Marine research

Wood on the Seafloor

An oasis for deep-sea life

27.2.2013 | A team of Max Planck researchers from Germany now showed how sunken wood can develop into attractive habitats for a variety of microorganisms and invertebrates.
By using underwater robot technology, the researchers confirmed that animals from hot and cold seeps would be attracted to the wood due to the activity of bacteria, which produce hydrogen sulfide during wood degradation. Many of the animals thriving at hydrothermal vents and cold seeps require special forms of energy such as methane and hydrogen sulfide emerging from the ocean floor. They carry bacterial symbionts in their bodies, which convert the energy from these compounds into foodstuff. The vents and seeps are often separated by hundreds of kilometers of deep-sea desert, with no connection between them.
Colonization of wood
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(© Bienhold et al., PLoS ONE 8(1): e53590) doi:10.1371/journal.pone.0053590)


Colonization of wood | in the deep sea in three different stages

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.

Dr. Christina Bienhold
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Dr. Christina Bienhold
"We were surprised how many animals had populated the wood already after one year. The main colonizers were wood-boring bivalves of the genus Xylophaga, also named shipworms after their shallow-water counterparts. The wood-boring Xylophaga essentially constitute the vanguard and prepare the habitat for other followers," researcher Dr. Christina Bienhold explains. "But they also need assistance from bacteria, namely to make use of the cellulose from the wood, which is difficult to digest."

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)
Dr. Manfred Schloesser

More information

Source

  • Bienhold C, Pop Ristova P, Wenzhöfer F, Dittmar T, Boetius A (2013) How Deep-Sea Wood Falls Sustain Chemosynthetic Life. PLoS ONE 8(1): e53590. doi:10.1371/journal.pone.0053590

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