredging, commercial fishing, and development. A scientific review by the Marine Climate Change Impacts Partnership (MCCIP) concluded that climatic processes both directly (e.g. winter mortality), and indirectly (e.g. via hydrographic conditions), influence the abundance and species composition of seabed communities (MCCIP, 2020). In turn, alteration to seabed communities could impact rates and timing of processes such as nutrient cycling, planktonic larval supply, and organic waste assimilation (MCCIP, 2020). Recently, the Department for Environment, Food, and Rural Affairs (DEFRA) has centred their focus on the risk of climate change to ecosystem services on the following topics:

• INNS and their likely detriment to native communities and ecosystems;
• the increased risk to species of disease from new pathogens as their distributions shift; and
• the impacts on areas of high biodiversity value in the coastal zone from increased storms and erosion (HM Government, 2022).

33. Overall, localised changes in community assemblage may occur due to pollution, contamination, and anthropogenic seabed disturbance and erosion (DECC, 2016, HM Government, 2022). DEFRA also highlighted that the risks associated with INNS, ocean acidification, and higher water temperatures are linked to climatic changes (HM Government, 2022), which could also have impacts on benthic subtidal ecology on a wider scale. However, the potential pressures described are unlikely to result in any significant changes to substrate type, which is a key driver of species assemblages and biotope classification. Nonetheless, it is difficult to define, for certain, how the baseline will evolve in the future, particularly at the species-level.

8.7.5. Data Limitations and Assumptions

34. The data sources used in this chapter are detailed in Table 8.6   Open ▸ and volume 3, appendix 8.1. The desktop data used are the most up to date publicly available information which can be obtained from the applicable data sources as cited. Data that have been collected are based on existing literature and have been informed through consultation with stakeholders.
35. Site-specific surveys were undertaken to characterise the benthic subtidal ecology baseline (see Table 8.7   Open ▸ ). However, it should be noted that there is a small possibility for the benthic communities to have developed and evolved in the intervening period since the site-specific surveys were carried out in 2022. Nonetheless, as the surveys were conducted less than five years prior to submission of this EIA Report, the results are considered to be fully valid. The sampling design and data collection have provided robust data on the benthic communities within the Array benthic subtidal ecology study area, however, interpreting these data has its limitations. It is often difficult to interpolate data collected from discrete sample locations to cover a very extensive area and define the precise extent of each biotope. Benthic communities generally show a transition from one biotope to another and therefore boundaries indicate where communities grade into one another rather than where one ends, and another begins. The classification of the community data into biotopes is not always straightforward, as some communities do not readily fit the available descriptions in the biotope classification system. However, this site-specific study does provide a suitable baseline characterisation which describes the main habitats and communities within the Array benthic subtidal ecology study area.