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Sediment secrets

  • 31 January 2021
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31 January 2021
Blog entry by Saskia Brix

The naked eye cannot see them, the trained eye has difficulty spotting them and when enlarged under a microscope they are ‘aliens’ – or should I better say the bumble bees, beetles and butterflies of the deep sea? What would the world be without insects? Well, did you know that marine crustaceans are siblings to insects – or – so to say – systematically, insects are a sister taxon to crustaceans!

This topic is connected to the term “biodiversity loss” on land and an urgent issue in terrestrial and marine biodiversity research. Who is talking/caring about these little, alien butterflies living down in 5500m depth, in a different cold, dark, wet world at high pressures in one of the most extreme environments on our blue planet? Here they are, the unseen sediment secrets: the little crustaceans, worms, snails and bivalves! Their beauty is revealed by sieving bucket-loads of mud collected by our gear after diving down attached to kilometre-long cables to the seafloor. Just think about the proportions: RV Sonne is 118m long compared to the water depth: the seafloor is reached by over 5 km length of a heavy, 18mm thick wire cable attached to the 0.18km long vessel!

Well, at first view, the seafloor looks like a pristine sandy beach, nothing is seen. Boring? Or boring?!? Caused by bioturbation below the sediment’s surface, you can spot Lebensspuren- and poo! Poo is everywhere and this means somebody lives there, consuming the seafloor for its nutrient content…

During the OFOS deployments, we spotted larger marine animals, the native deep-sea inhabitants, but also plastic litter of human origin on the seafloor. Even a pair of trousers made it down here. And from the ocean’s surface – some 500 miles from the nearest beach – we fished out a single flip-flop, being used as a raft by all different kind of crustaceans and snails.

Let the pictures speak and have a look:

1 ) Just imagine yourself swimming through honey! How must it feel for this little isopod fellow paddling actively across the deep-sea sediment? Munnopsid isopods swim using their posterior paddle legs while the four pairs of front legs are used for walking.  2) Tiny bivalves of 2 or 3 mm size connect with their byssos to anything they can get hold on in the sediment plains – even holothurhians are used as a taxi! 3)  This little 1 mm size comma shrimp or cumacean can only be found under the microscope between the single sand grains.  4) Fossil and recent, old and young  –  sharks were swimming around and loosing their teeth…. The story behind stays a riddle or comes alive in your own phantasy. 5) A salp colony glows in the dark. Never alone in the vast environment hanging around in the water column…

Animals seen from the OFOS: A)  Caridean shrimp; B) Brittle star; C) Liparid fish; D) Holothurian

Lebensspuren seen from OFOS: A) Animal track; B) Burrowing single animal; C) Starfish imprint; D) Burrowing animal colony

Litter seen from OFOS: A)  Plastic sheet; B) Brown glass bottle; C)  Trousers; D) Plastic sheet

 

 

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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 818123 (iAtlantic). This output reflects only the author’s view and the European Union cannot be held responsible for any use that may be  made of the information contained therein.