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



…. or my 25th Anniversary cruise!

29 January 2021
Blog by Katrin Linse

Early May 1996 I stood on the wooden pier of Puerto Williams, the southernmost city of South America, waiting for the rigid inflatable boat of RV Polarstern to pick us up. We were joining the ship to sample the seafloor animals living on the South American shelf and deep-sea slope of the Drake Passage to compare them with those living in Antarctica. I was an undergrad student, send to deploy a newly designed epibenthic sledge (EBS) with an epi-benthic and a supra-benthic sampler collecting animals living on the seafloor as well as swimming about one meter above it. My aim was to collect samples for my upcoming PhD project.

Katrin Linse in front of the two epibenthic sledges deployed during IceDivA. Photo Mia Schumacher

And now, almost 25 years to the day, I am standing on RV Sonne, 500 km north of Madeira and am waiting to send our double-sampler EBS BERTA to the Abyss (Figure 1). The aim is to collect the small-sized invertebrate animals (e.g. shrimps, worms, clams, brittle stars and their friends) from 4170 m depth so we, the marine biologists and taxonomic experts on board and back on land, can study their biodiversity and distribution patterns. You could call us the modern day Linneaus’ or Darwins, as our research starts with studying the animals we collect in detail; identifying their scientific names or if newly discovered, describing them and giving them scientific names, before we use their morphological and molecular characteristics to analyse their evolutionary relationships. The taxonomic group I am most familiar with are the bivalves, the two-valves seashells that include clams, cockles, and mussels, and especially those from the Antarctic and the deep sea.  Over the last 25 years colleagues of mine and I have collected marine seafloor animals by epibenthic sledges throughout Atlantic Ocean, the from Iceland via the tropic to the southernmost Weddell Sea in Antarctica. This enables me now to evaluate taxa, like the pictured Cuspidariidae (Figure 2), a group of carnivorous bivalves, for their distribution ranges, phylogenetic relationships, and postulate what resilience they might have for climate change.

So far I have deployed our EBSs six times to ocean depth of 4900 m to 5500 m depth and I am hoping for another four deployments before we have to end our biological field science and steam back to Emden. And while each mudding sample coming up might only have a few litres of volume, these can include hundreds to thousands of the small animals my colleagues and I want to study. The first expressions of joy you can hear when we sift the samples over 300µm sieves and see a faint movement of an isopod, this is a marine woodlouse, or worm, or the shimmering shell of a bivalve.

Deep-sea bivalves of the family Cuspidariidae from Iceland via the tropics to the Antarctic. Photos courtesy Nicole Gatzemeier, Katrin Linse, Anne Helene Tandberg.

This IceDivA expedition or SO280, following RV Sonne’s numerical expedition order, is very special to me, not only because it marks 25 years for me of joining ship-borne expeditions, but also being allowed to enrol during the current pandemic. As national and international travel is heavily restricted and many nations are in lockdown, we on board, after quarantine and multiple tests prior to and social distancing at the start of the expedition, are now allowed to work together like in the past. And working in temperate and non-polar waters is still exceptional for me. Being employed at the British Antarctic Survey, I am more familiar with an ocean covered in sea ice (Figure 3) than with water and air temperatures above 15°C. And I thought travelling to the North Atlantic in January would be mean cold days of working on a windy deck. Therefore, I packed my Antarctic, padded, extra warm, waterproof overall, to stay warm and dry. How did I fail. Luckily, RV Sonne’s store sells branded T-shirts to stop me over heating while at work.

My only other warm-water expedition has been the scientific Maiden voyage of RV Sonne in December 2014 to January 2015. Coming back on board six years later and seeing familiar faces from the ship’s crew again is another pleasant point of this expedition. Knowing you are in great hands that will enable you to collect your research samples 24/7 but also telling you when your scientist’s ideas/plans are technically or weather-dependent unachievable.


The research vessels RRS James Clark Ross and RV Polarstern meeting 2018 in the sea ice-covered Southern Ocean. Photo courtesy Michael Gischler