With the increasing amount of energy-related infrastructure (oil and gas platforms, wind turbines, cables) installed in the North Sea, there is a need to understand the role these man-made structures (MMS) play in the marine ecosystem. Current decommissioning regulations prohibit leaving installations in place in any form, which means complete removal when no longer in production. However, there are significant knowledge gaps on the effect these MMS have on marine ecosystem function. Central to our understanding of MMS on the ecology of the North Sea, is having a better understanding of the background (baseline or equilibrium position) against which changes in ecosystem processes can be assessed. A few recent studies have identified the role of MMS as artificial reef structures, yet little research has examined the effect of MMS on the largest surrounding habitat - the seabed, its associated biodiversity, and the ecosystem services it provides.

Shelf sediments, such as those found in the North Sea, are dominated by sandy permeable sediments, and recent research under the NERC Shelf Seas Biogeochemistry programme established that a significant proportion of 'blue carbon' is held in such shelf sediments. These sediments provide a variety of ecosystem services, from biogeochemical cycling of nutrients, carbon and oxygen; biodiversity (macrofauna, microbial); contaminant deposition; habitat provision; and production of inorganic nutrients to support surface water productivity, underpinning marine food webs and commercial fisheries. The presence and installation of MMS provides protection of the seabed from other human activities, such as trawling and dredging, protecting the seabed from physical disturbance and effectively providing an unofficial 'Marine Protected Area' (MPA). The hydrocarbon extraction activity at MMS influences local biodiversity, particularly changing benthic microbial diversity as a response to the presence and concentration of associated contaminants, and these microorganisms play a vital role in degrading the hydrocarbons within the sediments. Whilst the stability of these sediments and their ability to sequester carbon is uncertain, the decommissioning and physical removal of MMS is likely to disrupt these long term carbon stores, and impact on benthic ecosystem processes. Complete removal of MMS, following current Oslo-Paris (OSPAR) regulations could impact on the hydrodynamics and nutrient cycling at a local scale, negatively affecting biodiversity, carbon sequestration, and ecosystem processes in surrounding sediments. Furthermore, the shelf sediments may be exposed to additional hydrocarbon contaminants either via oil seeps/pipeline leaks or resuspension of oily drill cuttings, and their eventual disturbance and wider impact is relatively unknown.

The presence and subsequent removal of MMS will therefore not only likely affect the sediment biogeochemistry but also the marine biodiversity and ecosystem function. This project addresses this knowledge gap through novel technologies (Autonomous Underwater Vehicles) and environmental DNA 'eDNA', with modelling of environmental data alongside data from industry (INSITE Interactive and our industry partners) to identify the role of MMS on key marine ecosystem processes. We have a strong team of project partners from industry (Shell, Repsol, INEOS, DNV-GL) and stakeholders (Shetland Oil Terminal Advisory Group, SOTEAG; National Subsea Research Initiative, NSRI).

This project has significant support from industry and stakeholders, and a Stakeholder Advisory Group will be established to make full use of this. Recent news reports on UK decommissioning decisions have drawn attention other European oil nations on what is environmentally acceptable, thus the outputs of this project are expected to have international interest and direct policy relevance for future decommissioning.

Potential Impact:
Who will benefit? FuECoMMS takes a multidisciplinary approach to better understand the role of man-made structures in the North Sea, and how decommissioning these infrastructure may impact the marine ecosystem. There are several beneficiaries, particularly in industry (oil and gas companies, renewable energy companies) and policy (Defra, OSPAR, Cefas). To ensure maximum impact of scientific results, there are a number of industry partners (Shell, Repsol, INEOS, DNV-GL) and stakeholders (Shetland Oil Terminal Environmental Advisory Group (SOTEAG), National Subsea Research Initiative (NSRI)) that have confirmed participation in the project and dissemination of results. The findings will underpin future recommendations for decommissioning practice. The project will also benefit academics, and users of the North Sea (e.g. commercial fisheries).

How will they benefit? Project outputs have the potential to inform industry on the best guidelines for decommissioning of man-made structures, and provide a basis for a change in decommissioning policy:
1. A robust dataset including micro- and macro- biodiversity (collected through traditional and eDNA approaches) alongside biogeochemical parameters related to presence and removal of man-made structures (MMS). This will provide a baseline reference for measuring impacts.
2. Identify the role of inherent seabed diversity (driven by microbial assemblages) in remediation following release of pollutants through decommissioning of infrastructure. This will feed directly into future management plans for decommissioning.
3. Provide evidence of ecosystem services (e.g. carbon storage) that may be disrupted during physical removal of man-made structures.
4. The microbial metagenetic and abundance data alongside sediment chemistry and toxicity data will inform industry of how microbial functional diversity changes following exposure to MMS associated contaminants through biotransformation and detoxification.
5. Combined datasets obtained from this project will identify which parameters are most relevant for ascertaining impact of MMS on functional marine diversity under different decommissioning scenarios in relation to specific environmental parameters.
6. The project will produce a trained PDRA with molecular, analytical, modelling and industry-relevant skills who can enter private/public sector marketplace, and have broad skills that can be used across academia, Government sectors and industry.
7. Enhance dialogue between researchers, industry, stakeholders and end-users in influencing future recommendations for decommissioning, and installation, of man-made structures in the North Sea, and globally.
8. Produce industry-relevant summary of scientific outputs to form the basis of a decommissioning recommendations framework, in dialogue with stakeholder advisory group members.