Offshore man-made structures: to remove or not to remove?

21 April 2020

illustrated graphical abstract

Man-made structures have been built into our coastal and marine environments as we respond to the need to generate even more energy. Installed across several soft sediment environments, these structures range from oil and gas installations to harbour walls, wrecks, pipelines, and offshore wind farms.

Inevitably, these structures host fouling communities that are often new to the offshore regions - potentially serving as stepping-stones for non-indigenous species as well as providing habitat and shelter for a variety of marine species.

The altered local biodiversity affects biological and biogeochemical processes from the water column to the seafloor, either directly (e.g. scouring, organic matter export from piles) or indirectly (e.g. closure or displacement of fisheries) and, hence, ecosystem functioning is also affected at various spatial and temporal scales. ​

But what should happen to these structures when they have been decommissioned? This debate provides the focus of the latest themed article set in ICES Journal of Marine Science, which presents a compilation of new evidence. Decommissioned offshore man-made installations has been spearheaded by Silvana Birchenough, Cefas​, and Steven Degraer, Royal Belgian Institute of Natural Sciences​.  “There are 14 peer-reviewed papers helping to shape the science-based evidence", says Birchenough, “This new research will support ongoing discussions to inform marine spatial planning and future policy decisions on the use and protection of marine resources". The ecological best practice in decommissioningrigs/renewables-to-reefs, the influence of man-made infrastructures on fish population dynamics, and commercial fisheries losses arising from offshore pipelines are a few of the research topics included.​​

Research

Joop Coolen, Wageningen Marine Research, has been working on the impact of offshore infrastructure for many years and is very pleased with such an interesting collection of scientific work put together for this themed set. "I work mostly on fouling biodiversity on oil and gas installations. Whether or not the artificial reef role these structures play should be considered in decommissioning decisions has been an important discussion point." The research Coolen presents facilitates this discussion. ​

A contribution by Jennifer Dannheim​, Alfred Wegener Institute, addresses the lack of understanding and research on the cause-effect-relationships by the implementation of artificial structures in benthic systems. With her co-authors, she identifies knowledge gaps on how marine renewable energy installations affect the ecosystem functioning and services of the benthic system. "In particular", she says, "these are about (a) hydrodynamic changes possibly resulting in altered primary production with potential consequences for filter feeders, (b) the introduction and range expansion of non-native species (through stepping stone effects) and, (c) noise and vibration effects on benthic organisms. Our results further provide evidence that benthic sensitivity to offshore renewable effects is higher than previously indicated".

Dannheim concludes that, "Knowledge and understanding of the cause-effect relationship and how the benthos is affected by the implementation of man-made structures is a prerequisite to the development of sustainable management plans in order to know which effects may disappear or may last on the benthos by decommissioning"​.

INSITES

The timely publication contributes to the scientific knowledge base on the impacts of man-made structures on marine ecosystems with the specific aim to generate new evidence-based debate over decommissioning. Richard Heard is Programme Director of INSITE (INfluence of man-made Structures In The Ecosystem) which specifically looks at understanding the influence of man-made structures on the North Sea ecosystem. With INSITE phase I complete, Heard states that, “The publication of this ICES Journal of Marine Science themed set is perfectly timed to showcase some of the INSITE phase I research and development and prepare us for INSITE phase II in the summer".

Maturing science

Birchenough and Degraer are thrill​​ed to have been involved in producing this contribution and thank all the enthusiastic authors for their support. Their introduction provides the reader with a comprehensive overview and is a good starting point to dive into the topic.

Degraer concludes, “There is an urgent need for a robust understanding of the effects of artificial hard substrate and the consequences of its removal (e.g. through decommissioning) to marine biodiversity. The science needs to move at a faster pace and has yet to develop to maturity". ​

​Read Decommissioned offshore man-made installations in ICES Journal of Marine Science.