Jellyfish are amazing creatures with an astonishing array of body types, rich colors, and painful stings. The most familiar looking jellyfish are the dome-shaped, radially symmetrical medusae, though there are completely different body types across jellyfish in general. The most recognizable jellyfish come from the taxa Hydrozoa (colonial species), Scyphozoa ("true jellyfish"), and Cubozoa (box jellyfish with severe stings). They range in size from less than a millimeter to over 2 meters in diameter !
From ancient times to modern, they have been a source of food, medicine, and fascination for humans. Their simplicity has helped them to exist for hundreds of millions of years as members of one of the earliest branching lineages in the animal kingdom, the Cnidarians, which also include corals and sea anemones.
There are thought to be thousands of species of jellyfish, though there is debate on what exactly a jellyfish is . Jellyfish are hard to classify and even harder to define. Some jellyfish aficionados prefer the term "gelatinous plankton", but not all gelatinous creatures are jellyfish. Jellyfish are also capable of actively swimming against ocean currents, unlike many other planktonic species. Across all jellyfish, there are widely varying features, abilities, and life histories, though they all live in the water column, are planktonic, buoyantly gelatinous and most are transparent .
Jellyfish can be found in oceans around the world from the shallow intertidal zones to the deep sea pelagic zones. They can also be found in freshwater habitats like lakes. They are opportunistic colonizers with great larval dispersal , meaning their young are carried around the world on water currents and they find most habitats usable. Many people are familiar with jellyfish from reading news of blooms or from personal experience at the seashore feeling a sting. Despite this negative type of interaction, jellyfish have a number of benefits to humanity through ecosystem services. They act as carbon sequesters, have symbiotic relationships with commercially important fish, are food for humans, and provide tourism opportunities .
Jellyfish are complex far beyond the scope of this website to go into detail, so further reading is highly recommended! Books and journal articles used to create this website can be found here.
You can also find information about jellyfish research on the Links page.
1. Gershwin, L. (2013). Stung: On Jellyfish Blooms and the Future of the Ocean. The University of Chicago Press.
2. Condon, R. H., Graham, W. M., Duarte, C. M., Pitt, K. A., Lucas, C. H., Haddock, S. H. D., Sutherland, K. R., Robinson, K. L., Dawson, M. N., Decker, M. B., Mills, C. E., Purcell, J. E., Malej, A., Mianzan, H., Uye, S., Gelcich, S., & Madin, L. P. (2012). Questioning the Rise of Gelatinous Zooplankton in the World’s Oceans. BioScience, 62(2), 160–169.
3. Gershwin, L. (2016). Jellyfish: A Natural History. The University of Chicago Press.
4. Hardinge, G. (2019). The macroecology of globally-distributed deep-sea jellyfish [University of Southhampton].
5. Graham, W. M., Gelcich, S., Robinson, K. L., Duarte, C. M., Brotz, L., Purcell, J. E., Madin, L. P., Mianzan, H., Sutherland, K. R., Uye, S., Pitt, K. A., Lucas, C. H., Bøgeberg, M., Brodeur, R. D., & Condon, R. H. (2014). Linking human well-being and jellyfish: Ecosystem services, impacts, and societal responses. Frontiers in Ecology and the Environment, 12(9), 515–523.