Development of chemosynthetic microbial communities in organic falls deployed in the deep Southwest Atlantic Ocean

The assembly and successional processes of microbial communities inhabiting deep-sea whale and wood falls are highly complex and vastly unknown, as a myriad of factors may affect the development of a chemosynthetic-based ecosystem on these organic islands. The chemoautotrophy supported by organic substrates is the basis of long-lasting ecosystems, considered biodiversity hotspots in the oligotrophic deep sea. Understanding how these microbial communities develop and the factors affecting them could shed light on processes related to the maintenance of biodiversity in this environment. We performed a whale- and wood-fall experiment in the southwest Atlantic on the Brazilian continental margin and investigated biofilm-forming bacterial and archaeal communities colonising these substrates, deployed at 1500 and 3300 m depth. The composition of the prokaryotic communities shared some similarities with previously reported organic falls in the north Pacific and the Mediterranean Sea, mainly regarding sulphur oxidising chemolithotrophic taxa from the phyla Campylobacterota and Proteobacteria. Communities were found to be highly different between the organic substrates, as whale fall associated biofilms presented a higher dominance of sulphur oxidising chemolithotrophs. We also observed a significant difference between the two sites, with the whale associated communities at the 1500 isobath presenting a faster establishment of the chemosynthetic taxa. ### Competing Interest Statement The authors have declared no competing interest.