Fast-sinking jellyfish could boost the oceans’ uptake of carbon dioxide

The Helmholtz Center for Ocean Research (Kiel):  How much more carbon dioxide (CO2) will the oceans be able to take up? To find out more about the efficiency of this service, scientists estimate the sinking velocities of organisms involved in the biological pump. Increasing numbers of gelatinous plankton might help in mitigating the CO2 problem. In field and laboratory experiments scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel have shown that dead jellyfish and pelagic tunicates sink much faster than phytoplankton and marine snow remains. Jellies are especially important because they rapidly consume plankton and particles and quickly export biomass and carbon to the ocean interior.

...To assess the efficiency of the biological carbon pump, data on sinking velocities of the different species are necessary. Together with colleagues from Germany, Spain, the United Kingdom and the United States, Dr. Mario Lebrato, Biological Oceanographer in Prof. Andreas Oschlies’ group at GEOMAR Helmholtz Centre for Ocean Research Kiel, conducted field and laboratory experiments with gelatinous plankton remains. Their latest article in the international magazine “Limnology and Oceanography” describes for the first time the sinking speed of organic remains from jellyfish and pelagic tunicates. Together with a previous article in the same journal that calculated biomass export efficiency for these organisms for the first time, these new data allow robust estimates of global carbon export associated with gelatinous plankton.

...“Our dataset provides an initial overview and comparison for modelers and experimentalists to use in subsequent studies examining the role of jellies in carbon export and the efficiency of the biological pump”, Lebrato says. “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. Until recently, few people believed that jelly organisms could play any major role in the carbon cycle, thus they have been excluded from large biogeochemical research programs. In consequence, the data available up to now are scarce and we 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.”

Accumulation of pelagic jellies. New experiments indicates that fast-sinking jellyfish could boost the oceans’ uptake of carbon dioxide. Photo: Veronica Fuentes, found on the GEOMAR website

Boom in jellyfish: overfishing called into question

Science Daily: Will we soon be forced to eat jellyfish? Since the beginning of the 2000s, these gelatinous creatures have invaded many of the world's seas, like the Japan Sea, the Black Sea, the Mediterranean Sea, etc. Is it a cyclic phenomenon, caused by changes in marine currents or even global warming? Until now, the causes remained unknown. A new study conducted by IRD researchers and its partners, published in Bulletin of Marine Science, exposes overfishing as the main factor.

Jellyfish predators, such as tuna and sea turtles, are disappearing due to overfishing. However, jellyfish are primarily taking advantage of the overfishing of small pelagic fish. Just like these cnidarians, sardines, herring, anchovies and more feed off zooplankton. Thus, they represent their main competition for food. In areas where too many of these fish are caught, they free up an ecological niche. Jellyfish now have free rein and can thrive. Furthermore, small fish eat the eggs and larvae of jellyfish. Therefore, under normal conditions, they regulate the population. In their absence, there is nothing to stop the proliferation of these gelatinous creatures.

In order to demonstrate the major role played by overfishing, researchers compared two ecosystems belonging to the same ocean current, the Benguela, which flows along the south of Africa. The first ecosystem is located off the coast of Namibia. Here, fish stock management measures are not very restrictive. The stocks are barely restored before fishing activities start up again. Jellyfish are currently colonising these coastal waters. The second ecosystem is located 1,000 km further south, off the coast of South Africa. Here, the opposite is true: fishing has been tightly controlled for 60 years. The jellyfish population has not increased....

A jellyfish at the Kyoto Aquarium, shot by Oilstreet, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license