Chief scientist leg 3
Antje Boetius
a.boetius.d at merian.briese-research.de
Weblog 7

Diving into diversity

Thank you, to all of you who kept their fingers crossed. This worked at least for the 12th November (Dive 248), when the ROV came up with an intact cable, raising the hope to have found an immediate solution preventing twists and turns in the cable. However, dive 249 and 250 both required more cable cutting, despite different procedures to avoid the cable twists, including changing the position of the floats, taping the cable and keeping a fixed heading and distance to the wire during the dive.

Thankfully, the ROV team has worked very hard to help us complete the scientific program of the first leg. By taking turns in cable cutting and ROV pre- and after dive checks, and by allowing two dives during the night they managed to get us 2 additional dives in 3 days. Of course dive 250 was a special one: This number means that QUEST4000 has now completed 250 dives, and probably more than 2000 hours at the deep sea floor.
Left: Cable cutting - in the heart of the wiring is the fine glass fiber cable which transport images and data from the ROV to the ship. Here, ROV pilot Werner Schmidt’s hands are busy lapping the glass fiber. (Source: Christian Borowski)
Middle and right:
The 250th dive of ROV QUEST4000 (MARUM). The ROV is coming up. Scientists waiting for their samples. The ROV team is waiting for their ROV. (Source: Gabi Schüssler)
We used these dives mainly to complete our biodiversity sampling scheme, for all benthic size classes from micrometer- to centimeter-sized organisms. For the EU project HERMIONE we will compare the biodiversity of three chemosynthetic ecosystems of the Eastern Mediterranean, separated by 60 to 200 miles from each other. In each ecosystem we have chosen three distinct reduced habitats, of which two are only a few tenths of meters away from each other, and a third one is several hundred meters away. All of these sites are sampled in replication, allowing us to test the spatial scaling of the biodiversity and structure of the communities of microorganisms, meio- and macrofauna. Associated with this sampling scheme, we measure the in situ biogeochemistry of each spot, to be able to test whether the environmental context, for example the energy availability, explains more of the similarity between communities than the geographic distance.

Speaking about biodiversity and scales, Heiko Sahling and Christian Borowski made a really interesting observation. The fractured nature of the reduced habitats seems to increase diversity tremendously. For example, a small black spot of less than 20 cm wide in the middle of a vast area of pelagic sediments was populated so densely by a diverse community that a net sample caught some 8 species of worms and 3 different crustacean species, all aggregating in this tiny but, highly sulfidic spot. None of these organisms can be found outside of the spot in the vast oxic seafloor surrounding this mini-niche – but some of them occur in the larger bacterial mat areas some 50 m away from the tiny spot. How these highly adapted but opportunistic organisms find and populate their habitats and how they share such a small niche remains unknown – similar as the wood boring organisms, they appear to have numerous larvae floating in the water, able to settle in reduced settings via specific cues.
Christian Borowski sieving macrofauna samples (Source: Gabi Schüssler). A net haul of one small sulfidic spot…. (Source: MARUM)…proving to be a biodiversity hotspot: each vessel holds several species of worms and crustaceans extracted by sieving (Source: Christian Borowski)
Between dives we continued mapping the seafloor and the fluid escape structures by a combination of Multibeam, Parasound and camera transects. It is amazing to see what a large fraction of the seafloor is covered by carbonate cements, and again, what a diversity of organisms hide in the crusts. Furthermore, the carbonate crusts appear to keep a record of extinct communities. We have visited some sites, which are littered with bivalve and sea urchin shells which may have accumulated over thousands of years. Other crusts are partially composed of cemented bivalve shells. These bivalves also represent chemosynthetic species, indicating that this whole area has probably been active for geological time scales.
Shells from the seafloor and cemented in crusts (Source: Heiko Sahling). Remnants of echinoderms (Source: MARUM; University Bremen)
Considering this, it seems upsetting that something else also accumulates on the seafloor: the trash of civilization. During our dives, we have estimated that we find one piece of trash every 100m in the deep Eastern Mediterranean. This includes plastic bottles, bags, cans and other litter, which ends up in the sea. Plastic is not degraded by microorganisms, hence it remains forever at the seafloor – what an unpleasant sight.
We hope for more pleasant sights when preparing for our last dive for this leg tomorrow morning … Dive 251, which will be dedicated to carbonate crust and flare mapping.

Antje Boetius
Litter at the seafloor – typical items to be encountered during a 300m transect across the seafloor at 1700 m water depth: a can, a milk bottle, a plastic bag (Source MARUM)
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