The North Sea is one of the most industrialised marine environments on the planet, with thousands of man-made structures (MMS) including oil and gas platforms, pipelines, subsea cable routes, and marine renewable energy installations. Much of the infrastructure relating to the oil and gas industry is coming to the end of its economic life, while the marine renewable energy industry is expanding rapidly. Current legislation requires that (with some exceptions) MMS in the North Sea should be removed from the marine environment after their operational lifespan is complete. Decommissioning of the UK oil and gas sector will cost around £50 billion, with almost half of the financial burden falling on the taxpayer.

These forthcoming changes in the North Sea landscape may have a significant impact on marine life. There is mounting evidence that the effects of MMS on the local marine environment are complex, and depend on the age, type, and operational status of the MMS. Once installed, MMS can host artificial reefs supporting diverse communities of marine life. The exclusion of shipping and fishing in the vicinity of many MMS may also provide refuges for fish and predators such as sharks, seals or porpoises (de facto Marine Protected Areas). However, the true extent of the effects of MMS on the ecosystem are unclear. To ensure effective decision-making about removal and installation of such structures in the future, there is an urgent need to better understand the impact of MMS on the North Sea ecosystem.

The below video from Russell et al. (2014) shows the track of a harbour seal tagged with a GPS device repeatedly foraging at a windfarm in the North Sea.

1. Quantify the impact of, and overlap between, man-made structures (MMS) and North Sea marine mammal distributions
2. Estimate what proportion of seal and harbour porpoise populations forage at MMS.
3. Examine how species-specific changes in fish abundance affect consumption by seals and porpoises.
4. Assess how MMS affect benthic fauna community composition, structure and function.
5. Integrate outputs from 1-4 with existing data and knowledge of fish, food webs and fisheries, within a North Sea ecosystem model (developed in INSITE I), to predict the impact of the current, and potential future, MMS landscape on the ecosystem.

For further detail on EcoSTAR objectives and associated work packages, click here.

Man-made structures and Apex Predators: Spatial interactions and overlap (MAPS)
The MAPS project (led by Debbie Russell, featuring Philip Hammond) sought to use existing datasets to establish the magnitude of the effects of man-made structures compared to the spatial and temporal variability of the North Sea ecosystem, with regard to apex predators. MAPS considered the association between structure presence and apex predators on two spatial scales: (1) at the scale of the North Sea using species’ distributions and (2) at a very fine spatial scale using the movements of individuals in relation to structures. Overall, results suggested that for the marine predators considered, the current North Sea oil & gas infrastructure was not a key driver of at-sea distribution, nor did it influence the foraging behaviour of the considered seabird species at a population level. However, it should be noted that in order to maximise power to detect effects of structure presence on predator distribution and foraging, different structures types were pooled. This means that impacts restricted to a certain structure type or age, may not have been detectable. The project concluded that additional data on fine scale movements of apex predators and on oil & gas structures (e.g. which sections of pipelines are exposed) are required to determine the impact of different structure types and ages on species’ distributions and behaviour.

Download the report here

Investigating food web effects due to man-made structures using COupled Spatial Modelling (COSM)
The COSM project (led by Christopher Lynam and Clement Garcia) aimed to better understand if the presence of man-made structures might lead to changes locally that can spread through the wider ecosystem through predator-prey interactions and dispersal. This was delivered through the collation of existing data, statistical modelling of data, and the development of a spatial food web model that can be projected through time. The food web model was used to evaluate scenarios: asking the question, what would happen to communities if structures were removed through decommissioning? Which species might be affected? The main findings were that: (1) man-made structures have an effect on the local community composition and these effects can disperse throughout the North Sea ecosystem mediated by interactions between species; (2) the removal of oil and gas platforms and pipelines may ultimately contribute to declines in some groups (rays and sand eels), but increases in others (sharks, flatfish and roundfish); (3) the presence of wrecks and wind turbines appears to have a much greater impact than oil and gas infrastructure on rays, sharks, sand eels, flatfish and demersal roundfish; (4) all modelled effects of structures are minor compared to the potential effect of other pressures such as an increase in temperature on the ecosystem or increase in fishing effort to historic levels; and (5) although the additional habitat provided by platforms and pipelines may be relatively small, this difference should not be disregarded at this stage for non-commercial species of conservation concern, since natural variability is by its very nature unmanageable and the removal of other structures such as wrecks is unlikely to occur in great amount.

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UNDerstanding the INfluence of man-made structures on the Ecosystem functions of the North Sea (UNDINE)
The UNDINE project (led by Silvana Birchenough and Clement Garcia) aimed at enhancing our current understanding of how MMS could modify ecological processes over several scales; this based particularly on examining existing data with analytical tools, providing insight into the ecosystem functioning (e.g. food web modelling and connectivity modelling). The project examined how the introduction of MMSs affected ecological processes, mainly: (1) understanding the effects on ecosystem functioning both on the MMS and in the surrounding soft sediment areas (i.e. functional artificial reef effect; and (2) validating the enhanced connectivity of hard substrate species (i.e. stepping-stone effect). Some of the key findings included that: spatial and temporal patterns in community structure and secondary production values revealed clear responses (e.g. over time and depth gradients), supported by the persistence of biological traits over time and across all structures; clear modifications in the upper parts of MMSs, where the highest production values and potential biomass export to soft bottoms were observed; an increased carbon retention capacity at offshore wind farms when compared to oil and gas platforms; the blue mussel Mytilus edulis, is a key organism responsible for the high carbon retention capacity at offshore windfarms when compared to oil and gas platforms or natural sediments; the pool of species present on MMS is determined by the arrival of constant species propagules and a subsequent local survival of hard substrate species.

Download the report here