Who lives at the bottom of the sea?

The deep sea floors are in constant darkness which means no plants can grow there. But that doesn’t mean it’s a place empty of life.

During the autumn of 2018 SGU (the Geological Survey of Sweden) and partner in the SEAmBTOH project, conducted a survey cruise in the archipelago of Haparanda to map the depths and substrate of the sea floor (i.e sand, mud or rocks). During their time there they also took samples to investigate what animals that lives in and on the bottom. And now we have the answer!

By a large “grabber” lowered down from the boat a piece of the bottom is scooped up. This large clump of “mud” then has to be carefully washed under a sieve which catches the small animals living in it. The animals are then transferred to jars for conservation. In the lab, and often under microscope, all the animals are identified and counted in number of species. They are also weighed to get the so called biomass of the living organisms within each sample.

Mud on a sieve. A person is washing it with a hose.
Washing away the mud from the sea floor to find the animals (bottom fauna) living in there. (Photo by Linnea Bergdahl, County Administrative Board of Norrbotten)

Saduria entomon

skorv, ishavsgråsugga or kilkki, as called in swedish and finnish

(Video by Linnea Bergdahl, County Administrative Board of Norrbotten)

The Saduria was found mainly in samples taken at the deeper locations, down to sea bottoms at 50 meters depth. Other animals found was mainly species from the group of bristle worms Marenzelleria, Oligochate (worms similar to the earth worms) and the shrimp-like Monoporeia affinis.

All these animals live buried down in the bottom where they feed of detritus (decaying organic material falling down to the bottom). The shrimp-like
Monoporeia affinis is sensitive to pollutions and can’t live on anoxic (oxygen depleted) bottoms.

Overall there were few species and few individuals found within the sampled area in the archipelago of Haparanda. And those that are there do an important job as feeding on decaying material and themselves turning into food for e.g. fish. Thereby they ensure energi and nutrients of the ecosystems of the sea keeps flowing.

Written by Linnea Bergdahl, County Administrative Board of Norrbotten


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