Abstract
The offshore renewable energy (ORE) sector is at a crucial moment with multiple governments enacting policies and legislation that will decisively accelerate the expansion of offshore renewable energy globally. Floating offshore wind energy will become increasingly important over the next decade and this report seeks to elucidate the potential ecosystem benefits of floating offshore wind energy developments. The known ecosystem impacts of ORE fall under 7 broad categories:
- Changes to the atmosphere and ocean/energy removal
- Sound pollution
- Electromagnetic Fields (EMF)
- Habitat modification - artificial reef effect
- Barrier effects
- Water quality – chemical pollution
- Fisheries exclusion and displacement
There is general acceptance that habitat modification and the fisheries exclusion have the potential to confer substantial ecosystem benefits, while changes to the atmosphere and ocean are tentatively identified as potentially having some ecosystem benefits. Floating offshore wind (FOW) developments are likely to result in partial or complete restrictions on fishing activities within the boundaries of a development, essentially creating non-statutory marine protected areas, also called Other Effective Area-based Conservations Measures (OECMs). This is important because overexploitation and damage from bottom trawling results in a substantial decrease in biodiversity, abundance, and biomass, particularly on benthic biogenic reef habitats, with negative implications for fundamentally important ecosystem functions and services. The exclusion of damaging activity such as trawling allows benthic habitats to recover, developing diverse and complex infaunal and epifaunal communities, attracting more mobile species, and enhancing benthic-pelagic coupling which is vital for ecosystem functioning. The evidence from existing marine protected areas highlights the ecosystem benefits of area closures, positively impacting biodiversity, abundance, organism size, and abundance compared with surrounding unprotected areas. Five key features which increase MPA efficacy are 1. no take, 2. Enforcement, 3. More than 10 years old, 4. More than 100 km2 , and 5. Isolated by deep water or sand.
FOW infrastructure can act as artificial reefs and fish aggregating devices (FADs) which increase habitat complexity and positively influence biodiversity by providing refugia, nursery grounds, and enhanced larval settlement. The degree to which FOW devices will act as FADs and artificial reefs is not well understood, however, recent surveys on the Hywind Scotland spar turbines recorded 121 epifaunal and mobile species. Evidence suggests that similar oil and gas (O&G) platforms are among the most productive marine fish habitats, comparable with designed reef habitats, benefiting pelagic and demersal fish species, and hosting diverse invertebrate communities. O&G platforms also attract a diverse range of large migratory species, including fish, sharks, reptile, marine mammals, and turtles, although, the nature of their interaction with structures remains poorly understood.
FOW farms are likely to create oceanographic change, or a wake effect, via two main mechanisms: 1) Current flows flowing around infrastructure will create a wake effect, and 2) wind flow over and around an array of turbines will create a wind shear that can generate vertical rotation in the water column, i.e., upwelling and downwelling. These wakes increase turbulence and vertical mixing which can enhance primary productivity, with positive bottom-up effects for mid and high trophic level taxa. The increased turbulence also creates valuable foraging and resting opportunities for larger mobile species.
The most likely ecosystem benefits of FOW will accrue because of area protection in combination with the artificial reef (and FAD) effect. There are possible positives and negatives associated with any oceanographic wake effect and the scale and magnitude of these is uncertain at present. The ecosystem impacts of multiple FOW developments across large continental shelf regions remain highly uncertain and research priorities need to address cumulative spatial and temporal impacts at the population level of potentially impacted species. Achieving these goals will require greater collaboration at regional and international levels, working towards shared standards of data collection and analysis, and adapting the current regulatory approach to ensure ecosystem benefits can be detected in a cost-effective manner.