Trondheimsfjorden in Middle Norway is unique in the world because deep-water corals (Lophelia reefs) grow so shallow in this fjord that they come in divers reach.
Lophelia corals do not live in symbiosis with algae and need no sun light in contrast to the related species we know from the tropical seas. They mostly live in depths between 200 and 2000 meters at 4 to 12 oC. Reefs are common in the eastern North Atlantic, and occur at least in the western North Atlantic and off central Africa. There are also other non-reef records of Lophelia in the Atlantic, and in Indian and Pacific oceans. The reefs can build up to 35 meters height and form rich habitats for many deep-water species. A study of Lophelia pertusa reefs off the Faeroes indicated that the diversity of Lophelia reefs is comparable to that of some tropical corals.
Lophelia reefs are quite abundant along the Norwegian coasts at depths between 200 and 2000 meters. Unfortunately about half of these reefs are severely damaged because of bottom trawling by fisherman, bottom- trawling, mineral extraction, and oil and gas exploration. But the Norwegian government took some serious measurements to protect these reefs. Norwegian fisherman are cooperating well, they realize that fish concentrations are higher within the reef areas than outside.
One place in the Trondheimsfjorden are known for its Lophelia reef and associated species. This place is declared a marine protected area: the Selligrunnen reef near the island Tautra. Another place where you can find reefs is Skarnsundelet, a narrow connection between the Trondheimsfjorden and the Beitstadfjorden but here the reefs are only a few meter in diameter. Why do they grow in shallow water in these places forming the worlds shallowest Lophelia reefs? It is stated that the connection with deep oceanic water, the strong currents and good feeding conditions are favourable for deep-water corals.
But the most determining factor seems to be the sediment rich freshwater from the rivers which floats on the saltwater and stops the light reaching deeper waters. The importance of these conditions can be derived from a similar example, the Sunken Valley in Tasmania. Here a 3-6m thick surface layer of fresh water which is stained dark brown by tannins blocks the sunlight and causes the clear salt water below to be very dark. The salt water with light conditions comparable to 400m depth is also home to several species from deeper waters.
Other impressing tree-like structures that can be seen on these places are deep-water gorgonian corals. One species is the pink-red colored Paragorgia arborea (bubblegum gorgonian coral) that usually lives between 200m and 600m depth. Anther is the orange-red colored Paramuricea placomus (gorgonian fan) that usually also lives at great depth. And the orange deep-water gorgonian Primnoa resedaeformis (rice grain gorgonian coral) can be found up to 32 meter depth. Also the corals form a nice habitat for many other deep-sea species and so this is a perfect place to many more species normally only found in deeper water.
Diving on these reefs can be very challenging and is not recommended for beginners. The water is cold and dark and dives have to be planed exactly. Even then currents are very unpredictable.
It is not the intention of this site to write about a coast the author never visited. But this place is so unique I wanted to add it to the site.