An ecosystem model for assessing potential impacts of offshore windfarm on Eastern English Channel ecosystem

The development of offshore windfarms (OWF) is crucial for the energy transition to achieve decarbonisation targets. However, the ecological effects of this expansion remain largely unexplored. This study use the OSMOSE model to investigate the potential impacts of OWF in the Eastern English Channel (EEC) ecosystem. The primary objective is to 1) improve the assessment of OWF effects on ecosystems by integrating multiple pressures within a single modelling framework, and 2) analyse ecosystem responses under various OWF deployment and fishing restriction scenarios.

The OSMOSE model is a multispecies, individual-based model that relies on opportunistic predation. It was calibrated to reproduce observed trends of biomass, catch, and catch at length in the study area from 2002-2022. The model's emergent properties (e.g., growth, food web structure) were validated to ensure ecological realism.

A factorial plan of simulations, incorporating OWF deployment and fishing restriction scenarios, provides ecosystem projections up to 2050. The OWF deployment scenarios include: 1) cost minimization, 2) exclusion from regulatory environmental protection zones, 3) long distance from the coast, and 4) a balanced scenario that combines elements from the previous three. The fishing restriction scenarios include: 1) no fishing closure, 2) closure for trawlers, and 3) closure for all fishing fleets. To represent potential OWF impacts, the simulations considered fishing restrictions during the operational phase and the following factors during the construction phase: fishing access restrictions, underwater noise, and sediment resuspension. Biomass, yield, and size-dependent indicators were analysed in a spatially and temporally explicit manner to provide insights into the OWF impact on different aspects of the EEC ecosystem.

At the scale of the entire study area, we observed a slight influence of OWF on total biomass and total catch. However, size-based indicators showed an increasing trend under certain scenarios, suggesting a potential reserve effect. At the individual OWF scale, the response of these indicators varied across different areas. This study highlights the importance of considering both the specific deployment sites and fishing regulations in cumulative impact assessments of OWF.