Tjuvholmen's Green Gift to Oslo

8. April 2025

Did you know that between 2007 and 2009, around 1,557 mussel ropes were installed in the quay plates and approximately 359 cleaning reefs were placed underneath as a gift to Oslo and a boost for the Inner Oslofjord? With potentially thousands of mussels per rope, the mussel ropes in the Tjuvholmen project now function as an effective, natural purification system in the heart of the city.

As a gift to Oslo and a boost for the Inner Oslofjord, an ambitious environmental initiative was launched at Tjuvholmen between 2007 and 2009. With the goal of increasing biodiversity and the amount of marine life in the fjord, the project was carried out in collaboration between Tjuvholmen KS, the Norwegian Institute for Water Research (NIVA), and Fiskehus AS.

The project included the installation of 1,557 mussel ropes and 359 cleaning reefs beneath the piers at Holmen, along with 200 artificial reefs placed along Tjuvholmen’s west side. The artificial reefs – designed to attract fish and lobster – were carefully positioned to provide shelter and breeding grounds for various marine species. The mussel ropes functioned as nutrient-rich hanging habitats, while the cleaning reefs attracted filter-feeding organisms such as mussels and sea squirts.

Did you know?

🔹 Mussels are nature’s own water filters. One adult mussel filters over 100 liters of water per day and can live for more than 20 years.

🔹 Mussels can absorb microplastics. They take up microplastics, bind them, and leave behind less harmful waste that sinks to the fjord floor.

🔹 Mussels help reduce bacteria in the water. High levels of bacteria are one of the most common reasons for swimming bans in the inner harbor. Mussels absorb and reduce these bacteria.

🔹 Mussels combat over-fertilization. Excess nutrients are a major issue in the Oslofjord, fueling algal blooms that can disrupt the ecosystem. Mussels feed on this phytoplankton, acting as a natural filtration system for nutrient pollution.

Image is AI-generated.

Sources:

https://www.science.org/content/article/mussel-poop-may-help-clear-oceans-microplastics (https://www.science.org/content/article/mussel-poop-may-help-clear-oceans-microplastics)
https://www.scirp.org/journal/paperinformation?paperid=87114 (https://www.scirp.org/journal/paperinformation?paperid=87114)
https://www.hi.no/hi/nyheter/2024/mai/her-er-fem-hovedgrunner-til-at-oslofjorden-er-i-kjelleren (https://www.hi.no/hi/nyheter/2024/mai/her-er-fem-hovedgrunner-til-at-oslofjorden-er-i-kjelleren)
https://www.hi.no/hi/temasider/arter/blaskjell (https://www.hi.no/hi/temasider/arter/blaskjell)

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