In 2023 Natural England was commissioned by Defra to define Marine Irreplaceable Habitats (MIH) and to develop a method for mapping them in English seas. The Marine Biological Association (MBA) and Plymouth Marine Laboratory were contracted to deliver the work.
The initial Phase 1 of this work developed a working definition, identifying Marine Irreplaceable Habitats as “those which cannot be successfully restored or created because they are either very difficult to restore and / or very slow to recover” once damaged or destroyed. A set of criteria was established to describe irreplaceability, which included recoverability, restoration feasibility, rarity, and uniqueness. Marine habitats were then individually scored against these criteria.
The second phase updated the scoring and developed a method for mapping MIH scores in English waters. The outputs of this work offer a valuable tool for identifying exceptionally vulnerable habitats, and informing the development of an MIH heatmap in the future. Establishing understanding of what makes habitats more difficult to replace and where the high scoring MIH are located in English waters will support nature-positive marine development.
The MIH definition and scoring system does not define a legal threshold or statutory designation but provides further evidence to highlight areas where restoration is most likely to be very difficult, slow, or unfeasible. This MIH work is not statutory guidance and not policy. It is also currently independent from terrestrial Irreplaceable Habitats statutory guidance. The MIH definition and scores may help to inform strategic planning decisions.
Please send any questions about this report to marinenetgain@naturalengland.org.uk
Technical Report (May 2026 latest version).