Microbiomes in mangroves: a hotspot of biodiversity yet to be explored.

Mangroves are fascinating environments and study sites of great importance due to their huge heritage value and the large number of ecosystem services they provide. These interface areas located between land and sea are inhabited by a wide variety of aquatic organisms (crustaceans, fish, molluscs, polychaetes, annelids, sponges, echinoderms, amphibians, etc.) that represent a tiny part of the biodiversity in these ecosystems. Another invisible component of mangrove biodiversity is made up of microorganisms (especially bacteria and viruses), very abundant in the water and sediment of mangroves but also closely linked to local plants and animals. Although essential to the functioning of the ecosystem and the adaptation of multicellular organisms, this part remains poorly known to date. By using an exploratory approach, we wish to carry out an inventory of the microbial diversity (taxonomic and functional) present in mangroves, in its various forms (planktonic, benthic and epibiotic). In this perspective, 3 emblematic sites will be sampled: in French Guiana (Sinnamary Estuary), Senegal (Sine-Saloum Delta) and Vietnam (Halong Bay), with the aim of identifying the main microbial taxa (pathogenic or not), as well as the main biophysicochemical determinants of this micro-diversity, and to identify a potential biogeographic signature of these microbiomes. The thesis project aims in particular to explore the composition and ecological functions of the main bacterial and viral communities present in water and sediments, but also associated with the main aquatic species (animal and plant) inhabiting mangroves.