Sunken Wood on Seafloor Feeds Deep-Sea Life

A new study finds that sunken wood can develop into attractive habitats and feed various deep-sea organisms.

Deep-sea animals thriving at hydrothermal vents and cold seeps require methane and hydrogen sulfide emerging from the ocean floor for their survival. They carry bacteria on their body which converts the energy from these compounds into food. These vents and cold seeps are separated by deep-sea deserts and there is no connection between them. It remained a mystery as to how the deep-sea animals got dispersed between these isolated areas of vegetation.

One hypothesis suggested that the animals depended on sunken whale carcasses and sunken wood as food sources and temporary habitats for their survival. Now, a team of researchers from Max-Planck-Gesellschaft in Germany have found that sunken wood could attract deep-sea organisms, as bacteria could produce hydrogen sulfide during wood degradation.

For the study, the research team deposited wooden logs on the Eastern Mediterranean seafloor at depths of 1,700 meters. After one year, they returned to study the flora and fauna in that region. Using underwater robot technology, the researchers confirmed that several deep-sea organisms such as mussels and wood-boring bivalves were thriving on the wooden logs.

"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 Christina Bienhold, from Max Planck Institute for Marine Microbiology, said in a statement. "But they also need assistance from bacteria, namely to make use of the cellulose from the wood, which is difficult to digest."

The research team noticed that wood-boring bivalves had split the wooden logs into smaller chips, which were then degraded by other organisms. During wood degradation, sulfate-reducing microorganisms consume oxygen and produce hydrogen sulfide, an energy source needed for the survival of animals found in cold seeps.