Globally, vast amounts of methane are stored below the seafloor. If released on a large scale, this potent greenhouse gas could alter the ocean chemistry and even affect the climate. Fortunately, a benthic “methane biofilter” composed of methane-oxidizing microbes and associated animals, also known as methane-seep biota, can help mitigate this. But how quickly this “biofilter” develops has never been comprehensively recorded. For decades, scientists assumed it was a slow process, based on the very slow growth of anaerobic methane-oxidizing archaea (ANME), key methane-munching microbes in these ecosystems. Most seep-associated animals that live in symbiosis with methane- or sulfur-oxidizing microbes (such as Lamellibrachia tubeworms) are also not known to be speedy growers; in contrast, they are among Earth’s longest-lived invertebrates. Previous models thus predicted a “methane escape window” lasting several decades to 100 years following a seabed leak. Now, the seabed observatory in the South China Sea challenges this view.
Capturing the “Time Zero” of Methane Leak
Between 2018 and 2019, the research team coincidentally captured the onset of a seabed methane leak triggered by gas hydrate exploration. This provided a rare, natural laboratory with a precisely defined starting point of methane leakage. Subsequently, the team revisited the site annually, utilizing multidisciplinary technologies including multibeam echosounders, high-speed underwater cameras, chemical sensors, and biological analyses, to track the dynamic physical, chemical, and biological characteristics of the leaking area.
Astonishing Response Rate of Methane-Oxidizing Microbes
The most surprising finding was the rapid response and proliferation of anaerobic methane-oxidizing archaea (ANME). The team found that the doubling time, i.e., the time it takes for a cell to divide, for these microbes during the initial leakage phase was only 20–40 days, significantly shorter than the previous estimates based on natural samples and laboratory incubations (100–200 days). This represents the fastest growth rate ever recorded for ANME in a natural environment.
Animal-Microbe Teamwork Boosts Methane Removal
Fast-growing methane-oxidizing microbes feed burrowing worms (Spionid polychaetes), which proliferate to densities of tens of thousands per square meter within 1–2 years. These worms churn the seafloor like tiny gardeners, supercharging the methane-oxidizing microbes by pumping oxidants (oxygen, nitrate, sulfate) from seawater into sediments. This ingenious animal-microbe teamwork forges an effective “methane biofilter,” consuming most dissolved methane before it can escape into the overlying water column.
Why It Matters
By tracking a methane leak from its precise starting point, this six-year study has, for the first time, reconstructed the early formation of a methane-consuming cold seep ecosystem. As Professor Andreas Teske noted in his commentary, while cold seep biota have long been viewed as “life in the slow lane,” this research “offers hope that the rapid microbial response to newly initiated seepage can keep pace with methane hydrate dissociation in the gradually warming ocean.” As global changes are escalating the risk of seabed methane leakage, these findings are crucial for refining global ocean methane cycle models, predicting future ocean health, and optimizing deep-sea resource development strategies. Broader, long-term seabed observatory networks are urged to constrain the mechanisms governing these accelerated ecosystem responses.
Research Team
The study was conducted by an international joint team with researchers from the Guangzhou Marine Geological Survey (China), Shanghai Jiao Tong University (China), Third Institute of Oceanography, Ministry of Natural Resources (China), University of Georgia (USA), Marine Biological Laboratory (USA), and University of Bremen (Germany). Dr. Qianyong Liang, Dr. Longhui Deng, and Dr. Ruize Xie are the co-first authors; Dr. Longhui Deng, Dr. Xiyang Dong, and Dr. Fengping Wang are the corresponding authors.
