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P9260279

Den artsrike fangsten fra en bomtrål, der en rød solstjerne er midtpunktet.

Photo: Børge Holte / Havforskningsinstituttet

In the borderlands of the Polar Front

Expedition diary: After two weeks at sea, we have seen how benthic communities change with the seabed substrate and bottom-water temperature, from east to west on the Spitsbergen Bank. From the relatively deep mudflats in the south-east, to the rocky slopes in the north and further west towards Bear Island, we have observed large quantities of dead bivalve shells and shell fragments, as well as some high-Arctic benthic fauna. We are in the borderlands of the polar front.

So far, we have performed video surveys of around a hundred sea bottom locations, and at eight locations we have also collected samples of benthic fauna and sediments. 

Kart over seilingsruten under toktet
Map of the vessel’s route during the expedition’s first 2 weeks, showing locations of video surveys and seabed sampling. Map: Kjell Bakkeplass (IMR).

The differences in bottom types that we have observed result in the dominant benthic fauna varying from area to area, and the bottom-water temperature probably also plays a role. Whereas we measured the bottom-water temperature in the eastern part of the Spitsbergen Bank to be -1 °C, it was 3-4 °C further west on the bank. We are in the area known as the Polar Front, where cold Arctic waters from the north come up against the warmer Atlantic water from the west and south. 

Kjemiprøver pakker på lab ombord
Here Anders Fuglevik is preparing and packing sediment samples, which will be frozen and subsequently analysed for pollutants. Photo: Børge Holte (IMR)

The shells of dead bivalves, barnacles and snails cover large sections of the eastern areas of the Spitsbergen Bank. Some of the shells may be thousands of years old, and if you dig down 5-6 cm there are shell fragments that are probably up to 10,000 years old. But naturally we also observe the shells of animals that have died recently in the videos taken by the “Chimaera” video rig, which moves at 0.7 knots a few tens of centimetres above the sea floor. The accumulation of shell fragments is not unusual in shallow waters along the Norwegian coast, and they often form piles of shell sand similar to ones we have seen here on the Spitsbergen Bank. A high proportion of the shell fragments come from the “blunt gaper”, a species which we have caught alive in relatively shallow waters with our benthic trawl. The empty shells of Iceland scallops, alongside live scallops, can be seen scattered in varying quantities across large parts of the bank. 

Fjærestjerne på havbunnen
Echinoderms come in lots of different shapes. Starfish and sea urchins are probably the best-known ones, but sea lilies, like this large feather star called Heliometra glacialis, are adapted to life in strong currents. It uses its feather-like arms to snatch particles out of the water, and its long, jointed holdfast organs to hold on. The feather star can swim using its ten arms. Video-photo: Mareano/IMR

On the rocky substrate of the coldest, easternmost part of the bank, we observed large quantities of brittle stars, as well as the sea urchin Strongylocentrotus, which thrives in northerly waters. These are types of echinoderms, and many of them are familiar from cold, Arctic waters. However, the most typically high-Arctic species we observed in the benthic community was the sea lily Heliometra glacialis, which we found densely packed in the cold, eastern part of the Spitsbergen Bank. Although this sea lily bears no resemblance to either a brittle star or a sea urchin, it is also an echinoderm. Previously, the Mareano programme had only found significant amounts of Heliometra during our Arctic surveys in 2018-2019, to Kvitøyrenna east of Svalbard and in one of Europe’s northernmost fjords, Rijpfjorden on Nordaustlandet (Svalbard).

Nesledyr og mosdyr på havbunnen
We encounter many lovely “forests” of cnidarians and moss animals in areas with strong currents. Here we can see the red cnidarian Thuiaria breitfussi, which lives closely intertwined with the greyish-brown moss animal Eucratea loricata. There are many empty shells scattered across the sea floor, as well as patches of crust-shaped red algae. Down amidst the moss animals sits a small Arctic lyre crab, Hyas coarctatus. Video-photo: Mareano/IMR.

Further west on the Spitsbergen Bank, where there is some intrusion of warmer Atlantic waters, the benthic communities are more similar to the ones we know from rock and gravel substrates along the Norwegian coast. Typical species here included green sea urchins, nudibranchs, barnacles and hermit crabs. The latter, which we often see along the Norwegian coast, live in the shells of sea snails. Here, on the Spitsbergen Bank, it is clear that there is plenty of food for the hermit crabs to find between the rocks and barnacle shells. However, even on the sea floor there can be a shortage of space, and the principle of might is right often applies, leading to scuffles. 

The further west towards Bear Island we get, the stronger the bottom currents become, and many benthic animals cannot hold on in the powerful current. However, there are more orange-footed sea cucumbers here, which are equipped with suckers that give them a solid footing on firm rocks. 

 

In the same way as during Mareano surveys in 2017, we can see how the sea cucumbers provide shelter and a substrate for other organisms, creating a “sea cucumber bottom”, which also includes colonies of small cnidarians and moss animals.

 

Mareanos forskningsgrab settes ut
The crew of the research vessel G.O. Sars are doing an outstanding job for us. Here trawl master Even Rong deploys Mareano’s research grab. Photo: Børge Holte (IMR).

 

Contact

Børge Holte, 061119

Børge Holte

Havforskningsinstituttet
Forsker
916 30 856