Artificial hard-substrate colonisation in the offshore Hywind Scotland Pilot Park

Abstract

Abstract. Artificial substrates associated with renewable offshore energy infrastructure, such as floating offshore wind farms, enable the establishment of benthic communities with a taxonomic composition similar to that of naturally occurring rocky intertidal habitats. The size of the biodiversity impact and the structural changes in benthic habitats will depend on the selected locations. The aim of the study is to assess colonisation and zonation, quantify diversity and abundance, and identify any non-indigenous species present within the wind farm area, as well as to describe changes in the epifouling growth between 2018 and 2020, with regards to coverage and thickness. This article is based on work undertaken within the offshore floating Hywind Scotland Pilot Park, the first floating offshore wind park established in the world, located approximately 25 km east of Peterhead, Scotland. The floating pilot park is situated in water depths of approximately 120 m, with a seabed characterised predominantly by sand and gravel substrates with occasional patches of mixed sediments. The study utilised a work class remotely operated vehicle with a mounted high-definition video camera, deployed from the survey vessel M/V Stril Explorer. A total of 41 structures, as well as their associated sub-components, including turbines substructures, mooring lines, suction anchors and infield cables, were analysed with regards to diversity, abundance, colonisation, coverage and zonation. This approach provides comprehensive coverage of whole structures in a safe and time-saving manner. A total of 11 phyla with 121 different taxa were observed, with macrofauna as well as macroalgae and filamentous algae being identified on the different structures. The submerged turbines measured approximately 80 m in height and exhibited distinct patterns of zonation. Plumose anemones (Metridium senile) and tube-building fan worms (Spirobranchus sp.) dominated the bottom and mid-sections (80–20 m) of the turbines, while kelp and other Phaeophyceae with blue mussels (Mytilus spp.) dominated top sections of the turbines (20–0 m). A general increase in the coverage of the epifouling growth between 2018 and 2020 was observed, whereas the change in thickness between years was more variable.