Impact story

Halfweg gas platform: leave the foundation in place?

Petrogas Netherlands is considering leaving part of the foundation of the decommissioned Halfweg gas platform in the North Sea. What are the consequences for marine life if the concrete gravity-based structure that formed the foundation for the installation is removed? Wageningen Marine Research is conducting the research.

The impact that the removal of the remainder of the platform will have on the ecosystem forms part of the considerations that Petrogas Netherlands includes in its internal decision-making. To this end they have asked marine ecologist Dr. Joop Coolen to take stock of the biodiversity that has been created over the years around the concrete structure measuring 26 metres wide, 28 metres long, and 6 metres high.

From a biodiversity point of view, there is no reason to remove the artificial reef.
Joop Coolen, researcher at Wageningen Marine Research

39 samples in four dives

In the summer of 2019, Coolen and a diving team visited the foundation of the Halfweg platform on the North Sea. With a team of six divers he completed four dives to a depth of approximately 25 metres to take samples of life on the structure from 39 different locations.

They used an airlift sampler (something like an underwater vacuum) to scrape growth from the surface, and it was collected in small bags. On board of the research vessel, the samples were then cleaned and stored in jars with ethanol. As a final step, all samples were counted, weighed, measured, and identified in the Wageningen Marine Research laboratory.

Biomass twelve times larger

The analysis of the samples resulted in the discovery of 65 different species and they were compared to other samples from reefs in the North Sea. 15 of the 65 species had not been found on other installations before, and two were new marine species for the Netherlands. The Halfweg samples were also compared to information about biodiversity in a reference area near the Halfweg platform which consists of sandy seabed. In addition to the number of species, the total amount of marine biomass per square metre was studied. The research shows that the benthic biomass present on the platform is twelve times greater than the biomass in the reference area with sandy seabed.

Joop Coolen conducts research into the biodiversity on artificial reefs in the North Sea. This includes oil and gas platforms, wind farms, and shipwrecks, as well as solar panel islands and possibly wave power plants in the future. These areas will develop into artificial reefs with abundant biodiversity. They will become part of the ecosystem.

Joop recently published his scientific publication in Journal of Sea Research relating to the assignment (fieldwork was completed in 2019) for Petrogas Netherlands (who are considering leaving part of the foundation of the dismantled Halfweg gas platform on the seabed). The company commissioned Wageningen University & Research to conduct research into the sea life on the concrete container, measuring 25 by 25 meters, that formed the foundation for the installation.

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