Jean-Marc Brignon
email: jean-marc.brignon@ineris.fr.

Morgane Lejart

Maëlle Nexer

Sylvain Michel

Alan Quentric

Léa Thiebaud

A risk-based method to prioritize cumulative impacts assessment on marine biodiversity and research policy for offshore wind farms in France

Keywords: Marine ecosystem, cumulative impact assessment, offshore wind energy, risk-based approach, prioritization, anthropogenic pressures, impact pathways

This study developed the "ECUME" risk-based approach to identify and prioritize critical impact pathways to be considered in cumulative impact assessment of offshore windfarms, and for future research. The prioritization framework has been tested on two offshore windfarms projects located in the French part of the English Channel off the coast of Normandy, those of Fécamp and Courseulles-sur-Mer. The approach is based on a complete inventory of impact pathways, prioritizing those for which an impact assessment will be carried out. The aim was to avoid a "quantification bias" and elaborate a systemic vision. The novelty of the study is to apply a combination of expert judgement, consensus building, and a scoring system, to prioritize the pairs of pressures and receptors of the marine environment to work on. The scoring system is based on the ecological importance of receptors, the degree of knowledge on the effect of a pressure on a receptor and the sensitivity of each receptor to pressures. Priorities for research were also determined during the same process. Bringing together a large set of specialized marine environnement scientists, the initial challenge was to build a common vocabulary, and a shared understanding of the risk-based prioritization approach. This required significant time and effort but secured foundations for further work. This study confirms the increasingly shared view that adopting a risk-based approach considering adverse effects on receptors is an efficient way to assess cumulative impacts, to focus on critical impact pathways, and manage the scientific complexity and the significant uncertainties.

• We prioritize issues in cumulative impact assessment of offshore windfarms • Prioritization combines risk-based expert judgement and a scoring system • It is also used to identify priority research areas for the future • It was tested on two French offshore windfarm projects • Such a risk-based approach allows to manage scientific complexity and uncertainties

INTRODUCTION

GENERAL BACKGROUND

Marine ecosystems are subject to pressures (e.g. seafloor habitats modification or destruction, noise, emission of light, chemical pollution, mortality…) generated by human activities (fishing, dredging, aggregates extraction, marine energies,…). Among these activities, multiple offshore wind farms (OWF) projects are increasingly being implemented in different marine regions (GWEC, 2019). In northern Europe, the North Sea is seeing a high and growing density of wind farms. In France, no OWF is in operation currently, but several are under construction or already planned by the government, with the national objective of an installed capacity of 2,4 GW in 2023 and around 5 GW in 2028 [START_REF] Mte | Stratégie française pour l'énergie et le Climat[END_REF]. In 2018, The French Ministry for Ecology considering that this situation required a cumulative impacts assessment of these projects on marine and coastal ecosystems, established the "ECUME" scientific working group (WG) (for "Effets CUMulés des projets Eoliens en Mer" : Cumulative effects of offshore wind projects). The ECUME WG has been tasked with developing a methodological approach to assess the cumulative impacts of French and relevant foreign projects, and to demonstrate its feasibility on two OWF projects located off the coast of Normandy, those of Fécamp and Courseulles-sur-Mer (Eastern Channel) (Figure 1). The Cumulative Impacts Assessment (CIA) should also include other anthropogenic activities that will increase the pressures from OWFs at the local or wider scale. The objective of this paper is to describe a method to identify and prioritize the pressures and impact pathways that should be considered in the development of the ECUME CIA method, and its application to the eastern English Channel and southern North Sea. The paper also provides information on the organisation and general methodological approach of the forthcoming development of the CIA itself.

BRIEF OUTLOOK OF SCIENTIFIC APPROACHES FOR MARINE CUMULATIVE IMPACTS

With the growth of human activities at sea, intense research focuses on CIA on marine ecosystems, building on previous broader knowledge and practice of CIA in other fields. CIA has long been considered as part of Environmental Impact Assessment (EIA) (European Communities, 1999), and should as a first requirement follow EIA principles. Several published guidance from both the public and private sectors address the cumulative impacts (European Communities, 1999;IFC, 2013), several being specific to the marine environment (European Commission, 2013;Renewables UK, 2013;[START_REF] Mtes | Évaluation environnementale[END_REF]. The European Marine Strategy Framework Directive (MSFD) refers to cumulative effects but restricted to the assessment of ecological state of the marine environment. In the scientific literature, (Willsteed E. et al., 2017;[START_REF] Borja | Overview of Integrative Assessment of Marine Systems: The Ecosystem Approach in Practice[END_REF]Duinker P. N. et al., 2012;Duinker P. N. & Greig L. A., 2006) underline the importance of following a standardised and rigorous impact assessment method, with transparent and careful formulation of objectives and scenarios definition. Because the outcome of assessments are scale and scope dependant [START_REF] Lindeboom | Offshore wind offshore windfarm monitoring programmes, lessons learned and recommendations for the future[END_REF]Rijkswaterstaat, 2019) a fundamental underlying principle of CIA is the need for clarity on these geographical scales and temporal scope. The "before-after-controlimpact" (BACI) method to monitor the effects of OWFs considers that scenarios representing the marine environment respectively with and without the offshore project should be compared [START_REF] Methratta | Monitoring fisheries resources at offshore wind farms: BACI vs. BAG designs[END_REF]. There are many variations in the denominations and concepts of CIA frameworks used in the marine environment (Tamis J.E. et al 2016). However, it is becoming a shared view at a theoretical level (Judd A.D. et al., 2015;[START_REF] Hodgson | Moving Beyond Silos in Cumulative Effects Assessment[END_REF] and in practical applications [START_REF] Singh | Mapping cumulative impacts to coastal ecosystem services in British Columbia[END_REF]Verling E. et al., 2021), that given the high uncertainties in the impact causality chains, it is advisable to adopt a risk-based (rather than fully deterministic) approach in marine CIA. Risk-based assessment, that relies on describing the probability of adverse effects, is useful when high uncertainty and lack of knowledge make predictions difficult and poorly reliable and informative. It also helps in such contexts to design preventive action before projects, and adaptative surveillance and mitigation of impacts during the life of projects.

In the ECUME WG, such a risk-based approach will be used for CIA and has already been applied in the work reported here to prioritize impact pathways and research priorities. The need to consider all stressors and all potentially impacted receptors (Willsteed E.A. et al., 2018;[START_REF] Borja | Overview of Integrative Assessment of Marine Systems: The Ecosystem Approach in Practice[END_REF] increases complexity and uncertainties (with associated data and scientific challenges) (Piet G.J. et al., 2015;[START_REF] Dannheim | Benthic effects of offshore renewables: identification of knowledge gaps and urgently needed research[END_REF]. Therefore, prioritization methods to decrease the number of pressures, habitats and species (hence impact pathways) to be assessed has already been used for OWF, especially applied to seabirds [START_REF] Bradbury | Mapping Seabird Sensitivity to Offshore Wind Farms[END_REF][START_REF] Furness | Assessing vulnerability of marine bird populations to offshore wind farms[END_REF][START_REF] Desholm | Avian sensitivity to mortality: Prioritizing migratory bird species for assessment at proposed wind farms[END_REF][START_REF] Garthe | Scaling possible adverse effects of marine wind farms on seabirds: developing and applying a vulnerability index[END_REF]. A more comprehensive prioritization process is described in (Tamis J.E. et al., 2016) and our work builds on this latter approach, also adding an explicit scoring system to the expert judgement. We apply this framework to identify priority pressures and receptors for the development of the ECUME CIA, and also to prioritize the main scientific knowledge gaps that need to be addressed in the future course of the ECUME WG and at international level in the North Sea region. Section 2 of this article describes the general CIA approach in ECUME (2.1 and 2.2) and in more detail the risk-based prioritization of pressures and receptors for developing the CIA framework (2.3) and for future research (2.4). Section 3 presents and discusses results from the risk-based prioritization applied to the test area in the English Channel, then discusses its limits and possible improvements.

MATERIALS AND METHODS

PROJECT ORGANIZATION AND INTEGRATION OF SCIENTIFIC EXPERTISE

The ECUME WG involves several types of actors, the role of each being explained in this section and in the organization chart (Figure 2). Public administration is involved in: i) in setting the objectives and in the validation of the deliverables of the WG to ensure its compliance with national regulations and guidance, and ii) financing and organising the technical and scientific support. Several French public or semi-public research institutes and agencies (Ineris, France Energies Marines, Cerema, and OFB) oversee the technical work, and the scientific management of experts in the WG. Around 30 scientific experts participating directly in ECUME bring knowledge of the marine ecosystem and their understanding of uncertainties in how these ecosystems are impacted by anthropogenic activities. They are academics or public researchers and were selected as specialists of each of the components of the marine ecosystem (birds, mammals, fish, benthic communities, etc.) and of pressures (noise, chemical pollution, modifications of physical habitats, etc.). Moreover, they are connected to their wider scientific communities who hence indirectly contribute to the ECUME WG. The scientific expertise is key in the WG and covers as far as possible all aspects of the marine environment, including the functioning of the whole ecosystem. As underlined by [START_REF] Lindeboom | Offshore wind offshore windfarm monitoring programmes, lessons learned and recommendations for the future[END_REF]Tamis J.E. et al., 2016;[START_REF] Borja | Overview of Integrative Assessment of Marine Systems: The Ecosystem Approach in Practice[END_REF] it is crucial to add ecosystem modelling and expertise to this framework to represent indirect / synergistic and trophic effects. Scientific experts are managed to ensure their engagement, and therefore strengthen the scientific quality of the results. Inclusion of expertise was organized through a participatory approach, with regular seminars held to build consensus regarding scientific issues. Finally, the ECUME WG integrates "socio-professional observers" from stakeholder organisations representing professional activities of the marine environment: National Fisheries Committee (CNPMEM), Federation of Wind Energy and the Renewable Energies Union (FEE and SER), electricity network manager (RTE). Stakeholders from environmental NGOs (France Nature Environnement, the French committee of IUCN) are also present at important milestones.

CUMULATIVE IMPACT ASSESSMENT FRAMEWORK

Cumulative impacts relate to the multiplicity of human activities and projects that generate various pressures that accumulate and affect receptors in the marine ecosystem and this ecosystem as a whole (in a linear or non-linear way, at the same or distinct periods, at the same or distinct locations, through multiple direct and indirect pathways with synergistic and antagonistic effects).

To address this complexity, the ECUME WG decided to follow and adapt to the OWF context the EIA method and formulate it in a risk-based setting (Figure 3). The ECUME WG reviewed the literature on EIA methods, and international experience of their application. A scientific seminar concluded that the best approach was, in the context of limited scientific understanding of impacts, to combine "impact pathways", risk-based approaches, and ecosystem modelling. The standard impact assessment methodology common to most frameworks can be summarized in five steps: Goal and Scope definition, Preliminary Analysis, Scenarios definition (Baseline, Project, Alternatives), Scenarios Impact Assessment, Interpretation. Accordingly, ECUME WG decided to base its methodology on this comparative assessment framework.

The paper concentrates on the "Objective and Scope" and "Preliminary Analysis" steps, that is the inventory and prioritization of the objects subject to the CIA. This work is based on the notion of "impact chain" or "impact pathway", connecting activities to receptors through pressures. It has commonly been used in health and environmental assessment and in the context of CIA in the marine environment [START_REF] Bailey | Assessing environmental impacts of offshore wind farms: lessons learned and recommendations for the future[END_REF][START_REF] Robinson | Towards delivering ecosystem-based marine management: The ODEMM Approach[END_REF][START_REF] Menegon | A modeling framework for MSP-oriented cumulative effects assessment[END_REF][START_REF] Dannheim | Benthic effects of offshore renewables: identification of knowledge gaps and urgently needed research[END_REF]. Identifying impact chains is a first step to understand the potential impacts, and enables the assessment of the response of receptors to changes in activities, all along the DAPSI(W)R(M)framework (Driver -Activities -Pressure -State -Impact -(Welfare) -Response-(Measures)), also currently used for marine ecosystem assessment (Smith J.C. et al., 2016;[START_REF] Elliott | And DPSIR begat DAPSI(W)R(M)!" -A unifying framework for marine environmental management[END_REF]Rijkswaterstaat, 2019). There are few available models to predict these responses, especially for some environmental compartments (for example, few models exist concerning the benthic compartment). To avoid fundamental biases if focussing only on impacts chains for which models are available, the ECUME WG started with an exhaustive inventory of impact pathways, prioritizing those for which an impact assessment would be carried out, using modelling if available, or any other quantitative and qualitative method scientifically validated by ECUME experts (exposure or risk indicators maps, expert judgement). The aim is to build a pragmatic, manageable but holistic vision of the risks incurred by the marine environment and to avoid the "quantification bias". However, impact pathways approach alone cannot capture cumulative impacts from ecosystem interactions and dynamics effects. A systemic vision will further be built with ecosystem modelling, including physical and intertidal effects modelling where relevant, and the development of indicators of state change, but this is beyond the scope of the present paper.

The ECUME WG intends to apply for testing purposes the methodology outlined in this section to two OWFs projects located off the coast of Normandy, those of Fécamp and Courseulles-sur-Mer (Figure 1), and surrounding OWFs in the same marine region, that will be considered relevant in terms of cumulative impacts, in particular for the mobile megafauna.

INVENTORY AND SELECTION OF PRIORITY PRESSURES AND RECEPTORS

This section describes the inventory and prioritization of impact pathways of the "Objective and Scope" and "Preliminary Analysis" stages in Figure 3. The ECUME WG carried out an inventory of all activities related to OWFs and the pressures they generate. These activities were identified for each stage of their lifecycle (construction, operation, decommissioning). The list of anthropogenic pressures is based on the MSFD typology, adapted following the works from (La [START_REF] Rivière | Méthodologie pour l'évaluation de la sensibilité des habitats benthiques aux pressions anthropiques[END_REF] for physical pressures on benthic habitats and (Quemmerais F. et al, 2020) for other physical, chemical and biological pressures. The list of biological receptors (habitat types, individual species, …) potentially impacted by pressures from OWF was built from the 2 OWFs environmental impact studies and complemented during experts workshops. Their high number would give rise to an unmanageable number of more than 5 000 impact chains. Therefore, it was decided to carry out an initial screening and grouping

Risk Analysis

Cumulative Impact / Risk Assessment Cycle Acceptability of policy step based on expert scientific knowledge before applying a more structured prioritization method on a still large but manageable starting list. This process was carried out in four steps (Figure 4): -inventory of pressures and receptors initial screening of relevant receptors, activities and relevant pressure/receptor pairs systematic ranking of all relevant pressure/receptor pairs by a scoring system underpinned by expert scientific knowledge, described hereafter in detail (see "Systematic ranking of all pairs of pressures and receptors") -selection of final most relevant priorities by collective and transdisciplinary expert judgement during workshops .

Initial screening and grouping of most relevant activities and receptors

The screening was performed to retain only pressures generated within an OWF project, but only in normal conditions (i.e. excluding all kinds of accidental events, such as leakages, ship collisions, unforeseen maintenance operations, etc.). Some pressures that might be generated by OWFs but to a negligible extent compared to other sources of this pressure, in the eastern English Channel and southern North Sea region, were discarded during this screening, such as water temperature increase. All types of fixed foundations OWF were considered (monopiles, jackets and gravitybased structures), but not floating OWF as this technology is only emerging worldwide and will not be implemented commercially in France before 2027. The pressures associated with preconstruction activities (environmental, ecological and geophysical surveys, seafloor sampling and drilling) were considered as part of the construction phase. The complete list of receptors included prior to screening around 452 species and habitats and was based on the full lists of habitats and species presented in the regulatory impact assessment reports of the Fécamp and Courseulles-sur-Mer windfarms projects. The species and habitats have been classified in four groups:

benthic habitats and communities (initial number of 300 species) -ichthyofauna and planktonic communities (initial number of 101 species) -marine mammals and turtles (initial number of 9 species) -flying fauna (initial number of 36 bird species and 6 bat species)

Preliminary Analysis Prioritization

Inventory of pressures from OWFs and of receptors

Screening and grouping of pressures and of receptors

Criteria scoring by experts of each Pressure / Receptor couples (Sensitivity / Knowledge / Conservation status)

Collective Expert elicitation of priorities using multicriteria ranking -For cumulative impact studies -For longer term research

For each group, the following specific scientific literature and rationale were used by ECUME experts: For benthic habitats and communities, the number of receptors was reduced by grouping habitat types to the EUNIS 5 level, and to only consider the subtidal habitats. For ichthyofauna, ECUME experts grouped the species by categories according to their habitats and phylogenetic supergroups (i.e. Actinopterigians, Elasmobranches and Cephalopods). Habitats and species were classified according to their position in the water column (benthic, demersal, pelagic), dependence to freshwaters (amphihaline or not), type of seabed (rocky, muddy, sandy, mixed) and location (on the shore, offshore). Trophic position of species was also considered, in case trophic models would be used for impact assessment. For instance, rays were distinguished from other benthic fishes. For marine mammals and sea turtles, experts selected the most common species based on their knowledge of observation data in the study area. They selected turtles that can be, even at low numbers, regularly observed in the English Channel / North Sea area, but not those that are only occasionally observed (in exceptional circumstances for only one or a few individuals), which led to discard the green turtle, based on (Nivière M. et al., 2018). The harbour porpoise is the most common marine mammal species in the study area. Bottlenose dolphins, grey seals and harbour seals are also frequently observed. These species were then considered separately from cetaceans and from pinnipeds. Experts identified "indicator" bird species representing the different families of seabirds relevant and most at risk for the area. The collision and displacement risk indicators provided by (Furness S. et al., 2013) and [START_REF] Bradbury | Mapping Seabird Sensitivity to Offshore Wind Farms[END_REF] were used as an additional guideline. These indicators are based on observations in the British part of the North Sea which is close to but distinct from our study area, and these studies partly rely on extrapolated data. Furthermore, the indicators are estimated for wind turbines 150m high, while those for French projects will reach 180 to 220 m, and they do not consider the differences between sites, colonies or populations, nor differences between nesting and wintering periods, and they cannot be used for migration periods. Experts were therefore the main source of information to design a species list adapted to the ECUME context. A category of passerine birds was added to take account of terrestrial birds which are exposed to collision risk with OWFs during their migrations. A summary of structured groupings made can be found in first columns in Tables 2 to 5.

Systematic ranking of all pairs of pressures and receptors

Our approach relies on identifying the major risks of adverse and cumulative effects, as advocated by (Rijkswaterstaat, 2019). We focus on species that are the most sensitive, most at stake for the ecosystem, and for which at least a qualitative assessment (possibly based on expert judgement) of cumulative impacts is feasible with an acceptable level of uncertainty. It was agreed by experts that the acceptable level of uncertainty was defined on a case-by-case basis through discussion, based on their knowledge of the amount and quality of scientific evidence available regarding the sensitivity of the receptor to the pressure. This prioritization will also allow to identify pressure-receptors pairs for which it is currently not possible to assess the impacts due to too severe gaps in scientific knowledge, or too high uncertainties. The aim of the ECUME WG is in this respect to inform on priorities for scientific research to improve CIAs in the future. Each pressure-receptor pair was quoted based on the following scoring system:

-A first score (1 to 10), reflects the level of sensitivity (S) of the receptor to the pressure, within a realistic range of its intensity in the real-life marine environment but regardless of its actual value (the actual value of pressures is taken into account during the impact assessment phase). This score includes an appreciation of how severe the consequence of exposure might be at individual level for the receptor, for instance whether survival can be at stake, -A second score (1 to 10) reflects the level of scientific knowledge (K) on the interaction between the pressure and the receptor. This score is an appreciation by experts regarding how much the pressure-receptor relationship is proven (in terms of the amount and quality of available scientific evidence) and can be at least qualitatively assessed meaningfully (so that the results are reliable enough to modify the design or even reconsider the OWF projects for instance). -A third score (1 to 10) representing the conservation status (St) of the receptor. This St score is inspired by the "focal" species concept (i.e. important from either the perspective of ecosystem conservation or ecosystem services) advocated in several impact assessments of human activities on marine ecosystems [START_REF] Link | Translating ecosystem indicators into decision criteria[END_REF]Zacharias M.A. et al., 2001). The St score also includes qualitative consideration of the socio-economic importance of the species (economic and/or patrimonial value). The St-scores were attributed transcribing on a numerical scale previous expert evaluation carried out within the framework of the implementation of the MSFD and the MSPD1 in the marine region of concern (MTES and AFB, 2019). These evaluations included the species conservation statutes at the French national or European level published by the IUCN (IUCN French committee, 2013, 2015, 2016and 2017). When different scores were attributed to different sectors of the East Channel and North Sea subregion, the maximum score was retained.

These score need to be balanced against each other, and therefore they are combined in a multiplicative way (S x K x St), so that the pressure/receptor pairs being subject to a more critical (S and St) and more scientifically established (K) potential adverse effect are in priority included further in the CIA. The precautionary principle was applied throughout the process by the ECUME scientific team and experts, using a "realistic worst case" approach for setting the values for the scores, similar to the one adopted in the Dutch KEC framework for cumulative effects (Rijkswaterstaat, 2019). In practice the realistic worst case approach consisted for example, if an interval of sensitivity scores were considered possible by the expert group, to not retain the absolute maximum sensitivity possible according to a single expert (that would be "worst case") but a value representing the maximum that the whole group agreed on. The numerical values of K and S scores where first proposed by the ECUME project team, then consolidated by the experts during a full one-day seminar. The experts worked first in subgroups for each environmental compartment (Benthic habitats and communities, Ichthyofauna and plankton, Marine mammals and turtles, Birds and chiropters), and then shared their work to improve the consistency of quotations between subgroups.

To guide experts involvement, we followed and adapted the general features of the "Investigate," "Discuss," "Estimate" and "Aggregate" IDEA procedure for expert elicitation [START_REF] Hemming | Preparing and implementing a structured expert elicitation using the IDEA protocol[END_REF]. The pre-elicitation phase was fully carried out, but in some cases the personal investigation ahead of expert meetings was prepared by only some of them, leading to more importance put on the discussion and post-elicitation phase during expert workshops. There were no predefined criteria to guide experts in using the 1 to 10 scale. Experts were invited ahead of workshop discussions to prepare their individual scoring based on literature and their own judgement. Each expert own recourse to literature and own judgement was not precisely traced, and variation between experts in terms of their own working methodology can be a source of uncertainty and lack of robustness in the whole prioritization.

Selection of final priorities by experts

Based on the quotations by experts, we prepared the rankings of all pairs of pressures and related receptors, grouping them into the four ecological compartments (benthic habitats and communities, ichthyofauna and planktonic communities, marine mammals and turtles, and flying fauna). Prior to presentation to experts, the team merged certain pairs that obviously would be assessed together, and also suggested to discard some pairs for which it was evident that the current unavailability of data, or time and resources constraints of the ECUME WG would make any assessment impossible.

However, such discarded pairs would automatically be identified as potential scientific research priorities. Examples of such discarded pairs (but systematically considered for being a research priority) are, for each compartment, the following : Introduction of non-native species for all benthic communities species, Underwater collision for cetaceans, Obstacle to movements, feeding and rest for amphialine fishes, and Disturbance in the aerial environment by human presence for ducks (scoters). We also proposed to cut the list at a point where all remaining pairs appeared to not cause any significant impact.

All lists and suggestions (groupings and discarding) were thoroughly reviewed and discussed by the scientific experts during a second one-day seminar, again with work in subgroups followed by harmonization between groups results. Experts were free to integrate pairs that they felt, independently of their previous quotations and of rankings, would finally be important for the CIA.

It was made clear that a low Knowledge score should not necessarily lead to the exclusion of pressure/receptor pairs, and that final collective expert judgment had to prevail over the systematic ranking obtained through the scoring system.

Even if an ecosystemic approach will also be implemented in ECUME at a later stage, experts were invited to take already into account during this exercise the possible cumulative and combination effects (synergistic or antagonistic) between pressures, and the interactions between receptors.

Overall, the experts found the prioritization quite helpful in keeping the scientific discussion and the exercise manageable. Discussions during the seminar lead to some additional groupings, and some significant changes to the proposed pre-prioritization.

INVENTORY AND SELECTION OF PRIORITY RESEARCH AREAS

A second aim of the ECUME WG is to prepare a research agenda for the CIA of OWFs on the marine environment. The above process was also used to identify research priorities with the group of experts. The same scores were combined in a different way (S x (1/K) x St), so that the pairs reflecting a more critical but less scientifically established issue clearly move up in the research priority hierarchy, to be eventually included in CIAs as soon as acquired knowledge allows to confirm or not the potential concern. A preliminary list of research priorities based on these scores was first analysed by the project team. Finally, this list was further discussed during a third workshop with experts to establish 4 to 6 research priorities by component of the marine ecosystem. .

RESULTS AND DISCUSSION

In this section we describe and discuss results from the prioritization of impact pathways, applying the methodology outlined in section 2.3.

INITIAL SCREENING OF MOST RELEVANT RECEPTORS

The complete initial list of receptors for the Courseulles-sur-Mer and Fécamp wind farms included a total of 452 species that was finally reduced to 41 species or groups of species and habitats, for both OWFs. A challenge was to ensure the same understanding among different experts of when the presence of a habitat or a species in the study area was significant enough to justify its inclusion. Some experts might unintentionally tend to focus more on the ecosystem component they are specialized in and consider it should be integrated in the scoping phase, which could bias the selection process. This issue was resolved by strong adhesion of experts to the objectives and consensus building, to finally agree on priority species and habitats (Table 1). This list contains 6 benthic habitats types (EUNIS level 5) which are the most prevalent ones in the subtidal part of the study area. Ichtyofauna is represented through 12 groups of species, divided into 3 groups for benthic rays, 1 group for benthic cephalopods and 8 groups for Actinopterigians (i.e. bonny fish): 1 diadromous, 2 benthic, 3 demersal, 1 bentho-pelagic and 1 pelagic fish groups. Two receptors are also introduced to describe the pelagic communities: phytoplankton (i.e. micro-algae) and zooplankton (including ichtyofauna larvae). The marine mammals species are much less numerous than fish species, thus individual species were retained, focusing on the most common species in the study area: 2 small cetaceans species and 2 pinnipeds species. Marine turtles are considered by selecting the 2 species which are occasionally found in the English Channel. Seabirds are considered through 11 species which are representative of wider species groups. Scoters are retained to represent the group of sea ducks, Eurasian curlew to represent shorebirds, and Passerines to represent all terrestrial migratory birds which may cross seasonally the study area. Ultimately, chiropterans species are synthetized by selecting 6 species which are considered by the experts as potentially present at sea in the study area, either during their migratory flights or for feeding during their reproduction period.

PRIORITIZATION OF MAJOR PRESSURES AND RECEPTORS

Relevant pressures for impact pathways related to OWFs where first identified through building a correspondence matrix between activities related to OWFs lifecycle, and pressures. 18 relevant pressures were identified during the construction phase, 16 pressures during the exploitation phase and 13 during the decommissioning phase. All the pressures potentially generated during decommissioning are also generated during construction, as the nature of activities as similar for these two phases.

Table 2:"sensitivity index" (S) for each pair of pressure (columns) and receptor (lines).

This matrix was used to quote relations between each pressure and each receptor in terms of sensitivity of the receptor to the pressure, from 1 to 10, 10 corresponding to a maximum level across all the pressures and receptors preselected in ECUME (Table 2). Blank cells correspond to cases in which no significant potential relationship exists between the pressure and the receptor (in the context of OWFs). For instance, the sensitivity of benthic habitats to "physical habitat loss" was scored 10, as this pressure produces a total and permanent loss of any marine habitat. Conversely, the sensitivity of plankton communities to the "introduction of individuals genetically different from local populations" was set to 1, as the interaction appears to have potential low

1 1 1 1 1 1 1 1 1 1 1 1 2 5 Benthic-loose rays -offshore 1 1 1 1 1 Benthic-loose rays -coastal 1 0 1 0 1 0 5 5 1 1 1 1 1 1 1 1 1 1 5 5 Cephalopods Coastal benthics -soft bottoms 1 1 1 1 1 1 1 1 1 1 1 5 1 2 Amphihalins 1 1 1 1 1 5 1 5 1 1 1 1 1 1 1 0 Benthic -soft bottoms 1 0 1 0 1 0 1 5 1 1 3 1 1 1 1 1 1 5 1 Coastal benthic -rocky bottoms 1 1 1 1 1 1 1 1 1 1 1 1 1 5 1 2 1 Bentho-pelagic -sandy bottoms 5 5 1 0 1 1 1 5 5 5 1 1 1 1 5 1 2 1 0 Demersals -movable funds 7 5 1 0 1 5 1 1 3 3 1 1 1 1 5 1 5 1 0 Coastal demersals -mixed bottoms 3 1 5 1 1 1 1 1 3 1 1 1 1 1 2 1 0 Demersals -mixed funds 3 1 1 1 1 1 1 1 3 1 1 1 1 2 1 0 Pelagic 1 1 1 1 5 5 5

Marine reptiles

Sea turtles

Benthic habitats and communities

Marine mammals

Pinnipeds

Cetaceans

Bats

Pelagic communities

Pisces

Elasmobranchs (rays and sharks)

Actinopterygii

Birds

-13 / 27 -adverse effect. Relations between pressures and receptors were also rated in terms of "Knowledge" of the previous level of sensitivity, again from 1 to 10 (Table 3).

Table 3: "knowledge index" (K) for each pair composed of pressure (columns) and receptor (lines).

Another matrix was used to record "conservation status" (St), established according to the procedure described in section 2 (Table 4).

Marine reptiles

Sea turtles

Benthic habitats and communities

Marine mammals

Pinnipeds Cetaceans

Bats

Pelagic communities

Pisces

Elasmobranchs (rays and sharks)

Actinopterygii

Birds

-14 / 27 - After application of the prioritization procedure outlined in section 2.3, the final scoring of pairs of pressures and receptors was the following (Table 5, in which higher scores denote higher priority). Tables 6 to 8 summarize the reduced number of final priorities after grouping and selection by experts, for each ecological compartment. For Ichtyofauna, experts faced difficulty to establish priorities because of the critical lack of knowledge regarding the sensitivity of species to pressures. The priority for this compartment is to acquire more knowledge regarding sensitivity of species. Therefore, this compartment has not been addressed in terms of CIA studies to be launched but in terms of setting research priorities (see section 3.1) Table 5: "cumulative impact priority index" (P) for each pair of pressure (columns) and receptor (lines).

For benthic habitats and communities (Table 6), the experts concluded that all six selected habitat types should be considered together, and they only prioritized the pressures which affect them as a whole.

Benthic habitats and communities

Bats

Pelagic communities

Pisces

Elasmobranchs (rays and sharks)

Actinopterygii

Birds

Marine reptiles

Sea turtles

Marine mammals

Pinnipeds

Cetaceans

This study developed the "ECUME" risk-based approach to prioritize impact pathways (i.e. activity pressure -receptor chains) that should be considered in CIA of OWFs and identify critical research needs. The prioritization framework has been tested on two OWF projects located in the French part of the English Channel. A complete inventory of pressure-receptor pairs was carried out, followed by their prioritization, using a combination of expert judgement, consensus building, and a scoring system. The scoring system was based on the ecological importance of receptors, degree of knowledge on the effect a pressure on a receptor and the sensitivity of each receptor to pressures. Priorities for research were also assessed during the same process. Some more general lessons were obtained during this first phase of the ECUME project. First, while gathering a large set of specialized marine biologists and other scientists, an initial difficulty was to build a common vocabulary and a shared understanding of a risk-based approach. This required significant time and effort but enabled to secure the rest of the prioritization and forthcoming work of the ECUME WG. Since collective expertise plays an important role, experts must be prepared ahead of workshops to be able to productively exchange during workshops. Prioritization based on expert judgement allows to deal with scientific uncertainty and lack of knowledge but there is a need to repeat this type of exercise in the same and other areas to check their robustness and improve collectively their conclusions.

Setting priorities for research during the same risk-based process as the one used for impact assessment, was useful not only per se, but also to enhance the engagement of the scientific community, who has an interest in contributing to the elaboration of the scientific agenda in marine science. The scoping phase also demonstrated that an exhaustive identification of pressures, and of their future evolutions, is required for a meaningful assessment of OWFs. A significant challenge ahead is to build future scenarios on all marine anthropogenic activities and pressures. The next stage of the ECUME WG will therefore focus on scenario building, identification of available methods and models, and finally CIA per se. In parallel to CIA, several research projects have been initiated on identified priority research areas. Risk-based approaches are relatively new in marine environment management. But despite the initial cultural and vocabulary difficulties mentioned, this approach was useful to manage the scientific complexity and the uncertainties, and therefore increased the quality of the ongoing CIA, avoiding "paralysis by analysis". The risk-based approach is expected to bring the same added value when the ECUME WG will actually assess the consequences for the marine ecosystems of the several OWF projects under its scope, and therefore contribute to the timely and sustainable development of renewable marine energy.

Figure 1 :

 1 Figure 1: Map of the two OWFs of Fécamp and Courseulles-sur-Mer, and other windfarms in the eastern English Channel and southern North Sea.

Figure 2 :

 2 Figure 2: Organisation and governance of the ECUME WG

Figure 3 :

 3 Figure 3: Impact/Risk Assessment methodology in the context of the ECUME WG

Figure 4 :

 4 Figure 4: The ECUME prioritization process and its relation to the whole CIA methodology

Table 4 :

 4 "regional conservation status index" (St) for each receptor (lines) and for different sectors within the French part of the Eastern Channel and North Sea.

						Ecological stake levels					Ecological issue notes
				Sector 1: South North Sea	Sector 2: Picardy	Sector 3: Coastal river -	Sector 4: Eastern Channel Sector 5: Bay of Seine	Sector 1:	Sector 2:	Sector 3:	Sector 4:	Sector 5:	Middle	Maximum
				and Strait of Pas de	estuaries and the Opal	seino-marine littoral			South	Picardy	Coastal	Eastern	Bay of	facade	Channel-
				Calais	Sea			North Sea	estuaries	river -	Channel	Seine	Channel-	East
		Groups	Species family or habitat type					and Strait of Pas de	and the Opal Sea	seino-marine			East North Sea	facade North Sea
									Calais		littoral
			Coarse sediments with circalittoral gravel (Eunis A5.14)	nd (gravel, gravel)	low (coarse sediment)	low (A5.1)	strong (coarse sediment) medium (A5.1)	5	4	4	8	6	5,4	8
			Spirobranchus triqueter (formerly Pomatoceros triqueter), encrusting barnacles and bryozoans on unstable circalittoral pebbles and gravel (EUNIS A5.141) nd (gravel, gravel) low (coarse sediment) low (A5.1)	strong (coarse sediment) medium (A5.1)	5	4	4	8	6	5,4	8
			Mediomastus fragilis, Lumbrineris spp. and venerid bivalves in coarse sand or circalittoral gravel (EUNIS A5.142) nd (gravel, gravel) low (coarse sediment)	low (A5.1)	strong (coarse sediment) medium (A5.1)	5	4	4	8	6	5,4	8
	Benthic habitats and communities		Branchiostoma lanceolatum in coarse sand-gravelly circalittoral sediment (Eunis A5.145) fort (hydraulic dunes)	fort (hydraulic dunes)	low (A5.1)	strong (coarse sediment) medium (A5.1)	8	8	4	8	6	6,8	8
			Stand of heterogeneous sediments (EUNIS A5.44)	way	way	nd (A5.4)		major (A5.4)	6	6	5	2	10	5,8	10
			Shoals of Ophiides Ophiothrix fragilis (EUNIS A5.445)	strong (medium sands)	strong (fine and medium sands) nd (A5.4)		major (A5.4)	8	8	5	2	10	6,6	10
			Benthic crustaceans	strong	low	strong	way	low	8	3	7	6	4	5,6	8
	Marine mammals	Pinnipeds Cetaceans	Gray seal Seal calf marine Harbor porpoise Bottlenose dolphin	major way strong	strong major strong	way way strong (in winter) low	strong (in winter)	low strong medium (in summer) strong	10 6 8 2	8 10 8 2	6 6 8 4	2 2 8 2	4 8 6 8	6,0 6,4 7,6 3,6	10 10 8 8
	Marine reptiles	Sea turtles	Leatherback turtle Dermochelys coriacea loggerhead turtle Caretta caretta						2 2	2 2	2 2	2 2	2 2	2,0 2,0	2 2
	Pelagic communities	Phytoplankton Zooplankton	Phytoplankton Zooplankton	nd strong	strong strong	strong strong		nd strong	5 8	8 8	8 8	2 2	5 8	5,6 6,8	8 8
		Elasmobranchs (rays and sharks)	Benthic rays -mixed bottom -coastal Benthic-loose rays -offshore Benthic-loose rays -coastal	strong (curly ray) strong (soft stripe) strong (brunette ray)	strong (curly ray) strong (soft stripe) strong (brunette ray)	strong (curly ray) strong (soft stripe) strong (brunette ray)	strong (curly ray) strong (soft stripe) strong (brunette stingrays, stingrays) strong (curly ray)	8 8 8	8 8 8	8 8 8	8 8 8	8 2 2	8,0 6,8 6,8	8 8 8
		Cephalopods	Coastal benthics -soft bottoms		strong (cuttlefish spawning grounds)		strong (cuttlefish)	2	8	2	2		4,4	8
			Amphihalins			medium-strong		medium-strong	2	2	8	2	8	4,4	8
	Pisces		Benthic -soft bottoms Coastal benthic -rocky bottoms	strong (callionyms, spawning grounds and nurseries plaice, sole) strong (callionyms, nurseries plaice, sole) strong (gobies, shrimps)		strong (callionyma, common goby, plaice, sole, dab) 8 8 strong (paganel goby) 2 8	2 2	2 2	8 8	5,6 4,4	8 8
		Actinopterygii	Bentho-pelagic -sandy bottoms Demersals -movable funds	strong (let's launch) strong (whiting nurseries) strong (bar nurseries, whiting)	nd (gobies), strong (spawning grounds plaice, sole) strong (let's launch) strong (whiting)	2 8	8 8	2 2	8 2	8 8	5,6 5,6	8 8
			Coastal demersals -mixed bottoms			strong (gray sea bream)		strong (gray sea bream, pout)	2	2	8	2	8	4,4	8
			Demersals -mixed funds	strong (red mullet spawning grounds) strong (red mullet spawning grounds)	strong (spawning mullet, gadidae) strong (bar)	8	8	2	8	8	6,8	8
			Pelagic	strong (herring spawning grounds) strong (herring spawning grounds) strong (horse mackerel, herring)	strong (sprat, griset, mackerel, herring) 8	8	8	2	8	6,8	8
			Gannet	migratory?	weak (migratory)	migratory?	strong (wintering, migratory) migratory?	2	4	2	8	2	3,6	8
			Northern fulmar	medium (breeder)	migratory?	strong (breeder)		strong (breeder)	6	2	8	2	8	5,2	8
			Red-throated Loon	migratory?	strong (wintering)	medium (in wintering)	strong (wintering, migratory) weak (overwintering)	2	8	6	8	4	5,6	8
			Kittiwake	major (breeder)	migratory?	medium (breeder)	migratory?	strong (breeder)	10	2	6	2	8	5,6	10
			Common Guillemot	migratory?	migratory?	weak (breeder)	migratory?	migratory?	2	2	4	2	2	2,4	4
			Herring gull	migratory?	migratory?	strong (breeder)	migratory?	strong (breeder)	2	2	8	2	8	4,4	8
	Birds		Crested cormorant Brown gull	migratory? migratory?	migratory? migratory?	migratory? migratory?	migratory? migratory?	medium (breeder) migratory?	2 2	2 2	2 2	2 2	6 2	2,8 2,0	6 2
			Balearic Shearwater	migratory?	migratory?	migratory?	migratory?	migratory?	2	2	2	2	2	2,0	2
			Caugek Tern	medium (breeder)	weak (migratory)	migratory?	migratory?	migratory?	6	4	2	2	2	3,2	6
			Pygmy seagull	migratory?	migratory?	weak (breeder)	migratory?	migratory?	2	2	4	2	2	2,4	4
			Ducks (scoter)		strong (wintering)			strong (wintering)	2	8	2	2	8	4,4	8
			Curlew	medium (large plover)	strong (large plover)			medium (ring-necked plover)	6	8	2	2	6	4,8	8
			Sparrows (farlouse pipit, skylark)	nd	nd	nd	nd	nd	5	5	5	5	5	5,0	5
			Common pipistrelle	minor concern	minor concern	minor concern	minor concern	minor concern	1	1	1	1	1	1,0	1
			Common serotin	minor concern	minor concern	minor concern	minor concern	minor concern	1	1	1	1	1	1,0	1
	Bats		Pipistrelle of Nathusius Common noctule	near-threatened near-threatened	near-threatened near-threatened	near-threatened near-threatened	near-threatened near-threatened	near-threatened near-threatened	4 4	4 4	4 4	4 4	4 4	4,0 4,0	4 4
			Leiler's Noctule	near-threatened	near-threatened	near-threatened	near-threatened	near-threatened	4	4	4	4	4	4,0	4
			Two-tone serotin	insufficient data	insufficient data	insufficient data	insufficient data	insufficient data	5	5	5	5	5	5,0	5
			major	10
			strong	8
	Ecological issues DCSMM -2nd cycle		way low	6 4
			undefined	5
			no stake	2
			critically endangered	10
			vulnerable	7
	IUCN France Red List Statutes		near-threatened	4
			minor concern	1
			insufficient data	5

Respectively

2008/56/CE and 2014/89/EU directives

Funding: This work was supported by the French Ministry for a Solidary Ecological Transition under grant DRC 18 -177 311 -09156 A.

Table of contents Table 6: Priority pressures and receptors among Benthic Habitats and their Communities

For the Harbor porpoise, the Bottlenose dolphin, the Loggerhead turtle Caretta caretta, and the Leatherback turtle Dermochelys coriacea, experts concluded based on scientific evidence [START_REF] Panigada | Mediterranean fin whales at risk from fatal ship strikes[END_REF]IWC, 2018) and their own considerations of precaution that underwater collision risk increases rapidly when vessel speed in the area can be above 12 knots(case of maintenance ships, during the operation phase only). Collision risk with high speed ships appears to be the only pressure which may cause direct mortality to these species in the context of an OWF project. For both cetaceans and pinnipeds species, habitat change (mainly from the wind turbines foundations) and underwater noise (mainly during the construction phase) were identified as top priority pressures (Table 7).

Pressure Priority

Loss

Table 7: Priority pressures and receptors among Marine Mammals and Turtles

For most seabird species, similarly to cetaceans and turtles, collision is the most prominent pressure in terms of potential cumulative impacts (Table 8). Several other pressures are ranked as intermediary priority for certain species: obstacle to movement (i.e. "barrier effect"), human disturbance and loss of underwater habitat. Other pressures are associated of lower priority, but still significant: light emission and underwater habitat change.

Receptor Pressure Priority

Gray

PRIORITIZATION OF RESEARCH AREAS

The application of the methodology described in section 2.4 produced the scores presented in Table 9, and the research priorities presented in Table 10 for each ecological compartment, with no particular hierarchy among the selected research themes. The preliminary prioritization index appeared helpful and was followed in general by experts, who however found many possibilities to regroup research themes that the methodology had defined in a too detailed approach. After further elaboration, financing of the research themes will be set through collaboration with research funding organisations and public agencies. Further to research priorities attached to specific ecological compartments, some transversal research priorities were identified. For instance, experts stressed the need to improve hydraulic and sediment transport modelling, to try overcoming current difficulties of coupling atmospheric and hydraulic models, and large-scale (oceanic) and small-scale (local around windfarms structures) hydraulic models.

Table 9: "research priority index" (R) for each pair of pressure (columns) and a receptor (lines).

Experts also felt it was not always possible to be specific in terms of species, and research priorities are often more generic (Table 10). In several instances (especially for marine mammals), it was more relevant to express priorities for several pressures as a whole. For instance, the effect of non-native species

Marine reptiles

Sea turtles

Benthic habitats and communities

Marine mammals

Pinnipeds

Cetaceans

Bats

Pelagic communities

Pisces

Elasmobranchs (rays and sharks)

Actinopterygii

Birds

introduction on benthic communities may be difficult to assess separately from the effect of changes in the physical substratum (e.g. change from a soft sediment to a hard and artificialized bottom). Therefore, the use of ecosystem modelling appears necessary to study and further assess the combined effects of some pressures which interact inextricably.

Receptors Pressures Research goals

Birds Aerial habitat modification Obstacle to movement, feeding, resting, moulting in an aerial environment (leading to a loss of functional habitat)

Improve understanding of the displacement risk, through:

-Gathering information on bird's concentration and functional areas at sea -Determining changes in behaviour and area use due to offshore wind projects and their effects at the scale of a colony, then a population Aerial collisions, and pressures at source of population displacement risks Improve understanding of collision and displacement risks on population dynamics, through:

-Developing population dynamics models for selected seabird species -Collecting the demographic data necessary to configure these models and use the models to predict the probable future evolution of colonies located in France and determine whether certain colonies or populations are threatened Benthic habitats Chemical contamination (other contaminants and sources than anticorrosion devices) Improve understanding of the risk of these less studied sources and contaminants, through:

-Establishing ecotoxicity threshold values -Estimating the expected concentrations in the different environmental matrices, and characterizing the risk Development of non-native species Set up observation campaigns to monitor colonization on wind turbine infrastructures, on-site and in ports before installation.

Develop a multi-scale approach for the identification, evaluation and preventive management of the risks of the introduction of new non-native species.

Electromagnetic fields (excluding light emissions)

Identify the types and sources of electromagnetic fields generated by OWFs and relevant to benthic organisms, carry out measurement campaigns to collect basic data on EMFs in the marine environment, identify biological models and test their sensitivity to different types and levels of electromagnetic fields Depending on the results in terms of sensitivity, work could be carried out to:

-Developing or adapting models for the propagation of EMF to allow exposure estimates -Methodological development and implementation of risk assessment for benthic organisms identified in the first phase (sensitivity x exposure)

Physical pressures as a whole (habitat loss and change, substrate extraction, material deposition, and physical action on the bottom (without material extraction or deposition))

Observe seasonally over several years in the field the impact on benthic communities of the physical disturbance gradients (setting up several observation stations for reference, minimum to maximum disturbance situations, and before/after windfarm projects). Define risk indicators, risk acceptability thresholds based on ecological resilience and identify communities most at risk based on threshold exceedances. Evaluate the physical modifications on the seabed in terms of intensity and temporality (depending on the characteristics of the parks and wind turbines) Develop and test risk assessment approaches for cumulative impacts at the scale of a marine region.

Ichthyofauna

Emission of light Observe the effect of different types of light disturbances (aerial beaconing of wind turbine masts, electrical stations lighting) especially for life stages where nychthemeral migrations occur (larval stages).

Other electromagnetic fields than light Even if effects of electromagnetic fields on ichthyological communities are in general expected to be moderate, they are still poorly understood and have been identified as one of the research priorities.

Increased particle load

Although mostly a transient pressure during construction and decommissioning the effect of the increased particulate load in the water column on fish communities is poorly investigated so far and requires basic research.

Habitat loss and habitat change

The issues that require scientific investigation are the reef effect, impact on fish of benthic non-native species and the connectivity of fish populations.

Underwater noise

This priority is justified by the intensity of the pressures generated in the wind energy context., during the construction phase of course but also eventually during the operating phase. It is also justified by a less extensive knowledge than for other biological compartments, even if publications already exist, in particular on case studies in the Baltic Sea (Hammar L. et al., 2014 for example). The larval life stage will also be studied.

Marine mammals

Habitat change in a wide sense, encompassing following pressures -Substrate extraction;

-Physical action on the seabed; -Loss of an underwater habitat; -Deposition of material; -Change of underwater habitat; -Organic enrichment; -Obstacle to movement, food, rest, moulting in an underwater environment (leading to a loss of functional habitat); -Changes in activities linked to the presence of the park (e.g. fishing).

To characterize the evolution of the area and change of habitat. Seals will be predominantly affected by changes in the benthic habitats, while cetaceans predominantly in the pelagic habitats. Subsequently, to identify the change in the use of habitats by those species, based on bibliography, on data acquisition during the lifecycle and after decommissioning of windfarms (through noise data and visual observation for cetaceans, and telemetric monitoring of seals). This research needs to be conducted at the spatial scale of a seafront.

All relevant pressures in terms of demographic impact, inter alia: noise, fishing, contaminants, habitat change (detailed in the previous line), collisions.

To define populations to be studied, to produce local demographic data (observational and/or modelling) and to assess populational impacts of pressures on populations. This last step should consider several pathways between pressures and demographics, such as mortality of individuals, deterioration in the state of health of individuals, and behavioural changes in individuals.

Given uncertainty in populational modelling, developing and applying risk analysis for species taking into account uncertainties could be carried out, in order to define risk mitigation / reduction measures. , Aquatic Conserv: Mar. Freshw. Ecosyst. 11: 59-76 (2001)