Most of the scientists on board are specialized in the study of marine life and every opportunity to see or sample what lives on the bottom of this ocean is taken very seriously in consideration. Luckily enough during the delicate task of providing fuel to the station, a few hours had to be spent in the vicinity of the ice shelf; this time was indeed needed for the people from Neumayer to reach our position. This was the perfect opportunity to use one of our sampling gear called “the Rauschert Dredge” (named after Dr. Martin Rauschert who designed this device) and see what creatures we could catch on the sea floor, 500 meters below the icy surface of the water.
The Rauschert Dredge is a rather small and simple gear, composed of a symmetrical metal frame that can land on the bottom of the sea on either of its sides and be pulled at the end of a cable for one hundred meters or so. Behind this frame, two nets (an inner one of 0,5 mm mesh and an outer one of strong 10 mm mesh to protect the first one) are attached to collect the animals that live on the surface of the sediment. After being dragged at slow speed for about fifteen minutes on the bottom of the sea, it took about half an hour for the dredge to reach the surface and then the working deck of the ship. This gave us the time to get ready with the sieves of different sizes and different buckets to put the most obvious or fragile animals of the catch in a safe place.
In a normal sampling station this dredge does not get a lot of attention;. many other gears bring a much bigger volume of material and therefore require many people to process it quickly on the working deck before the fine sorting of the catch is done in the laboratories.
This time was different: since the work of the scientists was temporarily on stand-by while the fuelling activities were taking place, everybody was available and curious about what we could get in what Dr Rauschert himself calls the “shopping bag”. Once on the working deck of the ship, the first thing that came out of the net was a 20 cm wide, intact and lively pycnogonid that attracted a lot of attention and enthusiasm from everyone around. Then the contents of the bag were carefully placed in a large bucket where larger and numerous holothurids, crinoids, ophiurids, asteroids and a few intact echinoids were collected.
When all these creatures were put aside in specific buckets, all the sediment that was left was sieved and many more amphipods, isopods, polychete , bivalves, cumaceans and many other creatures were collected and sorted carefully soon after in the laboratory.
The biodiversity of this area is known to be very high and this catch is another example of the high efficiency of this small and simple sampling gear perfectly adapted to collect macro-benthic organisms in good condition.
After this day and a few hours of sorting and identifying, everything was fixed and will be used by many scientists for numerous ecological studies, PhD theses and a more general understanding and knowledge of the Antarctic ecosystem.
Henri Robert, Royal Belgian Institute for Natural Sciences
Photos: H. Robert