Skagerrak
Reefs

Apart from sandy and stony reefs, extensive cold water coral reefs, mostly of Lophelia, are growing in Skagerrak. The Säcken Reef in the Swedish marine protection of Koster Fjord is an ancient cold water coral reef and the only known coral reef in the country. The Tisler Reef in the Norwegian marine protection of Ytre Hvaler National Park is the largest known coral reef in Europe. Lophelia reefs are also present in the Norwegian trench and they are known from the shallow waters of many Norwegian fjords.

Skagerrak also holds a number of rare bubble reefs; biological reefs formed around cold seeps of geological carbohydrate outgassings, usually methane. These rare habitats are mostly known from the Danish waters of Skagerrak west of Hirtshals, but more might be discovered in future surveys. Bubbly reefs are very rare in Europe and supports a very varied ecosystem.

With the centuries-long heavy international seatraffic of Skagerrak, the seabed also holds an abundance of shipwrecks. Wrecks on shallow waters, provides a firm anchoring for several corals and polyps and explored wrecks have been revealed to support Dead Man's Fingers corals, Brittle stars and large wolffish. A 2020 seafloor mapping project around Jammerbugten in Skaggerak, ran by Danish explorer Klaus Thymann, found evidence of much greater biodiversity in a range seafloor habitats previously thought to be sandy with a low density of wildlife. Dead Man’s Fingers corals were again among the species documented for the first time in these coastal habitats.
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