Jellies

The Lion’s Mane Jelly, Cyanea capillata , is the largest jelly in the world. Credit: Copyright Alexander Semenov

Cannonball Jelly, Stomolophus meleagris. Credit: angienature. CC BY-NC 3.0

The Lion’s Mane Jelly, also known as The Giant Jelly or Hair Jelly in other parts of the world, has only one true scientific name: Cyanea capillata. Cyanea means “blue in color” in Greek, a descriptor for the color of many of its close relatives, and capillata, means “long hair." Like the Lion’s Mane Jelly, many other jellies have descriptive common names.

The Cannonball Jelly, Stomolophus meleagris, for instance, is also known as the Cabbage Head Jelly because of its resemblance to both an exploding cannonball and a head of cabbage. While descriptive and fun, multiple common names for a single species of jelly can be confusing. Scientists use scientific names to avoid this confusion.

Every species of jelly, and every scientifically described species on Earth, has a single genus and species name. Cyanea capillata, for instance, has a genus name of Cyanea and a species name of capillata. The genus functions like a last name and is shared with other closely related relatives, while the species name identifies the individual. There are at least 14 other species of jellies in the Cyanea genus. Most are found in the colder waters of the Pacific and Atlantic Oceans.

Did you know? The term "jellies" is becoming more frequently used than the term "jellyfish" because the latter term implies that a jelly is a fish. Jellies, in fact, are not even closely related to fishes, which are vertebrates.

Comb jellies have transparent, jelly-like bodies with bright, iridescent color bands, which are made up of tiny hairs called combs. Credit: Copyright Alexander Semenov

More closely related to true jellies, but still quite different, are Siphonophores. Though they are Cnidarians like true jellies, they are from the class Hydrozoa, which means “sea serpent animal” in ancient Greek. Similar to jellies, they live in the open ocean and have stinging cells called nematocysts, but they are quite different in that they are colonial. Individuals attach themselves together in strings where they perform a unique function within the whole. Some perform reproductive functions; others are responsible for capturing and digesting prey. Their colonies can grow to more than 100 feet long and take many forms, the most well-known of which is the Portuguese Man-of-War, Physalia physalis, which has stinging tentacles that can extend dozens of yards, and will sting even if detached from the colony. The Portuguese Man-of-War is comprised of four separate polyps. Its name comes from the uppermost polyp, a gas-filled bladder, or pneumatophore, which sits above the water and resembles an old warship at full sail. 

Did you know? There is no environment on Earth that is too hostile for jellies. Scientists have found hot-pink jellies 2,591m/8,500ft below the ocean’s surface near Costa Rica in deep sea-vents, one of the harshest environments on Earth. Jellies can also be found in the Antarctica in waters below -1˚C/30˚F, as well as freshwater lakes.

Portuguese Man-of-War, Physalia physalis. Credit: Biodiversity Heritage Library

Lion’s Mane Jellies, called "Nomuras" in Japan, have been blooming off the coast of Japan since 2002, crowding the nets of fishermen, and even overturning trawlers. Credit: Niu Fisheries Cooperative. CC BY-NC 2.0

In the face of climate change, the fate of life in the world’s oceans is uncertain, but the Lion’s Mane Jelly and other jelly animals will probably fare well. Warm water holds less oxygen than cold water, so as oceans warm, less oxygenated water will not be available to support life. Jellies dissolve oxygen in their watery tissues, which provides them with a built-in oxygen supply. This allows them to survive in the ocean’s most polluted and oxygen-deprived environments, which are considered “dead zones” for other organisms. Without predators and ecological competitors, and with an abundance of plankton to eat, jellies dominate these areas and reproduce rapidly, often produce jelly “blooms” in which massive numbers of jellies appear in an area at one time.

The number of dead zones around the world are increasing, which means that more of these blooms are likely to appear. In the U.S. alone, there are already known dead zones in the Gulf of Mexico, the Chesapeake Bay, the Narragansett Bay, Long Island Sound, and the Pacific Ocean, off of the Oregon coast. Once a jelly population dominates these stressed areas, they will continue to eat fish, larvae, and other living prey, making it harder for those populations to rebound.

Jelly blooms in Mar Menor, Spain. Credit: Stephanie Booth. CC BY-NC-SA 2.0

Jelly blooms do occur naturally, but are currently forming at staggering rates. The consequences are being experienced around the globe. Large blooms can fill beaches, discouraging beach-goers from entering tentacle-filled waters. Box Jellies, which are some of the most poisonous animals in the world, bloom in tropical waters and are often fatal—to humans.

As well as affecting tourism, jelly blooms wreak havoc on fishing operations by overwhelming fishing nets with their weight, poisoning and crushing captured fish, and clogging the engines of fishing boats. They are also notorious for clogging intake pipes in marine facilities like desalination plants and even nuclear power plants. In the Philippines, in 1999, a bloom large enough to fill 50 trucks clogged the intake pipes of a power plant, causing 40 million people to go without electricity.

Did you know? Chironex fleckeri  is a type of box jelly that can kill a person in three minutes—a world record.