Modification of benthic ecosystems by offshore wind farms: implications for natural capital and ecosystem services

Due to concerns about climate change and energy security there has been considerable growth in the installed capacity of offshore wind energy worldwide over the last two decades. Owing to engineering constraints offshore wind turbines have generally been installed in areas characterised by soft sediments. Offshore wind farms introduce hard substrate and intertidal zones into these areas and have the capacity to alter natural capital, including biodiversity, in benthic ecosystems. Changes in benthic habitats may result in changes to the ecosystem services (goods and benefits people receive from nature) provided by natural functions and processes. Thus, continued expansion in offshore wind energy has the potential to affect natural capital and the associated delivery of ecosystem services. Differences in benthic community composition between manufactured structures, natural rock reefs and soft sediments in the southern North Sea were found to be significant (P <0.05) through permutational analysis of variance (PERMANOVA). However, evidence suggests that ecosystem functioning remained similar between natural substrata and offshore energy structures. Based on a Monte-Carlo analysis there were no significant differences in trait expression between the habitat types for the most dominant taxa. There were significant differences in feeding mode, longevity and larval duration amongst less common taxa (P <0.05), however their effect is likely to be muted. An assessment of natural capital demonstrated that offshore wind farms present risks and benefits to natural capital and the associated ecosystem services. The Thanet offshore wind farm was used as a case study. Overall, the natural capital increased following the installation of the wind farm. Targeted investment to support natural capital within offshore wind farms can produce functional ecosystems that not only produce low carbon energy but also augment ecosystem services; a number of which can have economic benefits. The findings have implications for the design, operation, maintenance and end of life treatment of offshore windfarms.