MOBYDICK - Diving into the Southern Ocean

 

The objective of MOBYDICK is to study the links that exist between the biological pump of carbon and the food web structure. To address this issue MOBYDICK proposes a novel approach by considering the entire food web from microbes to top predators and by investigating the hitherto poorly studied relationships between biogeochemical fluxes and biodiversity.

The dataset required to test the hypotheses proposed in MOBYDICK will be acquired during an oceanographic campaign off Kerguelen Island (Southern Ocean). In this well-documented area, 2 contrasted ecosystems ‘Low Biomass Low Export’ and ‘High Biomass Low Export’ coexist.

MOBYDICK has gathered an international consortium to carry out a wide range of techniques for the determination of stocks, fluxes and biodiversity, which are rarely utilized simultaneously. The results will represent a milestone for fundamental knowledge, but they will also provide essential information for the sustainable management of these vulnerable ecosystems.

During MOBYDICK, we have deployed for the first time a bottlenet at sea. This device is a plankton net of 20 µm fitted into a Niskin bottle and allows to filter and concentrate a very large volume of water in the deep ocean to investigate the nature of settling particles.

Surprisingly, the sinking particles collected at the end of the summer season with this device was largely dominated by single diatom cells, as empty frustules, broken valve debris and resting spores.

Fecal pellets were rare and dominated by mini-pellets (30-50 µm) probably generated by Phaeodarians which were abundantly grazing on diatoms. Chemical, microscopical and metabarcode analyses are currently being analysed for each bottlenet sample and will be compared with surface plankton communities.

 

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A great diversity of planktonic organisms

Corethron inerme
Chaetoceros criophilum
Chaetoceros atlanticus
Fragilariopsis kerguelensis
Asteromphalus parvulus