Appendix 6 Benthic Subtidal Ecology – Baseline Environment

Appendix 6
Benthic Subtidal Ecology – Baseline Environment

6.1.        Desktop Study

  1. To inform this Scoping Report, an initial desk-based review of literature and data sources has been undertaken, which identified data sources which provide coverage of the site boundary. They have been used to inform the design of site-specific benthic subtidal ecology surveys, in order to provide adequate coverage of all areas and habitat types within the site boundary. They will also provide context to the site-specific data collected and will be reported in full within the Array Environmental Impact Assessment (EIA) Report. These are summarised in Apx Table 6.1   Open ▸ .

 

Apx Table 6.1:
 Summary of Key Desktop Datasets and Materials

Apx Table 6.1:  Summary of Key Desktop Datasets and Materials

 

6.2.        Site-specific Survey Data

  1. Site-specific benthic survey data were used to support this Scoping Report and were gathered across the site boundary in July 2022 (Appendix 7). These surveys were undertaken by Ocean Infinity, using the vessel ‘M/V Northern Maria’. The site-specific surveys consisted of Drop-Down Video (DDV) and still photography, grab sampling, and epibenthic beam trawling. There were a total of 80 DDV and 0.1 m2 Hamon grab sampling locations within the Array benthic subtidal ecology study area, and Day grab sampling (sediment chemistry) at ten of the 80 locations. In addition, ten 200 m long epibenthic (2 m) beam trawls were distributed across the representative sediment types within the Array benthic subtidal ecology study area to characterise the epifaunal communities present ( Apx Figure 6.1   Open ▸ ). A cod-end mesh of 5 mm was used in the epibenthic beam trawls.
  2. All 80 of the DDV sampling sites were successfully photographed and recorded in good quality. Of the 80 grab sample sites, 11 were excluded from analyses due to insufficient sample volume as a result of cobbles (S007, S008, S018, S023, S025, S029, S038, S042, S049, S052, and S070). Of the 80 DDV sites, three had no fauna recorded (S012, S026, and S064).

Apx Figure 6.1:
Location of Sampling Sites During the Site-Specific Benthic Surveys Conducted in July 2022

Apx Figure 6.1: Location of Sampling Sites During the Site-Specific Benthic Surveys Conducted in July 2022

6.3.        Baseline Characterisation

  1. This section provides an overview of the baseline for benthic subtidal ecology established through a desktop review and site-specific survey data collected to date by Ocean Infinity (2022a). 

6.3.1      Subtidal Sediments

  1. The EUSeaMap broadscale substrate data indicate the sediments within the site boundary area are significantly dominated by deep circalittoral sand (biotope classification: SS.SSa.Osa). There is one small area comprised of deep circalittoral coarse sediment (SS.SCS.OCS) located within the north-west of the area. Elsewhere in the regional benthic subtidal ecology study area, deep circalittoral sand is interspersed more evenly with deep circalittoral coarse sediment. 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. The subtidal sediments within the Array benthic subtidal ecology study area are illustrated in Apx Figure 6.2   Open ▸ .
  2. The subtidal benthic sediments recorded during the site-specific benthic surveys were classified into sediment types according to the Folk (1954) classification. The sediment composition through particle size analysis (PSA) sampled across the Array benthic subtidal ecology study area had limited variation and was mainly comprised of sand with an average content of 86.4%. Only three stations presented a dominant classification of gravel (>30% gravel). Similar to the EUSeaMap data, the site-specific benthic surveys indicate that the subtidal sediments within the site boundary area are dominated by sand with mixed sediments predominantly in the north-west ( Apx Figure 6.3   Open ▸ ).
  3. Site-specific geophysical surveys were conducted within the site boundary between March and July 2022. Seafloor interpretation was based on side scan sonar (SSS) and multibeam echosounder (MBES) data and aided the characterisation of the subtidal sediment baseline. The water depth ranged between 63.82 m and 88.66 m, with generally increasing depth from the north-west to the south-east. The bathymetry consists of gentle slopes which generally deepen towards the east, with larger sediment features running in a north/south direction and small sediment features running in a more east/west direction ( Apx Figure 6.4   Open ▸ ). The seafloor gradient is very gentle, with occasional higher slope angles and very steep slopes observed on wrecks.
  4. Consistent with the results of EUSeaMap data, the subtidal sediments observed during the site-specific geophysical surveys of the Array benthic subtidal ecology study area are dominated by sand. However, there were larger and more numerous patches of gravel and occasional diamicton (poorly sorted mixed sediments), including boulder fields, observed, mainly in the west ( Apx Figure 6.3   Open ▸ ). The results of the geophysical surveys therefore indicate a slightly less homogenous sediment composition than the broadscale EUSeaMap data, which is typically expected when drawing comparisons between broadscale interpolated data and detailed site-specific information ( Apx Figure 6.3   Open ▸ ). The seabed within the site boundary is relatively flat, generally deepening towards the east (as per paragraph 193). The widespread presence of megaripples and sand waves indicated some sediment mobility, while occasional furrows, mainly in the west, were indicative of erosion ( Apx Figure 6.5   Open ▸ ).

Apx Figure 6.2:
Predicted EUNIS Habitats from the EUSeaMap for the Site Boundary (EMODnet, 2019)

Apx Figure 6.2: Predicted EUNIS Habitats from the EUSeaMap for the Site Boundary (EMODnet, 2019)

Apx Figure 6.3:
Sediment Features and Boulder Fields within the Site Boundary

Apx Figure 6.3: Sediment Features and Boulder Fields within the Site Boundary

Apx Figure 6.4:
Bathymetry Within the Site Boundary

Apx Figure 6.4: Bathymetry Within the Site Boundary

Apx Figure 6.5:
Surficial Geology and Seabed Features Within the Site Boundary

Apx Figure 6.5: Surficial Geology and Seabed Features Within the Site Boundary

 

6.3.2      Subtidal Benthic Communites

  1. Initial 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 mixed sediment” and “Faunal communities of Atlantic circalittoral sand”. Preliminary biotope classifications within these broad classifications were also assigned, with the following biotopes identified: “Echinocyamus pusillus, Ophelia borealis, and Abra prismatica in circalittoral fine sand” and “A. prismatica, Bathyporeia elegans, and polychaetes in circalittoral fine sand”.
  2. The non-colonial faunal analysis of grab samples during the site-specific benthic surveys reported that annelids had the highest abundance and diversity, primarily sand mason worm Lanice conchilega and the bristleworm Spiophanes bombyx, followed by a range of mollusc and arthropod species. 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 Echinocyamus pusillus. Echinoderms represented the highest proportion of the total biomass collected during grab sampling. The colonial fauna was dominated by cnidarians and bryozoans.
  3. 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 (primarily fish), which contributed 67% of the total biomass, followed by echinoderms (15%) and bryozoans (7%).
  4. Annelids were the most abundant non-colonial fauna observed in still photographs, primarily L. conchilega, followed by cnidarians, while bryozoans had the highest coverage of the colonial fauna. Nevertheless, the faunal presence in the DDV and still photography surveys was generally sparse and comprised the following:
  • sand mason worm L. conchilega;
  • bryozoan Flustra foliacea;
  • symbiotic hermit crab Pagurus prideaux and anemone Adamsia palliata;
  • scattered colonies of cnidarians Epizoanthus;
  • echinoderms Asterias rubens, Echinus esculentus, Spatangus purpureus and Ophiura sarsii;
  • sea pen Pennatula phosphorea; and
  • ocean quahog Arctica islandica
  1. A brief 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 50.72 km, 56.77 km, and 61.6 km from the site boundary, respectively; see Apx Figure 6.5   Open ▸ ) is presented in Apx Table 6.2   Open ▸ . Other offshore wind farms in the vicinity of the Array include Inch Cape Offshore Wind Farm (86.9 km), the Hywind Buchan Deep Demonstration (72 km), and Neart na Gaoithe Offshore Wind Farm (105 km). Although further from the Array, these sites generally consisted of similar sediment classifications, with circalittoral sands and gravely sands with areas of mixed muddy sediment observed at Inch Cape (Inch Cape Offshore Limited, 2011), offshore circalittoral sand and offshore circalittoral mixed sediment recorded at Hywind (Statoil, 2013), and slightly gravelly muddy sand and circalittoral sandy mud recorded at Neart na Gaoithe (Mainstream Renewable Power, 2012).

 

Apx Table 6.2:
 Benthic Subtidal Ecology Community Overview from Seagreen 1 and Berwick Bank Site-Specific Benthic Subtidal Ecology Survey Data (Seagreen, 2012, Atkins, 2016, SSER, 2022)

Apx Table 6.2:  Benthic Subtidal Ecology Community Overview from Seagreen 1 and Berwick Bank Site-Specific Benthic Subtidal Ecology Survey Data (Seagreen, 2012, Atkins, 2016, SSER, 2022)

 

  1. As part of the Regional Seabed Monitoring Programme (RSMP), Cooper and Barry (2017) describe results of the baseline assessment of the UK’s macrobenthic infauna. Although the study was focussed on the aggregates industry, a “big data” approach was taken which collated data from across UK waters, including in proximity to the Array. This data was collated form various industries, including offshore wind farms, oil and gas, nuclear, and port and harbour sectors. Cooper and Barry (2017) categorised benthic macrofaunal communities into broad groups, based on similarities in their community composition.
  2. No RSMP infaunal samples have been taken within the Array benthic subtidal ecology study area itself, however, there were some in close proximity, to the west of the site boundary. The closest samples from the dataset were characterised by deep circalittoral sands and deep circalittoral coarse sediment and associated benthic infaunal communities of polychaetes (D2b, D2c and D2d faunal groups: Spionidae, Nephtydae, Lumbrineridae, Oweniidae, Cirratulidae, Capitellidae, Ampharetidae, Opheliidae, Magelonidae), bivalve molluscs (D2b and D2d faunal groups: Semelidae and Tellinidae) and nemerteans (D2b faunal group). Elsewhere in the regional benthic subtidal ecology study area, the Cooper and Barry (2017) dataset presents a mixture of deep circalittoral sands with deep circalittoral coarse sediment and associated benthic infaunal communities of polychaetes (C1a and C1b faunal groups: Spionidae, Glyceridae, Terebellidae, Capitellidae, and Phyllodocidae) and nemerteans (D2a faunal group). Within the Firth of Forth, deep circalittoral mud is present, which is associated with infaunal Nephtyidae communities (faunal group D2c: Nephtyidae, Spionidae, Ophelidae).
  3. These findings are in line with those of Sotheran and Crawford-Avis (2014) who identified Marine Nature Conservation Review (MNCR) habitats from samples in close proximity to the site boundary. Spiophanes bombyx aggregations in offshore sands (SS.SSa.OSa.[Sbom]) were identified in deep circalittoral sand and Spiophanes bombyx aggregations in offshore coarse sands (SS.SCS.OCS.[Sbom]) and polychaete-rich Galathea communities with encrusting bryozoans and other epifauna on offshore coarse sediments (SS.SCS.OCS.[PoGintBy]) were identified in deep circalittoral coarse sediments.
  4. Similarly, Pearce et al. (2014) identified Sabellaria spinulosa on stable circalittoral mixed sediment (SS.SBR.PoR.SspiMx), polychaete-rich Galathea communities with encrusting bryozoans and other epifauna on offshore circalittoral mixed sediment (SS.SMx.OMx.[PoGintBy]), and Spiophanes bombyx aggregations in offshore sands and coarse sands (SS.Ssa.Osa.[Sbom], and SS.SCS.OCS.[Sbom], respectively) in close proximity to the Array, albeit further inshore.

6.3.3      Sediment Contamination

  1. Ten of the 80 grab sample sites were selected for chemical analysis for the following contaminants:
  • metals;
  • organic content: total organic matter (TOM) and total organic carbon (TOC);
  • total hydrocarbon content (THC);
  • polycyclic aromatic hydrocarbons (PAH);
  • polychlorinated biphenyls (PCBs); and
  • organotins.
  1. The samples were tested for the following metals: aluminium, arsenic, barium, cadmium, chromium, copper, iron, lead, mercury, nickel, vanadium, and zinc. Overall, metal concentrations were low and varied little across the site boundary. There were no samples that exceeded the Cefas Action Level 1 thresholds.
  2. All the 80 grab sample sites were analysed for organic content in the form of TOM and TOC. Contents of TOM and TOC varied slightly, with an average of 0.8% (standard deviation (SD) = 0.3) and 0.2% (SD = 0.1), respectively. Concentrations of both were relatively consistent across the site boundary but were generally higher in the southern and eastern regions, which is generally consistent with areas of slightly higher proportions of fine sediments.
  3. THC concentrations were varied, but low, across the site boundary and were generally higher in the southern and eastern sections, again, generally aligned with the PSA data and higher proportions of fine sediments. THC concentration ranged between 6.21 µg/g to 13.7 µg/g, with an average of 10.51 µg/g (SD = 2.155).
  4. PAH concentrations were low overall but varied across the site boundary and were generally higher in the southern and eastern sections, albeit still low overall. This is in line with the PSA results for slightly higher quantities of sediment fines. Cefas Action Level 1 was not exceeded at any of the sample sites, with most samples below the limits of detection.
  5. Levels of PCBs and organotins (Dibutyltin and Tributyltin) were below the limit of detection at all ten sites sampled.

6.3.4      Designated Sites

  1. While the site boundary does not overlap with any protected sites that have been designated for benthic subtidal features, numerous sites occur within the regional benthic subtidal ecology study area ( Apx Table 6.3   Open ▸ ,. Apx Figure 6.6   Open ▸ ). These include Marine Protected Areas (MPAs), Marine Conservation Zones (MCZs) and Special Areas of Conservation (SACs). Sites of Special Scientific Interests (SSSIs) have not been listed here due to their distance from the Array and their intertidal features which would not be impacted by the Array.
  2. Using publicly available data supplied by the JNCC, EMODnet, and the Marine Scotland NMPi maps, there are no known Annex I sandbanks, mudflats, reefs, shallow inlets or bays, submerged or partially submerged sea caves, estuaries, or OSPAR threatened and declining habitats overlapping with the Array. As indicated in Apx Table 6.3   Open ▸ the closest designated site with benthic subtidal ecology features is the Firth of Forth Banks Complex MPA, which is located some 25 km from the Array area at its closest point. All other SACs, MCZs and MPAs are much further away (i.e. >50 km) and, therefore, unlikely to be affected by the Array.
  3. There were no Annex I features, including stony or biogenic reefs, recorded in the site-specific benthic surveys. There were two habitats and 13 species of conservation importance identified within the Array. 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 species), and dead man’s fingers A. digitatum (SBL). The remainder of the species were fish and shellfish and are presented in Appendix 8.
  4. The Likely Significant Effect (LSE) Screening Report includes 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 UK and transboundary European sites and features will be presented in the Report to Inform Appropriate Assessment (RIAA).

Apx Figure 6.6:
Sites Designated for Relevant Benthic Ecological Features and Other Offshore Infrastructure Within Close Proximity to the Site Boundary

Apx Figure 6.6: Sites Designated for Relevant Benthic Ecological Features and Other Offshore Infrastructure Within Close Proximity to the Site Boundary

Apx Table 6.3:
 Summary of Protected and/or Designated Sites with Relevant Benthic Subtidal Ecology in Proximity to the Array

Apx Table 6.3:  Summary of Protected and/or Designated Sites with Relevant Benthic Subtidal Ecology in Proximity to the Array