For a long time it was an unsolved mystery how animals can spread out between those rare oases of energy in the deep sea. One hypothesis was that sunken whale carcasses, large dead algae, and also sunken wood could serve as a food source and temporary habitat for deep-sea animals, but only if bacteria were able to produce methane and sulfur compounds from it. To tackle this question, the team deposited wood logs on the Eastern Mediterranean seafloor at depths of 1,700 meters and returned after one year to study the fauna, bacteria, and chemical microgradients.
The team of researchers observed that the wood-boring bivalves had cut large parts of the wood into smaller chips, which were further degraded by other organisms. This activity led to the consumption of oxygen, enabling the production of hydrogen sulfide by sulfate-reducing microorganisms. And indeed, the researchers also found a mussel, which is normally only found at cold seeps or similar environments where it uses sulfur compounds as an energy source. "It is amazing to see how deep-sea bacteria can transform foreign substances such as wood to provide energy for cold-seep mussels on their journey through the deep ocean," says Antje Boetius, chief scientist of the expedition. Furthermore, the researchers discovered unknown species of deep-sea worms, which have been described by taxonomic experts in Germany and the USA. Thus, sunken wood does not only promote the dispersal of rare deep-sea animals, but also form hotspots of biodiversity on the deep seafloor. (© Max Planck Institute for Marine Microbiology)