Colonization of deep-sea wood by various organisms.
Credit: Christina Bienhold et al.
Scattered throughout the world's oceans are "wooden cities of life," providing oases for drifting microbes and small animals, a new study has found.
These sunken chunks of wood, along with other organic material like dead whales, may act as stepping stones for a variety of bizarre creatures that also thrive near hydrothermal vents, where super-heated water spews out of the seafloor, said Christina Bienhold, a researcher at Germany's Max Planck Institute for Marine Microbiology.
In a recent study, Bienhold's team placed logs on the bottom of the eastern Mediterranean Sea and found that a wide variety of life sprung up there in the span of only a year, including newfound species of aquatic worms, she told OurAmazingPlanet.
The results of the study, published earlier this month in the online journal PLoS ONE, were especially surprising given that this area is one of the most food-deprived spots in the world's oceans. It thus wouldn't necessarily be expected to harbor a great diversity of life, Bienhold said.
"Nevertheless, a variety of organisms managed to localize, settle, grow and reproduce on our experimental wood deployments," she said.
One of the newly discovered creatures, found by a collaborating scientist, is a species of bloodworm, which feeds on small invertebrates. Another researcher analyzed a different type of marine worm found near the wood, concluding it represented a new species and genus (the taxonomic classification above species). This creature is related to the fireworm, known for its nasty sting.
The most important animals found on the logs were wood-boring mollusks, which showed up in large numbers and began to drill holes and break down the wood, Bienhold said. Her team found that by digesting the wood, these animals produced nutrients that fed a whole different group of organisms, including microbes that typically live near hydrothermal vents, she said. [Images: Hydrothermal Vents in Action]
Hydrothermal vents and cold seeps, where methane and other gases bleed out of the ocean floor, were discovered about 30 years ago, along with a host of bizarre creatures that live in these extreme environments, Bienhold said. Since then, scientists have puzzled over how these animals evolved and travel between these isolated oases. Scientists had asked, "How can these organisms, which depend on specific energy sources for their symbiotic bacteria, disperse across the vast energy-deprived ocean?" she said.
Craig Smith, a researcher with the University of Hawaii at Manoa, who wasn't involved in this study, has found that dead whale carcasses are used by these so-called "chemoautotrophic" organisms, which survive by breaking down chemicals like sulfide and methane. This study, he said, also suggests that wood falls can harbor some of these same creatures.
While the wood in the study was placed there by scientists, wood naturally finds its way into the ocean as dead trees fall into rivers and are swept out to sea, when storm debris is taken by surging waters and even from shipwrecks.