Preface The expedition ARK XIX/3 with the German icebreaking RV ...

ROV "Victor 6000"
The ROV "Victor 6000" allowed to collect in total up to 24 cores (25 cm²) of which 3 to
6 cores were assigned to Ghent during 5 dives. Also here all three different habitats
from the HMMV were aimed at to sample. In the bacteria area the sampling was
random within a small area (of maximum 4 m²) although completely covered
Beggiatoa patches were selected each time. At the Pogonophora area, and the
northern active site with mixed habitats, a micro-scale gradient was selected from
inside a dense Pogonophora patch to a less covered area, bare mud and finally a
mixed sample of Beggiatoa and Pogonophora. Cores collected by "Victor 6000" were
always fixed as bulk in formaldehyde (4 %).
Results
No analysis were done on board since meiofauna in fine sediment needs extraction
by centrifugation in a density gradient. Some sediment from in between the
Pogonophora was checked for the presence of meiofauna, and these small amounts
already proved the presence of several specimens belonging to different species.
By return to the laboratory, the samples will be processed, meiofauna will be counted
and identified up to higher taxa level while nematodes will be identified up to species
level and biodiversity estimated. The following hypotheses will be tested:
The presence of a topographic structure or chemical gradients in the deep-sea
changes the meiobenthic community structure and results in an increased regional
diversity. Through community analyses by means of multivariate statistics, species
turnover will be established along a gradient from the summit of the volcano, along
the slope, the outer rim, until the background sediments. 2. The presence of a small
scaled biogenic structure in or on the sediment results in a change of the community
structure by which the local diversity increases. All samples collected in the
framework of the first hypothesis are summarized in Table B5.6-1. In total 5 microgradients
were sampled as summarized in Table B5.6-2
During the last dive an additional sampling was done. When reaching the seafloor
large amounts of dead Gadiidae fish were observed. Taking the opportunity of this
natural experiment in order to investigate the response of the fauna to this event,
samples were collected at 50, 20 and 2 cm from the 60 cm long fish.
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