Posters

Abstract

Offshore infrastructure introduce new  habitat for marine life by providing hard substrate into otherwise mostly soft-bottom environment, e.g. the southern North Sea. However, the biodiversity supported by these structures, the variation among different microhabitats, and the potential for optimization through nature-inclusive design (NID) remain insufficiently understood. To address this knowledge gap, TSO TenneT has implemented pilot measures at Offshore High Voltage Substations (OHVS) in the Dutch North Sea. Two types of artificial reef units were installed to provide shelter and foraging opportunities for reef-associated species and to stimulate reef development around the platforms. To evaluate the ecological performance of the artificial reefs and the biodiversity associated with different OHVS microhabitats, a monitoring survey was conducted by Wageningen Marine Research in June 2025 at HKN. The survey combined Remotely Operated Vehicle (ROV) video transects with environmental DNA (eDNA) sampling. At each microhabitat, ROV surveys documented habitat condition, species presence, and fish behaviour, while eDNA samples provided a molecular inventory of local biodiversity, including mobile species not easily captured by video observations. Preliminary findings indicate high biodiversity around the structures compared to the surrounding sandy environment. Notable records include a harbour seal (Phoca vitulina) and dead man’s fingers (Alcyonium digitatum) at the gabions placed over the cables. Full analyses, expected by the end of 2025, will provide insights into the ecological functioning of NID measures in offshore energy infrastructure and may be presented during the conference in April'26.