Microbial communities associated with the marine degradation of wood – MICADO

Considerable amounts of wood and plant material can be exported punctually by flooding rivers under the Mediterranean climate, contributing significantly to the transport of organic matter across the continental-marine interface. The export of that terrigenous organic material will rise globally in the coming years with the frequency of great floods predicted to increase substantially in a changing climate. While the labile part of organic matter is degraded in coastal waters, larger organic substrates are ultimately exported to greater depths. Submarine canyons, like those described in the NW Mediterranean Sea, are know to facilitate this transfer through a newly described process called "dense shelf water cascading" (DSWC), where dense water sinks and overflows the shelf resulting in a cascade of water flowing into canyons. These cascading events result in carbon export from the continental shelf to the canyons and play a significant role in the ecology of the deep-sea. The discovery of DSWC has renewed interest on canyon research as it challenges the classical view of vertical settling particles, and it is now considered as one of the main drivers for the transfer of organic material to the deep Mediterranean Sea.
Large organic terrigenous debris, such as wood, are channelled through canyons and accumulate at their mouth. Sunken woods deposited on the seafloor create organic rich habitats characterized by high abundance of specialized or opportunistic invertebrate species. These deposits could thus play an important role for the diversity and functioning of canyon ecosystems considered as "biomass hotspots". Until recently, very little was known on sunken wood ecosystems but interest emerged after comparative studies between sunken wood and hydrothermal vent fauna suggested that sunken wood plays a major role in the adaptation, dispersal, and evolution of chemosynthesis-based communities on the sea floor.
Microbial communities directly degrading the wood and representing the base of the sunken wood ecosystem remain poorly studied. But preliminary results indicate that sunken woods harbour a tremendous microbial diversity and a dynamic chemical environment. Nevertheless, the identity of the wood degrading microbial communities, their ecological function and their metabolic pathways are still mostly unknown.
Because canyons, through their role in the transport of organic matter from shallow to great depth, are emerging as key features for the biodiversity and functioning of marine ecosystems, and because the export of terrestrial organic matter to the sea is predicted to increase, it becomes crucial to understand the faith of large organic falls transferred along the terrestrial/coastal/deep-sea continuum. In this context, the aim of the present research project is to unveil the dynamics of the diversity and metabolisms of microbial communities degrading sunken woods, while considering their reciprocal relationships with habitat biochemistry and chemistry.
By tackling this issue that has not been addressed in previous studies, we will contribute to achieve a better understanding of the mechanisms driving the establishment of biodiversity on these substrates, which constitutes the central theme of the GDRE Diwood network.
The project will benefit from the on-going development of a submarine canyon experimental station in the Lacaze-Duthiers canyon nearby the marine research station of Banyuls-sur-Mer. The station is complementing long-term observations held by the Observatoire Océanologique and partners in the area. The Lacaze-Duthiers canyon has early been shown to contain plant remains, and is regularly affected by dense water cascading. This site is particularly relevant for expanding the series of wood immersion experiments realized under the frame of the GDRE DiWood network.