6.1. Benthic Subtidal EcologyBenthic Subtidal Ecology
6.1.1. IntroductionIntroduction
- This section of this Scoping Report presents the relevant benthic subtidal ecology aspects of the Array and considers the scope of assessment on benthic subtidal ecology from the construction, operation and maintenance, and decommissioning of the Array.
6.1.2. Study AreaStudy Area
- Two study areas are defined to inform the characterisation of the baseline environment for benthic subtidal ecology:
- Array benthic subtidal ecology study area, which is defined as the area encompassed by the site boundary (see Figure 6.1 Open ▸ ). The site-specific benthic subtidal ecology surveys were undertaken within this area, the results of which were used to inform the baseline characterisation and identify benthic receptors which could be potentially impacted by the Array; and
- The regional benthic subtidal ecology study area, which is defined as the area encompassing the wider North Sea (see Figure 6.1 Open ▸ ). The boundaries for this regional benthic subtidal ecology study area were adapted from the SMP Assessment region: East Region, to include an area to the south of the site boundary which has the potential to be impacted by indirect effects. Desktop data sources have been used to characterise the regional benthic subtidal ecology study area, which will, overall, provide wider context to the site-specific data collected within the Array benthic subtidal ecology study area in 2022 (see Appendix 7).
6.1.3. Baseline EnvironmentBaseline Environment
- The benthic subtidal ecology baseline environment of the Array is summarised briefly in this section, with a detailed description provided in Appendix 6. The site-specific survey data collected in 2022 (Appendix 7), and the comprehensive desktop information and data sources outlined in Appendix 6 ensures a robust and up to date characterisation of the benthic subtidal ecology baseline for the purposes of the Array Environmental Impact Assessment (EIA) Report.
Subtidal sediments
- The EUSeaMap data indicate that deep circalittoral sand (JNCC Marine Habitat Classification (MHC): SS.SSa.OSa) dominates the site boundary encompassing the Array. There is one small area comprised of deep circalittoral coarse sediment (SS.SCS.OCS) located within the north-west of the site boundary. These are illustrated in Apx Figure 6.1 Open ▸ . Deep circalittoral sand is interspersed more evenly with deep circalittoral coarse sediment elsewhere in the regional benthic subtidal ecology study area, while deep circalittoral mud (SS.SMu.OMu) and circalittoral mixed sediments (SS.SMx.CMx) are mainly present along the coast and within the Firth of Forth.
Figure 6.1: Benthic Subtidal Ecology Study Areas
- Limited variation in sediment composition was reported during the site-specific benthic surveys across the Array benthic subtidal ecology study area. The substrate mainly comprises sand, with several sites revealing higher gravel content. Sand was the dominant sediment fraction with an average content of 86.4%. Similarly, results of the site-specific benthic surveys indicated that two broad subtidal habitats characterised the Array benthic subtidal ecology study area: “Faunal communities of Atlantic circalittoral sand” and “Faunal communities of Atlantic circalittoral mixed sediment”.
- Site-specific geophysical data have been collected across the site boundary (Appendix 7). These show that the seabed within the Array benthic subtidal ecology study area is characterised by sand, with numerous patches of gravel and occasional diamicton observed, mainly in the west ( Figure 6.2 Open ▸ ). The widespread presence of megaripples and sand waves indicated some degree of sediment mobility, while occasional furrows, mainly in the west, were indicative of erosion. The water depth ranged between 63.82 m and 88.66 m, with a general increase in depth towards the east. The seafloor gradient demonstrates gentle slopes that also generally deepen towards the east of the site boundary.
Subtidal benthic communities
- As outlined above, site-specific survey data indicated the sediment composition comprised “Faunal communities of Atlantic circalittoral sand” and “Faunal communities of Atlantic circalittoral mixed sediment” (see paragraph 323). Grab sample data indicated the presence of two subtidal habitats within the Array benthic subtidal ecology study area. These were “Echinocyamus pusillus, Ophelia borealis, and Abra prismatica in circalittoral fine sand” (JNCC MHC SS.SSa.CFiSa.EpusOborApri), and “A. prismatica, Bathyporeia elegans, and polychaetes in circalittoral fine sand” (SS.SSa.CFiSa.ApriBatPo).
- The results of the site-specific benthic survey recorded high abundances of annelids, primarily sand mason worm Lanice conchilega and the bristleworm Spiophanes bombyx. There were 196 non-colonial taxa recorded from the grab samples, with the most abundant being L. conchilega, S. bombyx, bivalve A. prismatica, bristleworm Scoloplos armiger and pea urchin E. pusillus. The colonial fauna was dominated by cnidarians and bryozoans, while echinoderms comprised the majority of the total biomass collected during grab sampling. The faunal analysis of the epibenthic beam trawling indicated that the non-colonial phyletic composition was dominated by arthropods, with 46 taxa recorded. The colonial fauna identified comprised cnidarians, bryozoans and porifera. The total fauna recorded in the trawls was dominated by chordates (i.e. fish), which contributed 67% of the total biomass, followed by echinoderms (15%) and bryozoans (7%).
- Faunal presence in the drop-down video (DDV) and still photographs recorded during the site-specific benthic surveys was generally sparse and species composition consisted of the following: L. conchilega, bryozoans and cnidarians, echinoderms, sea pen Pennatula phosphorea, ocean quahog Arctica islandica, and the symbiotic hermit crab Pagarus prideaux with anemone Adamsia palliata.
- An overview of the benthic communities recorded within surveys for the nearby Seagreen 1 (formerly known as Seagreen Alpha and Bravo), Berwick Bank, and Kincardine Offshore Wind Farms (located between 50 km and 62 km from the site boundary) is presented in Table 6.1 Open ▸ . Further detail on other desktop data sources from the regional benthic subtidal ecology study area is set out in Appendix 6.
Figure 6.2: Sediment Features and Boulder Fields Within the Site Boundary
Table 6.1: Benthic Subtidal Ecology Community Overview from Seagreen 1 and Berwick Bank Site-Specific Benthic Subtidal Ecology Survey Data (Seagreen, 2012, Atkins, 2016, SSER, 2021)
Sediment contamination
- Ten of the 80 grab samples from the site-specific benthic surveys were tested for contaminants such as metals, total organic matter (TOM), total organic carbon (TOC), total hydrocarbon content (THC), polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCBs) and organotins.
- Levels for all contaminants within the site boundary were low overall, and concentrations of TOM, TOC, THC, and PAH were slightly higher in the southern and eastern regions, albeit still low. Levels of metals and PAH were below Cefas Action Level 1. Similarly, concentrations of PAH, PCBs, and organotins were below the limit of detection in most samples.
Designated sites
- The Array does not overlap with any protected sites that have been designated for benthic subtidal features. Numerous sites have been identified as occurring within the regional benthic subtidal ecology study area (Apx. Table 6.3 and Apx Figure 6.6 Open ▸ ). These include Marine Protected Areas (MPAs), Marine Conservation Zones (MCZs) and Special Areas of Conservation (SACs). However, due to the distance between the Array and these designated sites (i.e. the closest designated site is over 25 km from the Array), impacts on benthic subtidal features of these sites are unlikely to occur.
- There were no Annex I features, including stony or biogenic reefs, recorded in the site-specific benthic surveys. However, there were two habitats and 13 species of conservation importance recorded. The habitats included one Priority Marine Feature (PMF) habitat: offshore subtidal sands and gravels, and one Scottish Biodiversity List (SBL) habitat: subtidal sands and gravels. The species included the sea pen P. phosphorea and associated burrowed mud PMF, hydroid Tamarisca tamarisca (SBL), ocean quahog (PMF and OSPAR (Convention for the Protection of the Marine Environment of the North-East Atlantic) species), and dead man’s fingers A. digitatum (SBL).
- The Likely Significant Effect (LSE) Screening Report will include a full screening of National and European designated sites with qualifying interest features relevant to benthic subtidal ecology, that may be impacted by the Array. The information to support the assessment of the National Site Network and transboundary European sites and features will be presented in the Report to Inform Appropriate Assessment (RIAA), as part of the Habitat Regulations Assessment (HRA) process.
6.1.4. Potential Array ImpactsPotential Array Impacts
- Potential impacts on benthic subtidal ecology which may occur during the construction, operation and maintenance, and decommissioning phases of the Array in the absence of designed in measures have been identified in Table 6.2 Open ▸ .
Table 6.2: Potential Impacts Identified for Benthic Subtidal Ecology in the Absence of Designed In Measures
6.1.5. Designed In MeasuresDesigned In Measures
- The following designed in measures have been considered in the identification of potential impacts that have been scoped into the Array assessment, including how these can reduce potential for impact ( Table 6.4 Open ▸ ):
- the development of, and adherence to, an appropriate Code of Construction Practice (CoCP);
- the development of, and adherence to, an EMP, including a Marine Pollution Contingency Plan (MPCP) and INNSMP; and
- the development of, and adherence to a Decommissioning Programme.
- The significance of effects on benthic subtidal ecology may result in the requirement for additional mitigation measures. This will be consulted upon with the statutory consultees throughout the EIA process.
6.1.6. Relevant ConsultationsRelevant Consultations
- A summary of the key points of agreement with relevant stakeholders and Statutory Nature Conservation Bodies (SNCBs) during the Array Scoping workshop undertaken in November 2022 is presented in Table 6.3 Open ▸ .
Table 6.3: Summary of Key Consultation on the Scoping Assessment for the Array
6.1.7. Potential Impacts After the Implementation of Designed In MeasuresPotential Impacts After the Implementation of Designed In Measures
- Table 6.4 Open ▸ outlines the impacts which have been scoped into the Array assessment alongside a description of any additional analyses (e.g. modelling) that will be required to enable a full assessment of the impacts.
- Table 6.5 Open ▸ describes the potential impacts to benthic subtidal ecology that are proposed to be scoped out of the assessment at this stage.
Table 6.4: Impacts Proposed to be Scoped Into the Array Assessment for Benthic Subtidal Ecology. Project Phase Refers to Construction (C), Operation and Maintenance (O) and Decommissioning (D) Phase of the Array
Table 6.5: Impacts Proposed to be Scoped Out of the Array Assessment for Benthic Subtidal Ecology