Worm Community Contributes to Methane Release in Ocean
In the waters off the North Island of New Zealand lives a community of polychaetes from the family Ampharetidae. Polychaetes are essentially marine worms that burrow into sediment and have been creating tens of thousands of tunnels in the ocean floor. As a result, these tunnels provide new conduits for methane trapped below the surface to escape.
This super-charged methane seep has created its own unique food web, resulting in much more methane escaping from the ocean floor into the water column.
While it is not clear which came first, the cycle of the worm success and the release of methane is as such: Bacteria consumes much of the methane, converting it to carbon dioxide, and the worms feast on the enriched bacteria — bolstering their healthy population and leading to more tunnels and subsequently, greater methane release.
Most of that methane is likely consumed by biological activity in the water, scientists say. Thus it will not make it into the atmosphere, where it could exacerbate global warming. However, the discovery does highlight scientists' limited understanding of the global methane cycle — and specifically the biological interactions that create the stability of the ocean system.
"We didn't discover any major 'burps' of methane escaping into the atmosphere," said Andrew R. Thurber, a post-doctoral researcher at Oregon State University and lead author on the study. "However, some of the methane seeps are releasing hundreds of times the amounts of methane we typically see in other locations, so the structure and interactions of this unique habitat certainly got our attention.
Researchers also say that oxygen-rich waters near the seafloor enables the worms to breathe better and in turn consume the bacteria at a faster rate.
"In essence, the worms are eating so much microbial biomass that they are shifting the dynamics of the sediment microbial community to an oxygen- and methane-fueled habitat — and the worms' movements and grazing are likely causing the microbial populations to eat methane faster," said Thurber, who works in OSU's College of Earth, Ocean, and Atmospheric Sciences. "That process, however, also leads to more worms that build more conduits in the sediments, and this can result in the release of additional methane."
"The large amounts of methane consumed by bacteria have kept it from reaching the surface," Thurber said. "Those bacteria essentially are putting the pin back in the methane grenade. But we don't know if the worms ultimately may overgraze the bacteria and overtax the system. It's something we haven't really seen before."
Results of the study are published online in the journal Limnology and Oceanography.
Read more at Oregon State University.
Marine tubes image via Shutterstock.