Defining Marine Irreplaceable Habitats.

Published online
16 May 2023
Published by
Natural England
Content type

Tillin, H. M. & Watson, A. & Tyler-Walters, H. & Mieszkowska, N. & Hiscock, K.

Publication language
UK & England


Understanding which habitats should be considered irreplaceable in the marine environment is important for Natural England's marine casework and in new areas of work such as marine net gain. Knowing which habitats are irreplaceable will assist developers, planners and regulators to avoid habitats that cannot be replaced or recreated elsewhere in compensation for their loss. The Marine Biological Association of the UK (MBA) was commissioned by Natural England to define marine habitat irreplaceability and define coastal and marine irreplaceable habitats. The commissioned project consisted of three stages: Stage 1: A literature review on definitions of marine habitat irreplaceability. Stage 2: Interviews with experts to further discuss and refine criteria for marine habitat irreplaceability. Stage 3: Application of methodology to assess irreplaceability to UK Level 3 and 4 EUNIS habitats. Stage 1: To inform the development of a definition of marine irreplaceable habitats the MBA team undertook a literature review that evaluated a wide range of sources. The review identified a number of criteria, primarily from biodiversity conservation science and initiatives that are relevant to assessing irreplaceability and the value of marine habitats. No specific definition of marine habitat irreplaceability was sourced that had been previously developed and applied. A shortened version of the review is provided in this project report as a technical appendix. Stage 2: To support expert interviews of the project, the literature review was supplied as a stand-alone document to a range of experts in marine management, policy and ecology who were then interviewed. The expert interviewees provided a range of perspectives and comments. Key discussion points focussed on: (i) criteria that should be included or excluded, (ii) terminology and (iii) applicability of a national generic definition of marine habitat irreplaceability based on the UK Marine Habitat Classification versus regional and local assessments. The majority of interviewees suggested that core criteria for irreplaceability should include recovery and ease of restoration, rarity and uniqueness. Irreplaceability criteria based on connectivity, function and delivery of ecosystem services were considered important by interviewee, but are more applicable to regional and local decision making and management and not possible to assess based on the generic UK Marine Habitat Classification. Following the interviews, the definition of irreplaceable marine habitats was refined to: "Marine Irreplaceable habitats are those which cannot be successfully restored or created based on one or more of the following factors: * They are *very difficult to restore or **very slow to recover: * very difficult refers t, feasibility and cost: difficult in-situ restoration would be that which requires significant technical input- including maintenance, supporting infrastructure and for which there are low rates of success. * refers t, very slow (> 25 years) based on the MarLIN recovery scale and supported by information on pressures including abrasion, penetration and sediment disturbance and extraction. Create refers t, ex-situ creation of the habitat (could be considered replacement) difficulties could result from availability of suitable habitats-supported by environmental context assessments or difficulty of creation- including translocation. Assume that habitats that are difficult t, restore are als, difficult t, create. They may be nationally rare (based on extent, range and distribution) and/or have an unusual or rare environmental context. This definition should be considered as a draft, the aim is t, continue t, discuss the use of this definition following publication of this report. Stage 3: Based on previous projects and online UK Marine Habitat Classification resources, coastal and marine habitats that are present in English waters from mean high water out t, the limit of the English Exclusive Economic Zone were identified. A systematic assessment of the irreplaceability of these was undertaken based on the following criteria: natural recovery potential (years t, recover), rarity (based on number of records and regional distribution), and the environmental context (physical habitat, hydrodynamics) and rarity/distinctiveness of the biological assemblage. Categories were created t, assess each criterion with weighted scores assigned t, each category. Scores were summed t, provide an overall score for irreplaceability for each habitat. The irreplaceability assessment evaluated 32 UK EUNIS Level 3 broad-scale habitats, 79 EUNIS Level 4 biotope complexes and 225 EUNIS Level 5 biotopes. EUNIS Level 6 sub-biotopes were only assessed if they were considered likely t, be irreplaceable based on characteristics such as the substratum and only twelve of these were assessed. N, threshold for scoring was identified at which a habitat moves from being considered replaceable t, irreplaceable. Any habitat that scored highly for any of the assessed criteria may pose challenges for recovery, restoration or recreation. However, habitats that score above 40 were considered t, score highly against the assessed irreplaceability criteria and, therefore, may be a combination of slow recovering, unfeasible t, recreate, rare or unique. Nine (28%) of the assessed EUNIS Level 3 broad-scale habitats scored highly (≥40) for irreplaceability. These were all habitats that were either characterised by long-lived slow-growing species, or were restricted physical features (seeps and vents), or deep-sea habitats (as these occur only in part of one of the assessed regions). At EUNIS Level 4, ten (12%) biotope complexes scored highly and at EUNIS Level 5, 21 (9%) biotopes were high scoring. Irreplaceability scores were frequently very variable between constituent biotopes within EUNIS Level 4 and 5 habitats. An assessment showed that most habitats that score highly against irreplaceability criteria are recognised through Marine Protected Area (MPA) designations, conservation targets and lists of conservation interest habitats and features. The project outputs include this technical report and an Excel spreadsheet, which provides an audit trail of the evidence and decisions made and summary scores.

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