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October 20, 2025

Dive into the incredible Grand Canyon of the Kattegat

 

(Excerpt of the original article in Danish, written by Dyrenes Beskyttelse).

Quite close to the coast east of Anholt lies an area which with large mountains and deep river valleys that reminds us of an underwater version of the Grand Canyon, but with equally rich nature.

With depths up to 130 meters, colourful stone reefs, strong currents and a varying salt content in the water, the area creates the perfect conditions for life. That’s why the area also offers a seabed with kelp forests, beautiful corals and many different distinctive animal species. Several of them have not previously been seen in Denmark.

The area dates all the way back to the Ice Age and is called the canyon system. As a result of the Fisheries Agreement from July, it will be protected from destructive trawl fishing. This brings great excitement to Nicolaj Lindeborgh, who is a marine biologist at Dyrenes Beskyttelse.

 “There is no other place in Danish waters where so many different types of nature are gathered in one place – and the more types of nature, the more animals, the more biodiversity. It’s a celebration,” he says.

Oceana is one of the first to have investigated the deep parts of the area. This has only been possible with the help of very special technology. Among other things, the use of a Remotely Operated Vehicle (ROV), to dive underwater into the Kattegat canyon system.

Previous studies found 42 different seaweed plants and 179 different animal species. Only small areas were studied – the species richness is probably much greater. Oceana has managed to get good images of many of the species. “Some of the videos that Oceana has recorded are unique – this is the first time I have seen films of marine sponge communities, horse mussels and haplogroup communities from Danish sea areas”.

When Oceana goes out to sea to explore ocean depths, we find marine life and habitats in need of protection, often unique ecosystems, sometimes rare species and even ones unknown to science! What we found in Denmark is a good case in point. Better knowledge and data is essential to advance marine protection” said Nicolas Fournier, campaign director at Oceana in Europe.

Fact box: Kattegat’s Grand Canyon

  • The area is located centrally in the Kattegat and stretches from Anholt in the south and about 50 km towards Læsø in the north.
  • The area proposed to be protected from bottom trawling is about 650 square kilometers, corresponding to 0.5% of the Danish marine area.
  • The area is very varied; there are large stone reefs and deep trenches. Depth varies between 15–130 meters. A lot of water flows through the Kattegat – about 21,700 cubic kilometers of water per year, and the current speed in the trenches is among the strongest found in Danish waters.

Dive in and see the crown jewels of the Kattegat

The Sea Feather

The colourful pipe cleaners of the sea

Do we have corals in Denmark?
Yes, and even a handful of different species. The Sea Feather (Søfjeren) and the Sea Pen (Søpennen) are two species that both live in deep, soft muddy seabeds. Unlike the corals that form coral reefs, these corals are soft. When talking about a Sea Feather or a Sea Pen, it’s actually a colony made up of many animals, so-called polyps, that together form a single organism.

Sea Feathers are sensitive to trawl fishing. In the protected area, there is currently intense trawl fishing for Norway lobster (jomfruhummer) in almost all places where soft seabeds are found. When trawl fishing soon comes to an end, it is expected that many sea feathers will once again appear on the seabed.

Dead Man’s Hand

The coral with the eerie name

Like the Sea Feather and Sea Pen, the Dead Man’s Hand is a soft coral, and just like the other two, each Dead Man’s Hand consists of a colony of polyps—meaning multiple animals.

Dead Man’s Hand corals attach themselves to hard surfaces such as rocks and mussels. Occasionally, they form impressive growths across large areas, reaching up to 20 cm in height.

Haploops

Return of the Haploops

The Haploops Community
It might sound like something out of a Star Wars movie, but it’s actually a unique ecosystem named after two species of amphipods: the Common Haploops and the Fine Haploops. These creatures build small homes around themselves using cemented mud.

Around the 1900s, the Kattegat was full of Haploops—to such an extent that a quarter of the muddy areas were dominated by these animals. Today, they are almost gone. Bottom trawling is likely the reason they have nearly disappeared from the Kattegat and are now considered threatened.

Oceana has found Haploops both in the area planned for protection and further north in the Kattegat Canyon—this shows that Haploops are still present in the Kattegat and gives hope that they can reestablish their remarkable community across larger areas once again.