Oceans are instrumental in handling the amount of carbon dioxide produced by human activity every year, absorbing close to 25 percent of all emissions. In turn, many sea-dwelling organisms take part in the absorption and conversion cycle of CO2, including jellyfish. A new study posits that jellyfish are much more prominent players in the cycle than previously believed.
Various news sources have been circulating a study conducted by the GEOMAR Helmholtz Centre for Ocean Research Kiel which examines global exportation of carbon gases through gelatinous plankton. Taking part in the study was Mario Lebrato, a Biological Oceanographer with GEOMAR. He, along with researchers from Germany, Spain, the United Kingdom, and the United States, performed both field and laboratory experiments on the remains of gelatinous plankton.
Using samples of scyphozoans, ctenophores, and thaliaceans—or true jellyfish, comb jellies, and salps—the team observed how the various jellyfish sank inside cylinders filled with saltwater. According to Lebrato, the results were unexpected. “The sinking speed of jelly remains is much, much higher than what we expected, about 500 to 1600 meters per day,” he said.
Why is this important? Faster sinking organisms have less time to decay en route to the ocean floor, storing the CO2 released through gradual decay away from the atmosphere for potential millennia. In other words, the high carbon dioxide content absorbed by jellyfish after eating CO2-rich plankton is safely stored away deep within the ocean, where it can be left alone or eaten by benthic organisms.
“We are continuously asked how much organic carbon and CO2 do gelatinous plankton sink worldwide, whether their export capacities are similar to phytoplankton and marine snow, and if an increase of jellyfish in the future will enhance organic carbon export and CO2 sequestration,” explained Lebrato. Now they have a rough estimate with which to answer: scyphozoans had an average carbon content of 26.97 percent, thaliaceans had 17.20 percent, and ctenophores had 1.40 percent.
These numbers are less on average than those of phytoplankton and marine snow, the main particles associated with sinking and storage of carbon gases within the ocean interior, but the sheer population numbers and faster sink rate of jellies gives them the edge in storing CO2 to a greater degree.
“[W]e are just starting to comprehend the fundamental properties that will allow us to better understand the role of jellyfish and pelagic tunicates in the global carbon cycle,” said Lebrato.
Aspects of the study were supported by organizations that included the European Project on Ocean Acidification (EPOCA), the Kiel Cluster of Excellence called The Future Ocean, the German-based BIOACID (Biological Impacts of Ocean Acidification), and the US National Science Foundation Office for Polar Programs. Details of the study were published in the recent edition of the international magazine Limnology and Oceanography.