Vulnerable biotopes mapped by MAREANO

Vulnerable biotopes in deep water (> ca 50 m) are characterised by large, fragile species of sponges, coral and sea pen. These are easily damaged by bottom touching fishing gear, especially bottom trawl, and they may also be vulnereable for increased concentrations of particles in the water, for exsample as a consequence of discharge of drilling mud. Trough analysis of results from MAREANO mapping five vulnerable biotopes are defined as described below.

The map that shows the distribution of these is based on modeling using ubundance data retrieved from video.

Soft bottom sponge communities (Demospongia): 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. Sponge spicules are small needle shaped skeleton structrures made of silica.

Sponge community
Sponge community (sponge spicule bottom) in the western part of Tromsøflaket, at a depth of approximately 250 metres. In this picture we see Geodia baretti and G. atlantica among other sponges.

Hard bottom sponge communities: Community of several medium sized sponges characterised by Phakellia spp., Axinella infundibulum, and Antho dichotoma. These occur on different hard sea bed substrates. This biotope is generally home to more species, but which usually have a lower density of colonies than soft bottom sponge community.

Typical hard bottom coral garden with Phakellia, and Axinella and several other species.

Glass sponge populations (Hexactinellida): 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.

Glass sponge
The glass sponge Caulophacus arcticus is common in deep waters off northern Norway. Here it has been photographed approximately 1,900 metres off Vesterålen.

Sea pen bottom: In OSPAR’s  list of threathened and/or declining habitats, 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.

The sea pen Kophobelemnon stelliferum is common in fjords and in the deep channels out on the continental shelf.

Umbellula populations: In patches the deep-sea pen Umbellula encrinus is found in relatively high 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 (Neohela) in areas with Umbellula.

Umbellula encrinus is a large sea pen only found on soft sea bottoms in deep water.

Soft-bottom coral forests: Two species of gorgonian corals (Radicipes gracilis and Isidella lofotensis) can form dense stands on sandy soft bottom in Norwegian waters. Radicipes had not been observed in Norway until MAREANO found relatively dense concentrations of this sea fan 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 entirely appropriate to split this loosely defined biotope into soft-bottom coral forests (Isidella and Radicipes) and “hard-bottom coral forests (Paragorgia arborea, Primnoa resedaeformis, Paramuricea placomus and Swiftia spp.).

In Norway, the sea fan Radicipes sp. is only found in the Bjørnøya slide in the northern part of the Eggakanten area (depth of 700-900 m). It forms “forests” on soft bottoms, and along with Isidella lofotensis it represents the biotope “soft-bottom coral forests”.

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. In the MAREANO area, the presence of Swiftia has not been confirmed, and it is more common in relatively shallow waters off Rogaland. 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.

Bubblegum coral and tree coral
Bubblegum coral, Paragorgia arborea and red tree coral, Primnoa resedaeformis are the most common sea fans in hard-bottom coral forests in Norwegian waters.

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. The coral reefs are habitat to a variety of other small and large species, ranging from fish to smaller invertebrates among which some only occur in the reefs.

Lophelia pertusa
Coral reefs are formed by the stony coral Lophelia pertusa. The reefs can reach heights of up to 35 metres, and can be over one kilometre long. Areas where there are many reefs close together are referred to as coral reef areas. Hola and Røstrevet are two examples of such areas. This picture was taken at Hola.