Coral reefs

Deep-water coral reefs have many similarities with coral reefs in shallow, warm waters. Amongst other things, they are made of stony corals, and are home to incredibly rich biodiversity. In Norway, the reefs are formed by the coral species Lophelia pertusa. This coral was first discovered in the mid-18th century by Bishop Johan Ernst Gunnerus. Carl von Linné described the species in 1758, but until the 19th century it was not realised that it actually forms reefs. In fact, only once the oil industry started using ROVs (remotely operated vehicles, i.e. mini-submarines) and other advanced equipment to explore the sea bottom did the study of coral reefs as an ecosystem really take off. Reports that significant damage was being done to reefs by bottom trawling also played an important role in helping to raise their profile.

Live white Lophelia.
Live white Lophelia.

In 1997, The Institute of Marine Research started monitoring areas where this kind of damage had been reported, and the pictures it took of the sea floor largely confirmed the concerns of the fishermen. The Institute’s survey of damaged and intact reefs has been used to establish conservation areas for coral reefs. The first such area was Sularevet, and subsequently a number of other areas have been protected using both fisheries and conservation legislation.

Around 600 coral reefs have been documented and mapped, but we know that far more than that remain to be documented. If we take into account all of the evidence from multibeam echo sounding, the figure is probably closer to 6,000. MAREANO’s map service now has up-to-date maps that show all of the known coral reefs in Norwegian waters, as well as marking coral reef conservation areas. The database is based on scientific studies, including The Institute of Marine Research’s projects, such as MAREANO, and on information provided by fishermen and the oil industry.

It contains over 600 records, including point data (reef locations), reef areas where there are several reefs close together and conservation areas for coral reefs. Reef areas can contain more than one thousand individual coral reefs, as in the case of the Træna area.

The maps show three categories of coral colonies:

Category 1

Coral areas where bottom trawling is prohibited under Norwegian law (conservation areas).
These named reefs are documented through high-resolution sea floor maps based on multibeam echo sounding and video observations. The one exception is Iverryggen, for which we do not yet have a high-resolution sea floor map.

Bottom trawling is prohibited in the following areas:

  • Tisler (Østfold)
  • Fjellknausene (Østfold)
  •  Sularevet (off Nord-Trøndelag)
  • Iverryggen (off Nord-Trøndelag)
  • Røstrevet (off Nordland)

In addition to these, a coral reef at Tautraryggen in Trondheimsfjorden is also protected (Selligrunnen).

Category 2

Coral areas that do not have special protection against bottom trawling, but that are well documented. These reefs are named, and many of them are also documented with high-resolution sea floor maps. The exceptions to this are the areas along Storegga and Aktivneset–Storneset, which are generally not covered by good maps.
Many of these coral colonies have been documented thanks to information provided by fishermen, which has then been confirmed by video surveys carried out by The Institute of Marine Research (e.g. as part of MAREANO) and oil companies. The maps do not show information from fishermen that has not yet been confirmed by video surveys or by some other method.

The areas in this category are:

  • Store Fjellknausene (Østfold)
  • Søndre Søster (Østfold)
  • Aktivneset (off Møre og Romsdal)
  • Korallneset (off Møre og Romsdal)
  • Breisunddypet (off Møre og Romsdal)
  • Sørmannsneset (off Møre og Romsdal)
  • Skallen (off Møre og Romsdal)
  • Storneset (off Møre og Romsdal)
  • Bjørnsundet (Møre og Romsdal)
  • Gosen (Møre og Romsdal)
  • Hesteskoen (off Nordland)
  • Træna (off Nordland)
  • Hola (off Vesterålen)
  • Fugløyrevet (Troms)
  • Lopphavet (Finnmark)
  • Stjernsundet (Finnmark)
  • Korallen (Finnmark)

Category 3

Coral reefs that are marked on the maps as unnamed black spots.

These reefs have been documented with high-resolution maps or through video surveys. Information sources include The Institute of Marine Research, from projects such as MAREANO, and oil companies.

Although reefs in Norwegian fjords were discovered first, they have been studied less than the reefs on the continental shelf. This is because of the clear threat posed by bottom trawling and pipes laid by the oil industry.
However, it now appears that coral reefs in fjords can also come into conflict with a number of human activities.

In 2007, the MAREANO project mapped the coral reefs in the Hola area off Vesterålen. Here there are approximately 330 coral reefs that are elongated in the direction of the current, and which are only alive on the side facing the current. It appears that where there is a prevailing current, the reefs grow towards the current, as that is where their food comes from. As a result, the coral reefs have a “tail”, which can be several metres high, and the oldest parts of which are around 6,000 years old.

Coral reefs as an ecosystem

Coral reefs grow slowly, and can survive for thousands of years. The oldest coral reefs in Norway are around 9,000 years old. A wide variety of species find food and shelter amongst the branches of the corals, although these species are generally also found on other types of hard bottom not made of coral skeletons.

Species that are particularly adapted to life on Lophelia pertusa reefs include the coral worm (Eunice norvegica), the annelid worm Harmothoe oculinarum, the squat lobster (Munidopsis serricornis) and the parasitic foraminiferan Hyrrokkin sarcophaga. The latter is a large, single-cell animal which in Norwegian is called the “danish pastry animal”, a name given to it in the 1930s by Carl Dons, a pioneering scientist in the field of Lophelia, who also gave Norwegian names to many other animals that are common on the coral reefs.

Bubblegum coral and deepwater soft corals on dead Lophelia.
Bubblegum coral and deepwater soft corals on dead Lophelia.

The large number of species found on Lophelia corals can be explained by the great diversity of microhabitats (living environments). Not only does the coral skeleton contain lots of nooks and crannies and protective hollows, but there are also small areas of sediment deposits in amongst the coral branches, providing a suitable environment for both stationary filter-feeders and burrowing sediment-eaters. The great majority of the species on the reefs live by filtering organic particles out of the water. These particles drift with the currents, so it is no coincidence that coral reefs are found in places where those currents are relatively strong. The corals themselves are dependent on a good supply of edible organic particles.

As coral reefs are large, complex structures situated in nutrient-rich areas, they also make a good home for many different species of fish. Particularly common species include the Norwegian redfish, common redfish and tusk. The redfish find food in the waters just above the reef, but when the current is too strong, they shelter down amongst the coral branches. The tusk likes the small caves that are common in between the coral colonies. It is clear that the reefs offer lots of good hiding places for small fish, and that they provide food for a wide variety of species, but we know little about their role in spawning and in helping juveniles to survive.