THEMISTO: Toward Hydroacoustics and Ecology of Mid-trophic levels in Indian and SouThern Ocean

The ZATA LTSER welcomes a new scientific programme, called “THEMISTO”, led by Cédric Cotte. The biodiversity of the Southern Ocean is still poorly known, whereas it is under growing threats related to climate change and overfishing. The shear size of this ocean as well as its weather conditions present a sizeable challenge to scientists, somehow limiting our ability to acquire enough data on biodiversity, whenever it is most needed.

Cedric Cotte proposes an alternative way of assessing diversity and abundance: by using hydroacoustic detection at different depth ranges, he aims at quantifying not only abundance of zooplankton and micronekton, but also at distinguishing taxonomic groups and species. This technology will allow to model the three dimensional distribution of these species on wide latitudinal gradient, spanning from sub-tropical regions to polar regions.

An acoustic image obtained from a transect between La Réunion island and Kerguelen islands. The color scales indicates the signal amplitude, wherein yellow and red colors are the highest density of organisms. The signal structure completely changes as the latitude crosses the 40° value.

At the same time, physical processes are recorded (temperature, salinity, but also satellite data) in order to correlate the community composition to the physical structure of the ocean. These results are then interfaced with other programmes to improve our understanding of the ecosystems structure and dynamics.

Species of the Kerguelen ecosystems. Myctophid fishes are an abundant part of the micronekton, on which both marine mammals and birds feed actively.

You can have a look at the French version of this programme here.


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