By Rebecca Campbell Gibbel, DVM
The egg-yolk jelly, Phacellophora camtschatica
AN EXPLOSIVE SITUATION
What do jellyfish, rats and city pigeons have in common? They are universally disliked and proliferate wherever humans are dense. There is a reason for their multiplication, and the animals are not responsible! People have profoundly damaged the natural environment, either intentionally or unintentionally. The resulting deterioration of the ocean and land has made conditions hostile to the original diversity of other species. Only the organisms that tolerate the altered state can survive in degraded environments, while more sensitive species die out.
Climate change is driving higher ocean temperatures, which increases jellyfish metabolism and reproduction. They can thrive in polluted, acidified waters that other marine creatures cannot tolerate. As humans take excessive numbers of fish from the ocean, the predator fish that eat jellyfish are removed, and there are also fewer small fish competing for the same food. These anthropogenic interventions have favored jellyfish, whose populations have responded by increasing dramatically. Jellyfish have existed on earth for half a billion years, starting well before dinosaurs, and despite their fragility, they will probably survive the next mass species extinction.
WHAT THEY ARE
Jellyfish are a component of coral reef and oceanic food webs, but unlike their cnidarian coral cousins, jellyfish have been significantly increasing in numbers. They also periodically experience sudden superabundances, which are poetically called “blooms” or, less fondly, “swarms or smacks”. The term “jellyfish” is a general name for several different groups of gelatinous animals, such as the large and colorful scyphozoa, and the hydrozoa, which includes the dreaded Portuguese man o’ wars. Other jellyfish are the small but lethal cubozoan box jellies and the beautiful staurophores, which are anchored on stalks and do not swim. There is a separate category of oddly shaped jellyfish relatives known as ctenophores, or comb jellies, with small comb-like hairs to propel them through the water. All jellyfish have nematocyst stinging structures, though the severity of the sting varies widely.
The tiny Chironex fleckeri Australian box jellyfish can inflict a sting so powerful that it can cause excruciating pain and cardiac arrest and is known for creating a sensation of impending doom in those who are envenomated (Little et al., 2003). Despite its small 1 cm size, it is considered the most venomous animal in the world.
Even though humans did notintend to create a perfect environment for jellyfish domination, that is what we have done, so we should probably recognize more of the advantages and disadvantages of our association with them.
A LOVE-HATE RELATIONSHIP
Animals like spiders, snakes, and jellyfish tend to be justifiably unpopular because they can inflict pain and sometimes death with their venom. However, dangerous animals also inspire fascination, at least behind glass or cage walls. When jellyfish swarm, they find novel ways to be inconvenient, such as when they take down nuclear power plants and submarines by clogging water intake pipes. They can cause mass destruction to fish farms as they drift in, sting, and suffocate the closely confined salmon and caviar sturgeon.
It is hard to overlook these negative items, but to be fair, we should recognize that jellyfish have good qualities, too! Many of the positive characteristics of jellyfish are easy to understand, so we will start with them and then move to their more abstract benefits.
OBVIOUS BENEFITS FOR HUMANS
- Cannonball jellyfish (Stomolophus meleagris) and jelly blubber (Catostylus mosaicus) are commonly consumed in Asian diets. As with extracts from other animals like rhinoceroses, jellyfish have been used in traditional Chinese medicine as aphrodisiacs (Doyle et al., 2014). Now that the global human population is 8.1 billion, perhaps it is time to stop making aphrodisiacs!
- Mucus from jellyfish binds oil particles and may help break down oil spills (Frost, 2023).
Jellyfish produce increased mucus when stressed, which interacts with oil and breaks it down. This photo shows surface mucus from a moon jellyfish, mixed with oil droplets and sloughing from the surface. Experiments at the University of Texas at Austin found that jellyfish could be used to aid in cleanup of ocean oil spills.
- An extremely useful compound isolated from the Aequorea victoria jellyfish is the Green Fluorescent Protein (GFP), known as the “Living Light Microscope.” GFP is a natural dye that allows molecular biologists to see which genes are active in living cells. Mutant color versions of the GFP proteins, seen in the sketch below, are widely used in medical research to allow the identification of specific gene functions.
- Research by Lee et al. (2018) found that venom from Nemopilema nomurai jellyfish exerts an anti-metastatic effect in cancer cell cultures.
- Derivatives from Caryddea marsupialis and Caryddea tuberculate jellyfish reduce the cell viability of different human cancer cell lines cells, indicating that jellyfish may be a potential source of future anti-cancer drugs (Riccio et al., 2022).
MORE ABSTRACT BENEFITS TO THE ENVIRONMENT
- Jellyfish consume small zooplankton and accumulate organic carbon in their bodies. At the end of their lives, they sink to the seafloor and bring the carbon in their bodies to deep water organisms. After they decompose, the carbon is stored in deep water layers, which sequesters carbon out of the atmosphere so it does not contribute to greenhouse gas formation.
- Swimming jellyfish contribute to oceanic mixing due to water displacement as they move through it. While ocean mixing does not sound all that interesting, the humble jellyfish are playing their part in helping the ocean distribute and absorb planetary heat and carbon (Doyle et al., 2014).
- Jellyfish are essential predators in pelagic marine systems- some say the most important ones in the ocean. Their role as carnivores suggests scary velociraptors but applies to jellies, which consume other animals like tiny zooplankton, small fish and crustaceans, and other jellyfish.
- In the oceanic food web, jellies act as predator and prey and are eaten by hundreds of marine species, including tuna and swordfish, penguins, and leatherback turtles.
- Jellyfish can act as a 3D habitat for other organisms, like floating hotels and snack bars. Juvenile fish, amphipods, and crabs benefit from their shelter, and when the hitchhikers get hungry, they can nibble on their gelatinous ride (Hamilton, 2016).
- And finally, as aquaculture techniques evolve, jellyfish are increasingly being featured in public aquaria, where their weird beauty captivates the imagination and admiration of visitors- who appreciate the jellies even more because those stinging tentacles are safely behind glass!
REFERENCES
Doyle, T. K., Hays, G. C., Harrod, C., & Houghton, J. D. (2014). Ecological and societal benefits of jellyfish. Jellyfish blooms, 105-127.
Frost, E. (2023, May 11). How Jellyfish Break Down Oil After a Spill. Smithsonian Ocean. https://ocean.si.edu/ocean-life/invertebrates/how-jellyfish-break-down-oil-after-spill
Hamilton, G. (2016). The secret lives of jellyfish: long regarded as minor players in ocean ecology, jellyfish are actually important parts of the marine food web. Nature, 531(7595),
Lee, H., Pyo, M. J., Bae, S. K., Heo, Y., Choudhary, I., Hwang, D., Yang, H., Kim, J. H., Chae, J., Han, C. H., Kang, C., Yum, S., & Kim, E. (2018). Nemopilema nomurai jellyfish venom exerts an anti-metastatic effect by inhibiting Smad-and NF-κB-mediated epithelial-mesenchymal transition in HepG2 cells. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-018-20724-3
Little, M., Pereira, P., Mulcahy, R., Cullen, P. A., Carrette, T., & Seymour, J. (2003). Severe cardiac failure associated with presumed jellyfish sting. Irukandji syndrome? Anaesthesia and intensive care, 31(6), 642-647.
Riccio G, Martinez KA, Martín J, Reyes F, D’Ambra I, Lauritano C. Jellyfish as an Alternative Source of Bioactive Antiproliferative Compounds. Marine Drugs. 2022; 20(6):350. https://doi.org/10.3390/md20060350
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