By Pål Buhl-Mortensen og Beate Hoddevik Sunnset
What all of these biotopes have in common is that their characteristic organisms are relatively large and delicate. In areas where bottom trawling takes place, these biotopes can easily be destroyed. Several of them also have a great diversity of associated fauna.Bubblegum coral, Paragorgia arborea and red tree coral, Primnoa resedaeformis are the most common sea fans in hard-bottom coral forests in Norwegian waters.
The various biotopes have habitat-forming species that are characteristic of the area. These species, which typically live in deep waters (>100 m) and form biotopes far below the sea surface, have in the past received little attention.
The Oslo/Paris convention (OSPAR) has compiled a list of marine habitats that threatened and/or declining. This list includes deep-water sponge communities, coral reefs, coral gardens and sea pens and burrowing megafauna, all of which are found on the sea bottom off Norway. Several of these habitats are so loosely defined that they can be split into several biotopes. This applies to coral gardens, for instance, which in Norway can be split into cauliflower coral meadows, soft-bottom coral forests and hard-bottom coral forests. We have therefore given new names to several vulnerable biotopes mapped by MAREANO:
- Umbellula (deep-sea pen) populations
- Radicipes sp. (a type of coral garden that we believe should be classified under the biotope “soft-bottom coral forests”)
- Glass sponge populations
The biotopes found by the MAREANO project are:
- Sponge communities: A variety of large sponge species (Geodia spp., Aplysilla sulfurea, Stryphnus ponderosus and Steletta sp.). For Tromsøflaket and Eggakanten, MAREANO has demonstrated that the sponges in this kind of biotope create a sea bottom that is a mixture of mud and sponge spicules. The sponge communities shown on the map do not include hard-bottom sponge communities, which are home to more species, but which usually have a lower density of colonies.
- Glass sponge populations: In deep water, several species of glass sponge are found in relatively high colony densities. We have not yet determined the species of several of the sponges observed by the MAREANO project. In order to do so reliably, in most cases it is necessary to look at the microscopic spicules. One of the most common species of glass sponge is the Caulophacus arcticus, which is generally found on hard sea bottoms on the lower part of the continental slope.
- Umbellula populations: In patches the deep-sea pen Umbellula encrinus is found in relatively great densities from half way down the continental slope (approximately 800 metres below sea level) and deeper. This large sea pen can reach a height of more than two metres. The Umbellula populations can be viewed as the deep sea equivalent of the shallower biotope “sea pens and burrowing megafauna”. There are often high densities of tube-building amphipods (a group of crustaceans) in areas with Umbellula.
- Sea pen bottoms: In OSPAR’s list this biotope is called “sea-pens and burrowing megafauna”. In the area covered by the MAREANO project this biotope is mainly home to the sea pens Funiculina quadrangularis, Virgularia mirabilis, Pennatula phosforea and Kophobelemnon stelliferum. The Norway lobster (Nephrops norvegicus), squat lobster (Munida sarsi) and sea cucumber (Stichopus tremulus) are also common in this biotope.
- Soft-bottom coral forests: Radicipes had not been found in Norway until MAREANO found relatively dense concentrations of this sea whip in the area known as the Bjørnøya slide. Like the bamboo coral Isidella lofotensis, the species lives on sandy mud bottoms. OSPAR refers to all coral communities with a certain density of colonies as “coral gardens”. Coral gardens can be found both on soft and hard sea bottoms, and consist of a large number of very different species and groups of corals. It is therefore appropriate to split this loosely defined habitat into “soft-bottom coral forests” (Isidella and Radicipes) and “hard bottom coral forests” (Paragorgia arborea, Primnoa resedaeformis, Paramuricea placomus and Swiftia spp.).
- Hard-bottom coral forests: Where currents are strong and the sea bottom is hard, there are sometimes sea fan populations that provide a habitat for fish, brittle stars and small crustaceans. The most common species of sea fans that make up hard-bottom coral forests are Paragorgia arborea, Primnoa resedaeformis, Paramuricea placomus and Swiftia spp. We do not have conclusive evidence that the Swiftia, which is more common in the relatively shallow waters off Rogaland, is also found in the MAREANO area. Although there is less biodiversity associated with the various sea fans that make up this biotope than with coral reefs, they nevertheless sustain a large number of individuals and a large number of host-specific species that are not found in other biotopes.
- Coral reefs: Lophelia pertusa is a stony coral which, over a long period of time, can build coral reefs. The Norwegian reefs that have been dated have been found to be 3000 to 9000 years old. Lophelia pertusa can form individual reefs or reef areas where the reefs are so close together that it is sometimes hard to distinguish them. At Hola, MAREANO has mapped a reef area consisting of around 330 individual reefs. MAREANO has also found previously undiscovered individual reefs at Malangsryggen and in the outer part of Malangsdypet. Other corals such as zigzag coral (Madrepora oculata), bubblegum coral and red tree coral help to increase the spatial habitat complexity and the biodiversity of the reefs.