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#science4highseas

The expedition, focusing primarily on the faunistic inventory of benthic communities of the Walters Shoal, is carried by the French National Museum of Natural History of Paris (MNHN). The target groups that are preferentially sampled are algae in the summit zone, molluscs, crustaceans, echinoderms, brachiopods, ascidians, and fish. The data gathered by the French Research Institute for Development (IRD) will feed knowledge of the water column, as well as knowledge about pelagic and avian fauna. The expedition has 3 days transit to the Walters Shoal, and around 20 days of operations.

Benthic operations
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Experts will sample benthic fauna between the summit and 1500 m depth. However, the range from the summit to 500 m is preferred because it is in this zone that the phenomena of endemism are most likely. The comparison of the results with those of the region will be carried out, in particular with those of the Malagasy southern continental shelf.

Sampling uses complementary techniques in different bathymetric slices. In diving, the sucker and the brushing baskets allow to sample the small sessile and mobile fauna, in addition to the sight collections. Beyond the depths (50 m allowed), the dredger (so-called "drag Warén") and the trawl with 5 m opening allow to sample all size classes.

Aboard the vessel, residues (baskets, dredging, trawling) are divided and screened, and the samples are broken down into large taxa (phyla, classes). Representative specimens are photographed on the living, and tissue samples are taken and attached for further sequencing.
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Pelagic operations
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Current recorders (ADCP - Acoustic Doppler Current Profiler) and temperature (thermistor chain) are deployed at the beginning of the campaign and then recorded at the end of the campaign, monitoring the evolution of environmental conditions. These continuous measurements will be supplemented by vertical profiles (CTD - Conductivity Temperature Depth) of temperature, salinity, dissolved oxygen, fluorescence and illuminance, carried out at the benthos sampling sites. Water sampling is performed for analysis (onshore) of nutrient salts and chlorophyll. Drifting buoys are also deployed around the site to test hypotheses about the flow induced by the interaction between currents and topography.

For observation of pelagic migratory fauna, an underwater camera is deployed over periods of 12 to 36 hours at different sites for the observation, identification and enumeration of individuals moving within its field of vision. Observers of birds and marine mammals are also on board to make a visual inventory of the species present whenever weather conditions permit.
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Source: Global Marine et Polar Programme (GMPP)  working group

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