American Oceans

Moon Jelly

The Moon jelly, scientifically known as Aurelia Aurita, is a specific species of jellyfish. Moon jellies are sometimes called common jellyfish, moon jellyfish, or saucer jelly.

translucent half-moon-shaped moon jelly aurelia aurita

They are a beautiful species with fascinating habits that researchers try to study closely. The jellyfish are translucent, half-moon-shaped animals that float through the ocean.

Moon jellies surprise scientists with their unusual mating habits, including sexual and asexual reproduction. They mesmerize people with their beautiful colors and strange movements.

Although they reside in the sea, they aren’t very talented swimmers! Read on to learn more about this funky sea creature.

Characteristics & Appearance

First, let’s talk about the strange appearance of these jellyfish. Jellyfish, in general, look like aliens compared to mammals humans are more familiar with.

moon jelly strange appearance like aliens

Their bodies are devoid of a skeleton, and they lack the eyes, ears, and nose we recognize as normal features on an animal.

Weight & Length

Moon jellies are relatively small compared to some jellyfish. They are only about 3 inches long, and their weight is almost nonexistent.

moon jellies full length view

Technically, they can weigh between .005 pounds and .07 pounds. However, moon jellies can grow very wide, up to 15 inches, but most only grow to 7 or 8 inches in diameter.

Physical Characteristics & Color

While jellyfish are known for their lengthy, flowing tentacles that can sting prey, moon jellies have quite short tentacles.

moon jellies short and fringe-like tentacles characteristics

They can only reach out about 2 inches from their body, making them look much less intimidating than other jellyfish species.

The tentacles are thick and fringe-like rather than super thing strings, and ripple as they glacially move through the water.

A staple characteristic of the moon jellies is the four horseshoe-shaped images on top of their bodies. It almost looks like a four-leaf clover without the stem.

Moon jelly colors can vary. The jellyfish are white at birth, and their moon-shaped body will take on shades of blue, pink, or purple as they mature, supposedly based on their diet.

They are translucent and sometimes appear to be glowing when they reflect sunlight in the water. They have an ethereal appearance that people love to gawk at as they float by.

Lifespan & Reproduction

Moon jellies can live for up to 12 months. On average, they survive for about ten months before passing on, and they have a fascinating life cycle and reproductive habits.

It starts with a fertilized egg called planulae, which swim around for about ten days before finally attaching themselves to a surface.

Once attached to a surface, they become polyps, which are bottom-dwelling organisms. Believe it or not, it only gets weirder from here.

The polyps then asexually reproduce, having daughter polys. The daughters transform into sacs of undeveloped jellyfish known as strobilae.

The strobila is like jellyfish larvae, which mature into a juvenile moon jelly. First, they develop into ephyrae, which detach from the polyp sacs to become their own, independent jellyfish. This entire process takes less than two weeks.

Once the jellyfish is a juvenile medusa, it will be another 4-6 months for it to develop into a sexually mature medusa.

The speed of this maturation depends on environmental factors like diet, the salinity of the water, and temperature.

The reproduction process is simple. Male moon jellies release sperm when they float near female jellyfish. The sperm uses water currents to enter the female jellies’ gastric pouches, which contain eggs.

When this occurs, the gastric pouches detach from the jellies and release into the water to begin their lifecycle!


Moon jellies thrive along warm coastal waters and tropical locations. Moon jellies can live in water that is 42 to 66 degrees Fahrenheit, but they thrive in warmer water.

They can also survive in water with salinity as low as 0.6% but will thrive with higher levels of salinity; close to 40% is ideal.

Moon jellies live between the epipelagic and mesopelagic zone. They can be found roughly 600 and 3,300 feet below the ocean surface.

Where Do Moon Jelly Live?

Moon jellies live close to the shore or inside harbors, where the water is warmer and plankton is plentiful.

Moon jellies live around the world, inhabiting the Atlantic, Pacific, and Indian oceans. The strange creatures are most common around the coast of North America and Europe.

The daily life of moon jellies is pretty boring. They float through the water slowly, riding the water’s current; as they move, they disperse their stinging tentacles as far apart as they can in the hopes of catching prey as they move through the water. The moon jellies move at a pace of less than one inch per second, 0.79 seconds to be exact.

Food & Diet

Moon jellyfish are carnivorous and survive off zooplankton, floating through the water super slowly and waiting for plankton to cross their path.

When the zooplankton touches the tentacles, the stinging filaments are called nematocysts that live within cells that run along their tentacles.

What Does Moon Jelly Eat?

Moon jellies mostly eat zooplankton but will also eat zooplankton, comb jellies, and smaller jellyfish that they come across.

Jellyfish, including moon jellies, have a graceful and passive hunting technique. They float through the water, relying on the current until they happen upon prey.

They stretch out their stinging tentacles, usually spreading out wide rather than up and down. They will either move horizontally through the water or sink with tentacles outspread to come down on prey floating in the water.

The cells that run along their tentacles are called nematocysts. Inside the nematocysts, there are small dart-shaped structures; the structures are full of venom that shoot out whenever something comes in contact with the tentacles.

The venom kills some prey but will stun and paralyze larger prey. This action allows the moon jelly to use its tentacles to bring the prey to its mouth for consumption. Moon jellies eat as often as they can and never stop hunting, as they are perpetual predators.

Threats & Predators

Moon jellies have unique predators because of their proximity to the coasts and shores. Rather than only being hunted by sea creatures, they’re often hunted by land animals too.

Human Threats

Humans do not pose a threat to moon jellies, and actually, optimize environments for them to thrive. Due to overfishing and pollution eliminating their predators and ocean temperatures rising, more and more locations become hospitable for them.

Pollution, like microbeads which harm most sea creatures, does not affect moon jellies. Thanks to humans, moon jellies are thriving.

Climate Change & Global Warming

The moon jellies love global warming. They thrive in warm ocean water and love being close to the shore where plankton lives.

The general moon jelly population has increased as the ocean water warms because they mature and reproduce much faster in warm water and during the warm months. Their growth and reproduction slow in the winter months or cold environments.


Moon jelly predators include birds like seagulls, sea turtles, and larger fish like sunfish, triggerfish, or whale sharks.

Because moon jellies swim so close to shore, they sometimes even become victims of crabs that live on the beach.

Other Threats

In some areas of Southeast Asia, humans will eat jellyfish. But moon jellies are not common in those waters and are hardly affected by this.

A threat they pose to themselves is that they wash up on shore and die. This occurrence happens because they couldn’t swim in the other direction fast enough and reside close to shores.

Conservation Status

The moon jelly conservation status is currently Not Extinct. Their population is increasing due to climate change making more spaces habitable for them. As pollution and overfishing eliminate many of their predators, the population flourishes.

Add comment