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MAREANO has completed the mapping at Troms III outside of Arnøya, located in Lopphavet in Troms, and is now steaming southwards to Nordland VI, at the southern tip of Lofoten.
By Lis Lindal Jørgensen (IMR), Leif Rise og Valerie Bellec (NGU). We like to thank Maria Kaurin, guest and student on the MAREANO 2010112 survey for her English translating of the text.
Figure 1. "G.O. Sars" leaving Troms III where we have mapped the marine life and sea bottom north of Arnøya (can be seen in the background) in Troms. We are now continuing on to Nordland VI.
During the past few days we have visited a large shallow area, Alangstaren, north of Arnøya. Alangstaren (figure 2), a familiar name to local fishermen, is a part of this shallow area which is situated at the western edge of Lopphavet. The rocks exposed on the seafloor here are old, and made up by the same hard type as we find on the mainland and nearby islands. It is therefore more difficult to erode these rocks, than the softer sedimentary rocks occurring at deeper water both east and west of Alangstaren. Under periods with lower sea level large waves eroded the rocks, and several times the area experienced the wear and tear of glaciers. Imaging that we travel one million years back in time, then Alangstaren was probably the westernmost island in Lopphavet.
Figure 2. Lopphavet, with shallow areas (brown colour) and deep areas (purple).
At Alangstaren we conducted a video transect which started at 27 m depth. The kelp forest reached down to 37 m depth. The leaves of the kelp were covered in white spots consisting of the moss like animals known as Bryozoa. These colonies grow in all directions and as a result of this end up with a more or less circular appearance (figure 3).
Figure 3. Kelp forest found at 34 meters in the shallow areas right north of Arnøya in Troms. The white spots seen on the kelp leaves are colonies of the moss like animals known as bryozoans.
On the sea floor between the kelp leaves we found common sea stars (Asterias rubens) (figure 4), bushy bryozoans, worms living in calcareous tubes (Sepulidae polychaeta), and red algae.
Figure 4. Common sea star (Asterias rubens).
We also encountered spiders in the kelp forest (figure 5). However, these spiders are not like the ones we know from terrestrial systems, but sea spiders (Pycnogonida). The sea spider mainly consists of legs. The main body is so small that several of the organs are actually placed in the legs. The sea spiders are usually between 1-10 mm long, but in deeper water some individuals can attain a body length of up to 6 cm and a distance of up to 75 cm between the legs. Many sea spiders are predators that live of bryozoans, hydroids, soft corals, sea anemones and sponges. The kelp forest can therefore provide many food sources for the sea spider.
Figure 5. A Sea spider (Pycnogonida) is climbing around between kelp and seaweed. It is probably hunting for food. Some species of sea spiders eat, amongst others, bryozoans seen as white dotes on the kelp. The sea spider uses its trunk like proboscis to suck up its prey from the colony of bryozoans.
Just south of this shallow area, during our last video transect at Troms III, we discovered a sea bottom covered by several hundred brittle stars per square meter (figure 6). It is not highly unusual to find enormous densities (up to 10,000 individuals per square meter) of, among others, Ophiothrix fragilis at larger depths.
Figure 6. Hundreds of brittle stars were registered north of Arnøya in Troms. The brittle stars formed a dense aggregation, with individuals just not overlapping each other. In the middle of the picture a burrow can be spotted. This is probably the living quarters of an animal, maybe the home of a Squat lobster (Munida).
This transect showed a low diversity of animals. One can therefore speculate on what kept all the brittle stars alive. Brittle stars are a diverse animal group which can be predators, scavengers, detrivores or filtrate food particles out of the water current. While studying the species at close range by zooming in with the camera, we saw a crustacean swim straight into the arm of a brittle star. The brittle star reacted instantly and captured the crustacean with its arm and pulled it under its central disc where its mouth is located. One moment later the brittle star had entered the same position we often sea in common sea stars, the prey was held in place under the oral disc by all five arms while the mouth was used for ingesting the prey (figure 7). This may be the first time this behaviour is captured on film for the brittle star species Ophiothrix fragilis.
Figure 7. The brittle star seen the centrally in the upper part of the photo to the left has just captured a small crustacean. With its five arms it has grabbed a hold of its prey and drawn it in under the central disc where the mouth is located.
The fact that one of the brittle stars had captured a prey was immediately noticed by the neighbouring individuals. They drew closer while touching the lucky hunter with their arms. A short while later the hunter was completely covered by the other brittle stars (figure 8).
Figure 8. After a brittle star has captured a prey, in this case a small crustacean, other brittle stars of the same species are climbing onto the lucky hunter. This can probably be explained by the fact that the other brittle star has picked up the scent of food and is drawn towards the source of this smell.
Stone corals (figure 9) and gorgonian corals (figure 10) were also found at the same transect. The deep sea coral reefs found in our waters has a lot in common with the coral reefs in shallow water in warmer areas. They are made up of stone corals and is the home to an amazingly variety of animals. In Norway the reefs are formed by the species Lophelia pertusa. It is possible to read a lot more about corals and coral findings at MAREANOs website.
Figure 9. Lophelia-reef outside Arnøya. The reef shell Acesta can be spotted between the corals. Lophelia pertusa is a stone coral (Scleractinia) belonging to the Hexacorallia. The picture is taken at speed while the camera was gliding through the area. The laser, used for measuring sizes of different organisms and features, is therefore in use. The light from the laser is visible as two red dots in the photo. The distance between the dots is 10 cm.
Figure 10. The picture is showing a colony of Paragorgia arborea (sea tree) which is a gorgonian coral. The gorgonian corals belong to the Octocorallia. Lophelia pertusa (stone coral) and the reef shell Acesta excavate can also be seen in this photo along with large quantities of brittle stars. The sea anemone Protanthea simplex can also be spotted in the top right of the picture.