Future coastal ecosystems will be challenged with a multitude of ecosystem-level stressors, resulting from both local anthropogenic activities and environmental change acting at the global scale. The installation of offshore wind farms (OWFs) is currently a major human activity in the coastal North Sea area, resulting in the introduction of large surfaces of artificial hard substrates (AHSs) in an otherwise sandy environment. At the moment, 3230 offshore wind turbines are operational in European seas and more OWFs are planned in the near future. This AFIS are rapidly colonized by large quantities of fouling fauna, including non-indigenous species (NIS). This in turn attracts fish and large crustaceans, affects local phytoplankton communities and changes local sediment properties and inhabiting fauna.

Coastal ecosystems are well-known sites of N-removal through microbial activity, thereby counteracting eutrophication processes. A drawback of this process is the production of N2O during the first step of nitrification or by 'nitrifier denitrification'. N2O is a highly potent greenhouse gas that significantly contributes to global warming and the destruction of the stratospheric ozone layer. While the effect of macrobiota on N-cycling is mainly investigated in sediments, there is recent evidence that fouling fauna can contribute substantially to N2O production, either through their own activity or through their microbiome. As such, the presence of large quantities of fouling fauna on AHRs can have important consequence for the air-sea exchange of greenhouse gasses in coastal areas.

Coastal areas also harbor important commercial activities. However, space at sea is limited, and multiple use of some areas is considered beneficial. The Belgian marine spatial plan allows aquaculture activities in the OWF concession area, and a recent study has shown that mussel culture in OWFs can indeed be profitable. Mussel culture pilot projects have been initiated in the past in the Belgian part of the North Sea (BPNS) and mussel culture activities in OWF concession areas are now being incorporated in the roadmap towards integrated aquaculture in Flanders. The effect of local anthropogenic impacts on the coastal ecosystem should be investigated in the context of global impacts on the marine environment. Increased atmospheric CO2 concentrations lead to global warming on the one hand, and on the other hand to a decrease in ocean pH (ocean acidification, OA) and concentration of carbonated minerals. In coastal North Sea areas, the OA rates are shown to be one order of magnitude faster than predicted for the open ocean. The limited studies available investigating the combined effect of OA and warming on an ecosystem-wide level reveal substantial, non-additive and complex changes in community dynamics. In addition, OA affects both the pelagic and the benthic nitrogen cycling, while inducing metabolic depression and a lowered resistance to pathogens in blue mussels.

The general objective of PERSUADE is therefore to investigate ecosystem-wide responses to local and global stressors to quantify how future anthropogenic activities will contribute to the production of the greenhouse gas N2O in a future climate setting, by quantifying the interactions between the biotic and abiotic compartments in an OWF environment. At the same time, we will investigate how the transfer of energy among the different compartments of the coastal ecosystem will evolve. By integrating the results in an ecosystem model, we will be able to run climate impact scenarios at scales (temporal, ecosystem-wide, with and without aquaculture) that are relevant for the sustainable management of the coastal ecosystem