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Mosaic Jellyfish
Photograph by Melissa Fiene, My Shot
A mosaic jellyfish floats serenely in the waters of the Coral Sea, about 100 nautical miles from Cairns, Australia. Jellyfish are ubiquitous in the Earth’s oceans. They can thrive in warm water and cold, along coastlines or out in the deep. Their bodies are about 95 percent water. And though they have no brains, jellyfish have somehow been smart enough to survive for over 500 million years.
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Moon Jellyfish
Photograph by David Doubilet, National Geographic
These translucent jellyfish are named for their resemblance to Earth’s satellite—but the species has had an otherworldly experience. In 1991 moon jellies flew aboard the space shuttle Columbia during a study on weightlessness and the development of juvenile jellyfish. Here on Earth, the jellies are commonly found in warm ocean waters worldwide.
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Purple-Striped Jellyfish
Photograph by David Doubilet, National Geographic
A large, purple-striped jellyfish floats in the waters of California’s Monterey Bay, where they sometimes arrive en masse. This jelly can grow up to three feet (one meter) in diameter and appear rather formidable. But its stinging tentacles are used to bring in mostly smaller prey, including zooplankton, larval fish, and fish eggs.
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Jellyfish in Lagoon
Photograph by David Doubilet, National Geographic
With a distinctive pulsing motion, a jellyfish makes its way through the waters of a Pacific lagoon. Most jellyfish tend to simply drift along with prevailing currents. But some use more active methods of self-propulsion, including shooting a stream of water from their mouths. A jellyfish also uses its large, central mouth to consume food and expel waste.
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Pacific Coast Jellyfish
Photograph by Paola Carolina Smania, My Shot
Jellyfish use their dangling tentacles, equipped with hollow, harpoonlike darts loaded with neurotoxins, to sting fish, shrimp, or crabs. The strike leaves its victim stunned for easier consumption. Humans can also receive a painful sting from these toxic tentacles, even those belonging to beached or dead jellyfish. In the case of a few species, like Australia’s notorious box jellyfish, stings can be fatal.
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Lion’s Mane Jellyfish
Photograph by Paul Nicklen, National Geographic
A curious yet cautious diver approaches a lion’s mane jellyfish off the British Columbia coast. The tentacles that make up this jelly’s “mane” can deliver a painful and even potentially fatal sting. But such toxins don’t deter several fish species from feeding on the ample bulk of the cold water-loving jellyfish.
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Comb Jelly
Photograph by Jason Edwards, National Geographic
Ctenophores are commonly called comb jellies because they use rows of hairlike cilia to propel themselves through the water. This unique physiology also causes comb jellies to refract light, so they often shine with a rainbow of iridescent color. In the absence of sunlight, comb jellies can still be colorful, if less vivid. Most species are bioluminescent.
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Mastigias Jellyfish
Photograph by Tim Laman, National Geographic
Does this humble jellyfish help determine Earth’s climate? Studies of these Mastigias jellies in a landlocked Palau lake recently prompted scientists to suggest that the motion of sea animals plays a major role in seawater mixing. Winds and tides are major ocean mixers but sea creatures—including jellyfish—may account for as much as a third of the total, the study suggests. That would mean jellies are significant drivers of ocean circulation patterns and thus help to determine Earth’s climate.
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Crab Carrying Jellyfish
Photograph by Tim Laman, National Geographic
Cassiopea andromeda, the upside-down jellyfish, is named for one of Greek mythology’s treacherous queens. Cassiopeia was punished by Poseidon, who deemed that her constellation often appear upside-down in the sky. Her namesake jelly often lies on the seafloor with its mouth and arms facing the surface, which allows symbiotic algae to collect sunlight for photosynthesis and pass nutrients along to the jelly. Crabs sometimes carry these jellyfish on their backs to serve as a very effective protective shield.
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Crab on Purple Jellyfish
Photograph by David Doubilet, National Geographic
Some animals, like these young crabs and some juvenile fish, can live unharmed among a jellyfish’s venomous tentacles. There, protected from prey, they feed on jellyfish leftovers like zooplankton or larval fish and remove parasites from their accommodating hosts.
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Jelly-Riding Crab
Photograph by Hannah Johnson, My Shot
A crab clings to its floating host as both are swept out to sea near Wrightsville Beach, North Carolina. One role jellyfish play in the marine ecosystem is the transport of other animals across the ocean.
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Jellyfish Lake, Palau
Photograph by Tim Laman, National Geographic
Marine scientists warn that Earth’s oceans may look increasingly like this image—teeming with ever growing populations of jellyfish. Overfishing has eliminated many of the jellies’ natural predators and competitors, while climate change is warming water temperatures to levels preferred by the invertebrates. The combination, scientists say, could produce future seas simply saturated with jellyfish.
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