Sensitivity of the receptor

366. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.19   Open ▸ and paragraphs 159 to 165).
367. Overall, the dead man’s fingers IEF and sea tamarisk IEF are deemed to be of low vulnerability, medium recoverability, and regional value. The sensitivities of the receptors are, therefore, considered to be low.
368. Overall, all other IEFs are deemed to be of high vulnerability, low recoverability, and national and regional value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

369. Overall, for the dead man’s fingers IEF and sea tamarisk IEF, the cumulative magnitude of impact is deemed to be low, and the sensitivities of the receptors are considered to be low. Based on Table 8.16   Open ▸ , the cumulative effect will, therefore, be of negligible to minor beneficial significance. Based on expert judgement and adopting a precautionary approach, the cumulative effect has been concluded to be of minor beneficial significance, which is not significant in EIA terms.
370. For all other IEFs, the cumulative magnitude of impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the effect will, therefore, be of minor to moderate significance. The potential for increased biodiversity as a result of this impact could be considered to be beneficial, however introduction of hard substrates would represent some small-scale habitat loss for these IEFs. Given the low footprint of long term habitat loss with respect to the Tier 3 projects and the North Sea as a whole, and the widespread availability of alternative suitable habitat, the cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

371. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.

Effects to benthic subtidal ecology due to removal of hard substrates

372. The removal of artificial hard substrates in the decommissioning phase of the Array and other projects may affect the established benthic community upon these structures, with the seabed returning to its previous sandy sediments. For the purposes of this EIA Report, this effect has been assessed using the tiered approach outlined in section 8.12.1. The plans and projects screened into the CEA for this impact and their respective Tiers are outlined in Table 8.23   Open ▸ .

                        Tier 1

                        Decommissioning phase

Magnitude of impact

373. There was one Tier 1 project identified with potential for cumulative effects associated with this impact:

• the decommissioning phase of the Proposed offshore export cable corridor(s) ( Table 8.23   Open ▸ ).

374. The MDS for the Array alone accounts for up to a total of 19.27 km2 of artificial hard substrates to be removed from the seabed during the decommissioning phase, which represents up to 2.25% of the total Array benthic subtidal ecology study area ( Table 8.12   Open ▸ ). In addition, the MDS accounts for the removal of hard substrate in the water column, such as floating wind turbine foundations, anchor mooring lines, and dynamic cables ( Table 8.12   Open ▸ ). As per the justification presented in Table 8.12   Open ▸ for the Array alone, the MDS for this impact is the complete removal of all infrastructure installed on the seabed and in the water column in the Array benthic subtidal ecology study area, as this represents the largest potential impact. These hard substrates include:

• mooring lines and anchors on the seabed;
• OSP foundations;
• inter-array and interconnector cable protection and cable crossing protection;
• subsea junction boxes;
• scour protection for mooring lines, anchors, OSP foundations, and subsea junction boxes; and
• floating wind turbine foundations in the water column.

375. It should be noted that the decommissioning strategy is not yet defined, and cable protection, cable crossing protection, and scour protection may potentially be left in situ. Anchors will also be removed or cut on or at the seabed and left in situ, however, are considered unlikely to contribute to this impact as they will be a significant depth below the seabed. Leaving cable protection, cable crossing protection, and scour protection in situ represents the MDS in the decommissioning phase for ‘Long term habitat loss and disturbance’ and has been assessed as such in paragraphs 282 et seq. In reality, if this infrastructure remains in situ, the MDS presented here will be an overestimation of the area of hard substrates removed.
376. There is currently no publicly available information available on the footprint of hard substrates installed at the Proposed offshore export cable corridor(s). However, given that it is a HVDC subsea power cable project, the area of hard structures installed will be of a significantly lesser extent than that represented by the MDS for the Array alone (see previous paragraph). The cumulative magnitude of impact of the Array with this Tier 1 project is therefore not expected to represent a material additional impact to that defined for the assessment of the Array alone (section 8.11).
377. Overall, for all IEFs, the impact is predicted to be of local spatial extent, long term duration, continuous, and of low reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the receptor

378. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.19   Open ▸ and paragraphs 94 to 97).
379. Overall, all IEFs except dead man’s fingers and sea tamarisk are deemed to be of low vulnerability, high recoverability, and national and regional value. The sensitivities of the receptors are, therefore, considered to be low.
380. In contrast however, the dead man’s fingers IEF and sea tamarisk IEF are deemed to be of high vulnerability, medium recoverability, and regional value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

381. Overall, for the dead man’s fingers IEF and sea tamarisk IEF, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the cumulative effect will, therefore, be of minor to moderate significance. Given the low footprint of hard substrates to be removed during the decommissioning phase (2.25% of the Array benthic subtidal ecology study area, and a presumably lower value for the Proposed offshore export cable corridor(s)) and the widespread availability of alternative suitable habitat, the cumulative effect will therefore be of minor adverse significance, which is not significant in EIA terms.
382. For all other IEFs, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be low. Based on Table 8.16   Open ▸ , the cumulative effect will, therefore, be of negligible to minor adverse significance. Based on expert judgement and adopting a precautionary approach, the cumulative effect has been concluded to be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

383. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.

                        Tiers 2 and 3

384. There were no Tier 1 or Tier 2 projects identified with the potential to result in cumulative effects associated with this impact ( Table 8.23   Open ▸ ).

Increased Risk of introduction or spread of INNS

385. Vessels used during the construction and operation and maintenance phases of the Array and the other projects could inadvertently transport INNS. This impact is related to the impact of ‘Colonisation of hard substrates’, which may lead to an increased risk of potential habitat that could be colonised by INNS. For the purposes of this EIA Report, this effect has been assessed using the tiered approach outlined in section 8.12.1. The plans and projects screened into the CEA for this impact and their respective Tiers are outlined in Table 8.23   Open ▸ .

                        Tier 1

                        Construction phase

Magnitude of impact

386. There were two Tier 1 projects identified with potential for cumulative effects associated with this impact:

• the construction and operation and maintenance phases of the Proposed offshore export cable corridor(s); and
• the operation and maintenance phase of the Eastern Green Link 2 ( Table 8.23   Open ▸ ).

387. At the time of writing this EIA Report, there was no Offshore EIA Report available for the Proposed offshore export cable corridor(s). However, given that these two projects are both HVDC subsea power cables, there will be fewer vessel trips associated with their overlapping phases than those associated with the site preparation and construction activities of the Array. Similarly, as assessed above in ‘Colonisation of hard substrates’, there will be fewer hard substrates (with the potential for colonisation by INNS) installed for the Tier 1 projects in comparison to the Array.
388. The MDS for the Array accounts for up to 7,902 vessel round trips over the course of the site preparation and construction phase, with up to 97 vessels on site at any one time ( Table 8.12   Open ▸ ). These provide vectors for the potential introduction of INNS into the habitats within the Array benthic subtidal ecology study area. In addition, the installation of hard substrate on the seabed and in the water column throughout the construction phase could provide new habitat for INNS to colonise. There were no values of vessel movements provided within the Environmental Appraisal Report for the Eastern Green Link 2, however the impact of increased risk of INNS was assessed as having negligible/minor significance (National Grid Electricity Transmission and Scottish Hydro Electric Transmission plc, 2022). The cumulative magnitude of the Array with the Tier 1 projects is not expected to represent a material additional impact to that defined for the assessment of the Array alone (section 8.11).
389. Many of the vessels associated with the Tier 1 projects and the Array are likely to come to and from the vicinity of the Array benthic subtidal ecology study area. Therefore, the potential for introduction of INNS from outside this region is reduced.  
390. As described in Table 8.17   Open ▸ , an INNSMP will be implemented, which aims to manage and reduce the potential risk of introduction and spread of INNS as far as reasonably practicable. In addition, all vessels associated with the Array will be required to comply with the IMO ballast water management guidelines, which will help reduce the risk of potential introduction and spread of INNS as far as practicable. Adherence to the IMO guidelines is also listed as an designed in mitigation commitment for the Eastern Green Link 2 (National Grid Electricity Transmission and Scottish Hydro Electric Transmission plc, 2022), and it is likely that the same will apply to the Proposed offshore export cable corridor(s).
391. Overall, for all IEFs, the impact is predicted to be of local spatial extent, medium term duration over the site preparation and construction phase, intermittent (in terms of invasions), and of low reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the receptor

392. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.21   Open ▸ and paragraphs 188 to 191).
393. Overall, all IEFs are deemed to be of high vulnerability, low recoverability, and regional to national value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

394. Overall, for all IEFs, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the effect will, therefore, be of minor to moderate significance. Given the low footprint of hard substrates to be installed in the Tier 1 projects that could be colonised by INNS, and the designed in mitigation measure of an INNSMP, the cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

395. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.

                        Operation and maintenance phase

Magnitude of impact

396. There were two Tier 1 projects identified with potential for cumulative effects associated with this impact:

• the operation and maintenance and decommissioning phases of the Proposed offshore export cable corridor(s); and
• the operation and maintenance and decommissioning phases of the Eastern Green Link 2 ( Table 8.23   Open ▸ ).

397. At the time of writing this EIA Report, there was no Offshore EIA Report available for the Proposed offshore export cable corridor(s). However, given that these two projects are both HVDC subsea power cables, there will be fewer vessel trips associated with operation and maintenance activities than those of the Array. Similarly, as assessed above in ‘Colonisation of hard substrates’, there will be fewer hard substrates (with the potential for colonisation by INNS) installed for the Tier 1 projects in comparison to the Array.
398. The MDS for the Array accounts for up to 17,780 vessel round trips over its 35 year lifecycle, or 508 round trips per year ( Table 8.12   Open ▸ ). There may be up to 31 vessels on site at any one time. As above for the site preparation and construction phase, these vessels provide vectors for the potential introduction of INNS into the habitats within the Array benthic subtidal ecology study area. In addition, the installation of up to 19.27 km2 of artificial hard substrate in the construction phase could provide new habitat for INNS to colonise throughout the lifecycle of the Array. There were no values of vessel movements provided within the Environmental Appraisal Report for the Eastern Green Link 2, however the impact of increased risk of INNS was assessed as having negligible/minor significance (National Grid Electricity Transmission and Scottish Hydro Electric Transmission plc, 2022). The cumulative magnitude of the Array with the Tier 1 projects is not expected to represent a material additional impact to that defined for the assessment of the Array alone (section 8.11).
399. As above for the site preparation and construction phase, many of the vessels within the operation and maintenance phase are likely to come to and from the vicinity of the Array benthic subtidal ecology study area. Therefore, the risk of introduction of INNS from outside this region is reduced.
400. As above for the site preparation and construction phase, the implementation of an INNSMP is a designed in measure which aims to manage and reduce the potential risk of introduction and spread of INNS as far as reasonably practicable ( Table 8.17   Open ▸ ). As above, all vessels will be required to comply with the IMO ballast water management guidelines, which will help reduce the risk of potential introduction and spread of INNS as far as practicable.
401. Overall, for all IEFs, the cumulative impact is predicted to be of local spatial extent, long term duration, intermittent (in terms of invasions), and of low reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the receptor

402. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.21   Open ▸ and paragraphs 188 to 191).
403. Overall, all IEFs are deemed to be of high vulnerability, low recoverability, and regional to national value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

404. Overall, for all IEFs, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the effect will, therefore, be of minor to moderate significance. Given the low footprint of hard substrates to be installed in the Tier 1 projects that could be colonised by INNS, and the designed in mitigation measure of an INNSMP, the cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

405. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.

                        Tier 2

                        Site preparation and construction phase

Magnitude of impact

406. In addition to the Tier 1 projects, there was one Tier 2 project identified with potential for cumulative effects associated with this impact: Morven Offshore Wind Farm ( Table 8.23   Open ▸ ). Like the Array, vessel movement at the Morven Offshore Wind Farm represents a vector for INNS transport, and hard substrates installed represent potential new habitat for INNS to colonise.
407. The MDS for the Array accounts for up to 7,902 vessel round trips over the course of the site preparation and construction phase, with up to 97 vessels on site at any one time ( Table 8.12   Open ▸ ). These provide vectors for the potential introduction of INNS into the habitats within the Array benthic subtidal ecology study area. In addition, the installation of hard substrate on the seabed and in the water column throughout the construction phase could provide new habitat for INNS to colonise. There were no values of vessel movements provided within the Scoping Report for Morven Offshore Wind Farm, however the impact was scoped in (Morven Offshore Wind Limited, 2023). Given the higher number of wind turbines and energy generation capacity of the Array in comparison to Morven Offshore Wind Farm ( Table 8.22   Open ▸ ), it is likely that there may be more vessel movements and potential for introduction of INNS associated with the Array. The cumulative magnitude of impact in the Tier 2 assessment is therefore not expected to represent a material additional impact to that defined for the assessment of the Array alone (section 8.11). Further, vessel movements associated with the Morven Offshore Wind Farm and the Array may follow similar routes and vessels associated with the Array may pass through the Morven Offshore Wind Farm. However, vessels associated with both will be required to comply with an INNSMP, which includes the IMO ballast water management guidelines, which help reduce the risk of potential introduction and spread of INNS as far as practicable ( Table 8.17   Open ▸ ).
408. As above for the Tier 1 assessment, many of the vessels are likely to come to and from the vicinity of the Array benthic subtidal ecology study area. Therefore, the potential for introduction of INNS from outside this region is reduced.
409. Overall, for all IEFs, the cumulative impact is predicted to be of local spatial extent, medium term duration over the site preparation and construction phase, intermittent (in terms of invasions), and of low reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the receptor

410. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.21   Open ▸ and paragraphs 188 to 191).
411. Overall, all IEFs are deemed to be of high vulnerability, low recoverability, and regional to national value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

412. Overall, for all IEFs, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the effect will, therefore, be of minor to moderate significance. Given the low footprint of hard substrates to be installed in the Tier 2 projects that could be colonised by INNS, and the designed in mitigation measure of an INNSMP, the cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

413. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.

                        Operation and maintenance phase

Magnitude of impact

414. In addition to the Tier 1 projects, there was one Tier 2 project identified with potential for cumulative effects associated with this impact: Morven Offshore Wind Farm ( Table 8.23   Open ▸ ). Like the Array, vessel movement at the Morven Offshore Wind Farm represents a vector for INNS transport, and hard substrates installed during the construction phase represent potential new habitat for INNS to colonise in the operation and maintenance phase.
415. The MDS for the Array accounts for up to 17,780 vessel round trips over its 35 year lifecycle, or 508 round trips per year ( Table 8.12   Open ▸ ). There may be up to 31 vessels on site at any one time. As above for the site preparation and construction phase, these vessels provide vectors for the potential introduction of INNS into the habitats within the Array benthic subtidal ecology study area. In addition, the installation of artificial hard substrate on the seabed and in the water column during the construction phase could provide new habitat for INNS to colonise throughout the lifecycle of the Array. In the absence of a MDS for Morven Offshore Wind Farm, even if it is assumed that it will have a larger footprint, the cumulative magnitude of impact is still not expected to represent a material additional impact to that defined for the assessment of the Array alone (section 8.11). Further, vessel movements associated with the Morven Offshore Wind Farm and the Array may follow similar routes and vessels associated with the Array may pass through the Morven Offshore Wind Farm. However, vessels associated with both will be required to comply with an INNSMP, which includes the IMO ballast water management guidelines, which help reduce the risk of potential introduction and spread of INNS as far as practicable ( Table 8.17   Open ▸ ).
416. As above for the site preparation and construction phase, many of the vessels are likely to come to and from the vicinity of the Array benthic subtidal ecology study area. Therefore, the potential for introduction of INNS from outside this region is reduced.  
417. Overall, for all IEFs, the cumulative impact is predicted to be of local spatial extent, long term duration over the operation and maintenance phase, intermittent (in terms of invasions), and of low reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the receptor

418. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.21   Open ▸ and paragraphs 188 to 191).
419. Overall, all IEFs are deemed to be of high vulnerability, low recoverability, and regional to national value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

420. Overall, for all IEFs, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the effect will, therefore, be of minor to moderate significance. Given the low footprint of hard substrates to be installed in the Tier 2 projects that could be colonised by INNS, and the designed in mitigation measure of an INNSMP, the cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

421. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.

                        Tier 3

                        Construction phase

Magnitude of impact

422. In addition to the Tier 1 and Tier 2 projects, there were six Tier 3 projects identified with potential for cumulative effects associated with this impact:

• Morven Offshore Export Cable Corridor(s);
• Bellrock Offshore Wind Farm;
• Bowdun Offshore Wind Farm;
• Campion Offshore Wind Farm;
• Eastern Green Link 3; and
• Eastern Green Link 4.

423. As these are Tier 3 projects, there are no Scoping Reports or EIA documents available in the public domain. Therefore, there is no information available on the impact that these Tier 3 projects will have on benthic subtidal ecology. Vessel activities associated with Bellrock, Bowdun, and Campion Offshore Wind Farms are likely to be similar to those of the Array, and those associated with the Morven Offshore Export Cable Corridor(s) and Eastern Green Link 3 and 4 are likely to be similar to those discussed above for the Eastern Green Link 2 in the Tier 1 assessment (paragraphs 386 to 393). Given the higher number of wind turbines and energy generation capacity of the Array in comparison to the Bellrock, Bowdun, and Campion Offshore Wind Farms ( Table 8.22   Open ▸ ) it is likely that the maximum area of hard substrates installed (that could be colonised by INNS) will be higher for the Array (19.27 km2 on the seabed and an unquantifiable area in the water column; Table 8.12   Open ▸ ). Further, as Bellrock and Campion Offshore Wind Farms are floating projects, the towing of wind turbines may also represent an additional pathway for INNS, as per the Array. However, further information on this is unavailable at the time of writing. The cumulative magnitude of impact of the Tier 3 assessment is therefore not expected to represent a material additional impact to that defined for the assessment of the Array alone (section 8.11).
424. As above for the Tier 1 assessment, many of the vessels are likely to come to and from the vicinity of the Array benthic subtidal ecology study area. Therefore, the potential for introduction of INNS from outside this region is reduced.  
425. As above for the Tier 1 assessment, the implementation of an INNSMP is a designed in measure which aims to manage and reduce the potential risk of introduction and spread of INNS as far as reasonably practicable ( Table 8.17   Open ▸ ). All vessels associated with the Tier 2 assessment will be required to comply with the IMO ballast water management guidelines, which will help reduce the risk of potential introduction and spread of INNS as far as practicable.
426. Overall, for all IEFs, the cumulative impact is predicted to be of local spatial extent, medium term duration over the site preparation and construction phase, intermittent (in terms of invasions), and of low reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the receptor

427. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.21   Open ▸ and paragraphs 188 to 191).
428. Overall, all IEFs are deemed to be of high vulnerability, low recoverability, and regional to national value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

429. Overall, for all IEFs, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the effect will, therefore, be of minor to moderate significance. Given the low footprint of hard substrates to be installed in the Tier 3 projects that could be colonised by INNS, and the designed in mitigation measure of an INNSMP, the cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

430. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.

Operation and maintenance phase

Magnitude of impact

431. In addition to the Tier 1 and Tier 2 projects, there were six Tier 3 projects identified with potential for cumulative effects associated with this impact:

• Morven Offshore Export Cable Corridor(s);
• Bellrock Offshore Wind Farm;
• Bowdun Offshore Wind Farm;
• Campion Offshore Wind Farm;
• Eastern Green Link 3; and
• Eastern Green Link 4.

432. As these are Tier 3 projects, there are no Scoping Reports or EIA documents available in the public domain. Therefore, there is no information available on the impact that these Tier 3 projects will have on benthic subtidal ecology. Vessel activities associated with Bellrock, Bowdun, and Campion Offshore Wind Farms are likely to be similar to those of the Array, and those associated with the Morven Offshore Export Cable Corridor(s) and Eastern Green Link 3 and 4 are likely to be similar to those discussed above for the Eastern Green Link 2. Given the higher number of wind turbines and energy generation capacity of the Array in comparison to the Bellrock, Bowdun, and Campion Offshore Wind Farms ( Table 8.22   Open ▸ ) it is likely that the maximum area of hard substrates (that could be colonised by INNS) will be higher for the Array (19.27 km2; Table 8.12   Open ▸ ). The cumulative magnitude of impact of the Tier 3 assessment is therefore not expected to represent a material additional impact to that defined for the assessment of the Array alone (section 8.11).
433. As above for the site preparation and construction phase, many of the vessels are likely to come to and from the vicinity of the Array benthic subtidal ecology study area. Therefore, the potential for introduction of INNS from outside this region is reduced.
434. As above for the site preparation and construction phase, the implementation of an INNSMP is a designed in measure which aims to manage and reduce the potential risk of introduction and spread of INNS as far as reasonably practicable ( Table 8.17   Open ▸ ). All vessels associated with the Tier 3 assessment will be required to comply with the IMO ballast water management guidelines, which will help reduce the risk of potential introduction and spread of INNS as far as practicable.
435. Overall, for all IEFs, the cumulative impact is predicted to be of local spatial extent, long term duration over the operation and maintenance phase, intermittent (in terms of invasions), and of low reversibility. It is predicted that the impact will affect the receptors directly. The magnitude is therefore considered to be low.

Sensitivity of the receptor

436. The sensitivities of the benthic subtidal ecology IEFs are as previously described above for the assessment of the Array alone (see Table 8.21   Open ▸ and paragraphs 188 to 191).
437. Overall, all IEFs are deemed to be of high vulnerability, low recoverability, and regional to national value. The sensitivities of the receptors are, therefore, considered to be high.

Significance of effect

438. Overall, for all IEFs, the cumulative magnitude of the impact is deemed to be low, and the sensitivities of the receptors are considered to be high. As per Table 8.16   Open ▸ , the effect will, therefore, be of minor to moderate significance. Given the low footprint of hard substrates to be installed in the Tier 3 projects that could be colonised by INNS, and the designed in mitigation measure of an INNSMP, the cumulative effect will, therefore, be of minor adverse significance, which is not significant in EIA terms.

Further mitigation and residual effect

439. No benthic subtidal ecology mitigation is considered necessary because the likely cumulative effect in the absence of further mitigation (beyond the designed in measures outlined in section 8.10) is not significant in EIA terms.