Influence of offshore oil and gas structures on seascape ecological connectivity

Abstract

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 questions could be addressed with further dedicated studies of animal movement in relation to structures using telemetry, molecular techniques and movement models. Our review and these priority questions provide a roadmap for advancing research needed to support evidence-based decision making for decommissioning O&G infrastructure.

Keywords: birds; ecosystem function; fish; hydrodynamics; invasive species; larval dispersal; marine megafauna; particle tracking; subsea infrastructure.

FIGURE 1

Examples of different offshore O&G infrastructure including (a) steel platform for methane extraction located in the Ionian Sea (Central Mediterranean Sea), (b) A18 gas‐production platform (North Sea), (c) Harriet Alpha conventional steel platform and flare, (d) and (e) subsea pipelines, (f) and (g) subsea wells. (Photographs from authors)

FIGURE 2

Schematic diagram illustrating (a) how O&G structures could provide connections (weight of line indicative of strength of connection) between natural environments or between other structures and the natural environment, potentially enhancing the connectivity (or connectedness) of a system by adding nodes and (b) relevant processes associated with seascape connectivity influenced by O&G structures. A platform jacket, vessel, subsea wells (yellow), pipeline (grey) and flowlines (black) are indicated. Dashed arrows indicate movements of organisms along pipelines and between structures and surrounding natural ecosystems, either on the seabed, in the water column, or above the surface in the case of seabirds (e.g. storm petrels, sea ducks)

FIGURE 3

Extent of offshore O&G infrastructure and hotspots of marine biodiversity. Spatial layer of O&G infrastructure was obtained from Lujala et al. (2007). Taxa occurrence data from AquaMaps (Kaschner et al., 2019) and GBIF (GIBF 29 March 2021). Infrastructure layer is indicative of the presence of O&G only and does not represent footprint covered. See Methods S1 for details. (a) Indo‐Pacific region, (b) Europe, Mediterranean, eastern Atlantic Ocean and northern Indian Ocean, (c) Northern America and Gulf of Mexico, (d) South America

FIGURE 4

Summary of literature and expert opinion that informed this review and identification of priority research questions. (a) Relative contribution of each of the study areas of ecology and connectivity (see Data S1) with respect to O&G infrastructure that were identified during the literature search and via expert contribution. The size of each pie chart is related to the total number of studies in each region, with the legend indicating the reference size for a total (15 studies used as an example). (b) Expert‐identified top 16 priority science questions to address knowledge gaps (Section 8—Table 1, Table S2; Figure S1) showing the number of original questions within each over‐arching science question and number of votes each priority area received (see Data S1); (c) Expert (n = 46) self‐assessed knowledge of the subject areas of this review from 1 (low familiarity) to 5 (expert knowledge)

FIGURE 5

Fauna associations with offshore O&G infrastructure; (a) black guillemots on platform, (b) green turtle beside a subsea O&G structure, (c) Mytilus sp. mussels on jack‐up‐rig leg, (d) grey seal resting on North Sea oil platform, (e) Metridium senile anemones on jack‐up‐rig leg, (f) whale shark beneath platform, north‐west Australia, (g) Tubastraea sp. on a platform, north‐west Australia, (h) harbour porpoise mother and calf by a North Sea oil rig, (i) shoals of bait fish beneath a flare tower, north‐west Australia, (j) Australian giant whelk egg casing beside a subsea pipeline, (k) soft coral communities colonising a subsea pipeline and (l) bluefin tuna and feeding basking shark by a North Sea oil rig. (Photographs provided by authors)