Opportunities and challenges for marine ecosystem accounting at Hywind Tampen

Mul, E.J. 2025. Opportunities and challenges for marine ecosystem accounting at Hywind Tampen. NINA Report 2597. Norwegian Institute for Nature Research. This report aims to investigate the possibilities and challenges for ecosystem accounting in the marine environment around Hywind Tampen; an offshore floating wind park. Ecosystem accounting is introduced as a robust statistical framework to assess the extent and the condition of ecosystems. This report includes four main parts: 1) A literature study to identify vital differences between terrestrial and marine ecosystems, different typologies for the classification of ecosystems into ecosystem types, selection procedures for indicators for ecosystem condition and the overall status of marine ecosystem accounting. A list of (international) case studies is also presented in this part of the report. 2) The key conclusions from a workshop that was held in December 2024 are presented. 3) Ecosystem impacts resulting from offshore floating wind parks are described and a brief overview of potential mitigation measures is provided for each impact. 4) Finally, this report provides suggestions for relevant ecosystem types, ecosystem condition indicators and an overview of the impacts on each of these indicators. The potential for ecosystem extent accounts and ecosystem condition accounts are discussed. The report concludes with a list of recommendations for ecosystem accounting at Hywind Tampen. The literature study indicated that frameworks and methods for marine ecosystem accounting and biodiversity change assessments (e.g. no net loss) in marine ecosystems are much less developed and have received much less attention in literature than their terrestrial counterparts. This is largely due to the complex, 3-dimensional structure of marine ecosystems, which poses great challenges in identifying spatial explicit marine ecosystem types, measuring marine ecosystem conditions and poor data availability and quality, compared to terrestrial systems. However, recent developments in typology and selection methods for indicators can help to address these constraints. Many of the case studies for marine environments highlighted the need for transparent statistical methods, which include an evaluation of the uncertainty. The potential effects of offshore floating wind parks can be grouped into 6 overarching categories: 1) Entanglement, 2) Habitat alteration (including displacement effects), 3) Collision, 4) effects of sound, light or electromagnetic fields, 5) water quality, and 6) atmospheric and oceanic effects. For each of these impacts, mitigation measures are presented. Four ecosystem types are identified for the Hywind Tampen area: Aphotic saltwater sediment bottom (soft-sediment bottom habitat, where no light penetrates), Aphotic marine water systems (lower part of the water column, where no sunlight penetrates), Euphotic marine water systems (upper part of the water column, where sunlight is available) and Heavily modified or new marine structures (artificial hard substrate at the bottom or at the surface). For each ecosystem type a list of ecosystem condition indicators is presented. Habitat loss is a much more important driver in terrestrial ecosystems than in marine ecosystems, where changes in ecosystem condition are often more complex. Indicating the status of ecosystem health based on biodiversity alone may therefore not be sufficient for marine ecosystems. A more suitable approach would be the assessment of a range of ecosystem indicators, including biodiversity, through a Panel-Based Assessment of Ecosystem Condition (PAEC). Perhaps the greatest potential for offshore floating wind parks in mitigating ecological impacts is by addressing ecological issues that may not be caused by the wind parks themselves. This can be achieved for example by the implementation of nature-based solutions, or by the development of coexistence with other human activities or with offshore carbon capture and storage initiatives.

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