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Lophelia-corals on legs of a platform.
Photo: Erling Svensen
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“Floating” coral reefs

Corals in a multitude of shades of white, pink and orange shone towards the sea surface from the legs of a platform that was recently dragged into Hardangerfjorden from the North Sea. The most colourful coral was the reef-building Lophelia pertusa, but a far rarer visitor was also discovered. The non-branching deep-water coral Desmophyllum cristagalli has only been found in Norway on two previous occasions.

By Beate Hoddevik Sunnset

The Lophelia colonies, which are not unusual on platform legs, are up to approximately 1.5 m in diameter. The platform has been in the sea for thirty years, which means that the coral’s annual growth rate is at least 2.5 cm. According to researcher Pål Buhl-Mortensen, that is the normal maximum growth rate for Lophelia corals. Previously it was widely believed that they could only grow 6-7 mm a year, but that is actually the average rate. The maximum growth rate is much faster, as new polyps initially grow rapidly until they grow new branches. Polyps that have produced branches remain alive, but their growth rate falls to just a few millimetres a year.

Lophelia corals on platform legs.
Photo: Erling Svensen
The Lophelia colonies are up to approximately 1.5 m in diameter.

No natural coral reefs in the North Sea

There are no natural coral reefs in the central part of the North Sea. Corals reproduce by releasing free-floating larvae into the sea, which drift with the currents until they find a suitable place to attach themselves. The natural habitat of the Lophelia coral is stony bottoms. The fact that coral reefs have been found on platform legs demonstrates that there are coral larvae in the North Sea. It is likely that the absence of natural coral reefs in the area is due to the lack of a stony sea bottom.

Corals found in this way are interesting from a research point of view, and may help us to understand the genetics, growth rates and dispersal of corals, to mention just a few areas.


Lophelia corals on platform legs.
Photo: Erling Svensen


The pictures of the corals were taken in Hardangerfjorden in conjunction with the EPIGRAPH research programme, which is looking at coastal areas and fjords. Previously the project has documented the existence of coral reefs in Hardangerfjorden itself, taking photos of them with a remote-control camera.