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Offshore platforms, subsea pipelines, wells and related fixed structures supporting the oil and gas (O&G) industry are prevalent in oceans across the globe, with many approaching the end of their operational life and requiring decommissioning. Although structures can possess high ecological diversity and productivity, information on how they interact with broader ecological processes remains unclear. Here, we review the current state of knowledge on the role of O&G infrastructure in maintaining, altering or enhancing ecological connectivity with natural marine habitats. There is a paucity of studies on the subject with only 33 papers specifically targeting connectivity and O&G structures, although other studies provide important related information.Evidence for O&G structures facilitating vertical and horizontal seascape connectivity exists for larvae and mobile adult invertebrates, fish and megafauna; including threatened and commercially important species. The degree to which these structures represent a beneficial or detrimental net impact remains unclear, is complex and ultimately needs more research to determine the extent to which natural connectivity networks are conserved, enhanced or disrupted. We discuss the potential impacts of different decommissioning approaches on seascape connectivity and identify, through expert elicitation, critical knowledge gaps that, if addressed, may further inform decision making for the life cycle of O&G infrastructure, with relevance for other industries (e.g. renewables). The most highly ranked critical knowledge gap was a need to understand how O&G structures modify and influence the movement patterns of mobile species and dispersal stages of sessile marine species. Understanding how different decommissioning options affect species survival and movement was also highly ranked, as was understanding the extent to which O&G structures contribute to extending species distributions by providing rest stops, foraging habitat, and stepping stones. These

The Oslo and Paris Commissions (OSPAR) decision 98/3 prohibits the dumping of man-made structures (MMS) offshore. However, there are regions of the world where MMS are recognized as providing an ecological and societal benefit through the provision of ecosystem goods and services. This review provides a commentary on our current understanding of the ecological influence of man-made structures, the consequences of their decommissioning and recognizes that our knowledge is far from complete. It is known that a diverse and complex ecosystem of attached organisms develops on submerged structures which supports a localized food web that could not exist without them. However, our lack of detailed information makes modelling of system response to decommissioning very tentative. Ideally, we should use the best possible scientific information to reach a consensus as to whether the blanket removal of MMS (excepting derogations) is the most environmentally supportable option. The evidence available to-date shows both benefits and some risk in leaving MMS in place and this needs to be examined without preconception. On the UKCS, MMS as artificial habitats are not considered under the Habitats Directive, irrespective of the value or rarity of the species present. We conclude that a more comprehensive regulatory process, together with the recognition of the ecology associated with man-made structures, would allow science to play a role in the decision-making rather than supporting a blanket policy ignoring ecological context.