Wood colonization experiments in the Eastern Mediterranean deep sea

Sunken wood and other large food falls provide a concentrated, locally restricted input of organic material to the otherwise largely oligotrophic deep seafloor. Local degradation processes may lead to reducing conditions and high sulfide concentrations, attracting chemosynthetic communities. These habitats have therefore been proposed to act as stepping stones in the evolution and distribution of chemosynthetic communities in the deep sea. It is, however, not well understood when and how sulfidic conditions develop at wood falls and which bacterial communities colonize the wood. The aim of this study was to contribute to a better understanding of wood fall ecosystems and their role as biological and biogeochemical hotspots in the deep sea. Starting in 2006, systematic deployments of large wood colonization experiments were conducted in the Eastern Mediterranean deep sea, in the vicinity of an active cold seep area in the Central Nile Deep Sea Fan (BIONIL cruise, RV Meteor M70/2 with ROV Quest, Marum, Germany). Experiments were revisited and sampled one year later in 2007 (Medeco-2 cruise, RV Pourquois Pas? with ROV Victor 6000, Ifremer, France). To investigate the biogeochemical and microbiological processes leading to the development of sulfidic niches at wood falls, we sampled/analyzed wood as well as surrounding sediments. In situ and ex situ measurements of sulfide and oxygen were conducted to characterize biogeochemical properties around the wood falls. 454 massively parallel tag sequencing was applied to describe bacterial communities colonizing the wood and surrounding sediments after one year at the seafloor. This work is integrated into the ESF EUROCORES EURODEEP project CHEMECO, the CoML project CHESS, and the European Research Group GDRE DIWOOD (CNRS-MPG).