Fish associations with shallow water subsea pipelines compared to surrounding reef and soft sediment habitats

Karl D Schramm,Christopher M Jones,Travis S Elsdon,Benjamin J Saunders,Euan S Harvey,Stephen J Newman,Michael J Marnane

doi:10.1038/s41598-021-85396-y

Karl D Schramm, Christopher M Jones + Show 5 more

Open Access

https://doi.org/10.1038/s41598-021-85396-y

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Abstract

Offshore decommissioning activities are expected to increase as oil and gas subsea infrastructure becomes obsolete. Decisions on decommissioning alternatives will benefit from quantifying and understanding the marine communities associated with these structures. As a case study, fish assemblages associated with an inshore network of subsea pipelines located on the North West shelf of Western Australia were compared to those in surrounding natural reef and soft sediment habitats using remotely operated vehicles fitted with a stereo-video system (stereo-ROVs). The number of species, the abundance, biomass, feeding guild composition and the economic value of fishes were compared among habitats. The community composition of fish associated with pipelines was distinct from those associated with natural habitats, and was characterised by a greater abundance and/or biomass of fish from higher trophic levels (e.g. piscivores, generalist carnivores and invertivores), including many species considered to be of value to commercial and recreational fishers. Biomass of fish on pipelines was, on average, 20 times greater than soft sediments, and was similar to natural reefs. However, the biomass of species considered important to fisheries recorded on the pipelines was, on average 3.5 times greater than reef and 44.5 times greater than soft sediment habitats. This study demonstrates that fish assemblages on the pipeline infrastructure exhibit high ecological and socioeconomic values.

Highlights

Offshore decommissioning activities are expected to increase as oil and gas subsea infrastructure becomes obsolete
This study aims to compare fish assemblages on exposed shallowwater subsea pipelines to those observed in nearby natural reef and soft sediment habitats using stereo-remotely operated vehicle (ROV)
The mean number of species varied between habitats (PERMANOVA: F2,382 = 125.82, P < 0.001) with reef having significantly more species than pipeline (P(pairwise) = 0.008) and soft sediment habitats (P(pairwise) < 0.001), which were different from one another (pipeline and soft sediment: P < 0.001) (Fig. 4a)

Summary

Introduction

Offshore decommissioning activities are expected to increase as oil and gas subsea infrastructure becomes obsolete. With growing evidence that oil and gas structures have the potential to function as artificial reefs (e.g.6–12), there is a compelling environmental case for consideration of in situ decommissioning alternatives. These alternatives include leaving the infrastructure in place, partial removal, toppling onto the seafloor or relocating to a designated reefing site[3,13,14]. Studies specific to north Western Australia[29,32,33] have documented a high diversity and abundance of fish on pipelines, including species that are considered important to fisheries (e.g. lutjanids (snappers) and epinephelids (groupers)). Higher distributions of fish were observed near spanning pipelines (i.e. unsupported pipe where seabed sediment has been removed by water flow scouring), suggesting that these structures may be favourable places for refuge and access to food (e.g. ambush behaviours) for some s pecies[29,32,33]

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