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