Is the fate of gelatinous zooplankton biomass and similar structures’ carbon export shaped by climate? And how important is this process in the oceans and for CO2 uptake? A unique dataset compiled in the Mediterranean Sea during 11 years shows that jelly-carbon sinks along entire continental margins. Increasing numbers of gelatinous plankton might regionally hep mitigating the CO2 problem by sinking more carbon out of the surface waters, but how this process relates to climate was unknown. In field surveys, Dr. Mario Lebrato from Scripps Institution of Oceanography (San Diego) and colleagues from GEOMAR (Germany), CSIC (Spain) and the EC Joint Research Center (Italy) showed that dead pelagic tunicates (jelly-carbon) sink fast and reach shelves and slopes in the whole western Mediterranean Sea echoing the climate variability. Jellies are especially important because they rapidly consume plankton and particles, and quickly export biomass and carbon to the ocean interior.

When carbon dioxide from the atmosphere dissolves in seawater, marine organisms convert it to organic carbon and other organic components during photosynthesis. Jellyfish and pelagic tunicates feed on smaller plankton and thus consume the organic carbon. When they sink to the seafloor at the end of their life cycles, they take the carbon from surface waters with them, provide it as food to organisms at the bottom or store it in deep water layers after decomposition. As a result, more CO2 can be dissolved in the oceans depending where and how deep they sink and decompose.

Scientists know that jelly-carbon is sinking in the oceans but for logistic reasons, spatial and temporal patterns are elusive, as well as how the process relates to environmental variables or climate. Together with colleagues from Germany, Spain, and Italy, Dr. Mario Lebrato, working at Scripps Institution of Oceanography, San Diego, analyzed field data from a large survey program called MEDITS where marine commercial species were sampled by trawling. Lucky enough that gelatinous species were also recorded, thus making available this unique dataset. Their new article in the international magazine PLOS ONE describes for the first time how jelly-carbon depositions at the seabed couple with climate and environmental variables. This is fundamental work to understand how gelatinous plankton will respond to climate change and how carbon fluxes will vary in the future.

To obtain the field dataset, the program MEDITS-ES facilitated access to the data via Dr. Joan Cartes and Dr. Domingo Lloris at the CSIC center in Barcelona. The analyses were conducted with Dr. Juan-Carlos Molinero, at GEOMAR Kiel, who is an expert on ecological trends and large-scale temporal bioclimate analyses. Frederic Melin from EC Joint Research Center, Italy provided satellite data analyses and Ms. Laia Beni-Casadella at CSIC helped with geographical information work. The team joint multidisciplinary efforts to put together their different expertise to conduct a robust analysis on this unique dataset.

“The sinking speed of jelly-carbon is very high, above 1000 m per day, which means the carbon arrives at shelf and slope depths very quick”, Dr. Lebrato says. “This provides ecological services to the benthic communities but also isolates the respired CO2 from the upper ocean”. “And, what puzzles us more, is that the jelly-carbon trends are coupled with climate change in the Mediterranean Sea, which means these fluxes may be predictable”. The trends with Chlorophyll and Temperature apart from climate, give for the first time a way to estimate the carbon fluxes from these elusive groups. This is the first step towards integrating gelatinous plankton carbon export in large-scale models. Although the modelling community is still reticent to use the jelly-carbon compartment, mounting evidence supports the notion that gelatinous organisms might play a major role in sinking carbon in the oceans. “Our dataset shows jelly-carbon export along an entire continental margin. This is enough evidence to take these organisms seriously as major players in the carbon cycle”, Dr. Lebrato says.

“We do not know how much organic carbon and CO2 gelatinous plankton sink worldwide, whether their export capacities are similar to phytoplankton and marine snow, but if an increase of gelatinous plankton in the future takes place, it will enhance organic carbon export and CO2 sequestration. And this will be linked to climate. Until recently, few people believed that jelly organisms could play any major role in the carbon cycle, thus there are few data to make comparisons. Consequently, so far the data available are scarce and we are just starting to comprehend the fundamental properties that will allow us to better understand the role of gelatinous plankton in the global carbon cycle.”

Source: PLOS ONE