Jellyfish are unique and mysterious creatures unlike most other animals on the planet – their cell tissue is made up of around 95% water and they have no brain, heart, lungs, blood, or bones. This may lead you to wonder how they survive in the first place and what it is they live on, particularly if you plan to keep pet jellyfish.
Jellyfish are opportunistic carnivores and typically survive on a diet of various small plants, crustaceans, small fish, fish eggs, and many other sea creatures in the larval stage. A few larger jellyfish species such as the Lion’s Mane jellyfish will consume worms and even other jellyfish.
Depending on what they eat, these strange marine marvels can even change color from pink to purple to red according to the pigment found in their food! There’s so much to learn about a jellyfish’s otherworldly eating habits, so if you ever wanted to know how they eat and digest, what they eat in captivity, and even how they poop, keep on reading!
What Do Jellyfish Eat?
Jellyfish eat various marine plants and animals such as phytoplankton (microscopic algae), copepods (small crustaceans), the larval stage of many small fish species, fish eggs, other jellyfish, and the planktonic eggs of many floating sea creatures.
The Spotted jellyfish can even grow a crop of algae in its stomach and feed on the nutrients produced when photosynthesis occurs. Jellyfish have such a large appetite for various types of ocean food that this can often impact fisheries and local aquaculture!
How Jellyfish Hunt?
Jellyfish come across their prey by passively catching them as they’re carried by the ocean current or by actively using their tentacles and rapid movements to trap their food.
These are known respectively as “cruise hunting and “ambush hunting” whereby prey will swim inadvertently in the path of a jellyfish’s mouth or will be chased by stronger jellyfish species using their long tentacles to propel them forward and ensnare them in a zig-zag swimming pattern.
What jellyfish lack in speed, sight, or the advantage of fins when hunting their food, they make up for in body mass. Researchers at the University of Oviedo in Spain found that their body size is the key to their hunting success as they put more energy into growing larger and save important hunting energy by letting the ocean currents guide them to their prey.
What Do Immortal Jellyfish Eat?
Once immortal jellyfish reach sexual maturity (after a month and once they measure 5mm across), they typically eat similar small creatures in a regular jellyfish’s diet – plankton, fish eggs, larvae, and tiny mollusks.
Despite the name, immortal jellyfish are not entirely immortal. While their unique life cycle allows them to potentially live forever, they can be eaten or starve to death.
What Baby Jellyfish Eat?
A baby (larval) jellyfish known as ‘ephyra’ eats tiny food particles, small fish eggs, the tiny larvae of other creatures, and can even eat other baby jellyfish
It’s helpful to note that if you are ever sold a ‘baby’ jellyfish that has a recognizable round, bell-shaped body, this is in fact an adult jellyfish, no matter how small it is. Baby jellyfish have not yet developed this characteristic yet and look like this, so don’t be duped by opportunistic or unlicensed jellyfish breeders!
What Do Jellyfish Eat in Captivity?
In captivity, pet jellyfish can be fed a varied diet of finely chopped or minced seafood, hatched baby brine shrimp known as ‘Artemia’, krill, and thawed frozen foods. Live food is especially recommended for jellyfish growth and overall health due to its high protein and immunity-boosting properties.
The baby brine shrimp can be purchased readily hatched and frozen or some online jellyfish suppliers sell baby brine shrimp kits, allowing owners to easily hatch their own fresh shrimp at home to feed to their jellyfish.
Experienced jellyfish owners also recommend feeding them specialized powdered jellyfish food, especially when keeping large aquariums of them. This can be sourced online and from most local aquarium or pet supply stores.
What Jellyfish Eat Other Jellyfish?
Smaller jellyfish are often preyed upon by the Fried Egg jellyfish (named so for its elevated yellow egg yolk-like center and white body); the Box jellyfish (possessing a translucent cube-like body), and the Lion’s Mane jellyfish (named for its long and red hair-like tentacles).
These large predators also eat worms, crustaceans, and other plankton but have the size and propulsion power to devour smaller jellyfish species with ease. Terrifyingly, the Fried Egg jellyfish measures 24 inches across and has 25 tentacles, whilst the Lion’s Mane species is 8 feet wide and possesses up to 1,200 tentacles.
In comparison to the size of these jellyfish giants, the average jellyfish normally measures between 1 millimeter and a maximum of 16 inches wide with only 15 tentacles!
How Do Jellyfish Eat and Digest Food?
Jellyfish first stun and paralyze their prey using their tentacles which are covered in tiny poisonous stingers known as ‘nematocysts’. They then use a separate set of tentacles known as their ‘oral arms’ to guide the paralyzed prey from the stinger tentacles and into their mouths on the underside of their bell bodies.
Jellyfish do not have intestines, liver, or a pancreas to digest their food, so instead, they break down their food in their simplified version of a stomach known as a ‘coelenteron’.
Cells in the lining of this coelenteron cavity produce digestive enzymes and send the absorbed nutrients throughout the jellyfish’s body.
Do Jellyfish Eat and Poop Out of the Same Hole?
Yes, jellyfish possess only one opening which acts as a mouth, stomach, and anus all rolled into one! They take prey into the digestive cavity and when all the nutrients have been used up, any waste material is expelled out of the same hole.
Because this single orifice means that jellyfish can technically neither poop nor throw up, jellyfish biologists like Rebecca Helm at the University of North Carolina have amusingly coined the terms “throop” and “manus” (mouth and anus) to explain this unique and strange phenomenon.
How Often Do Jellyfish Eat?
In the wild jellyfish feed constantly as they’re always grazing on floating organisms that come in their path, even when they’re not actively hunting, so it’s hard to determine just how much they consume.
Because of their naturally big appetites, it’s important that you feed your pet jellyfish every day in captivity. Feed them a mixture of live and frozen foods and powdered food as advised earlier – each food type will normally have a dosage recommendation on the packaging if you’re unsure.
How Long Can Jellyfish Survive Without Food?
Jellyfish can normally survive up to 3 days without food but will start to appear smaller, thinner, and more lethargic when they aren’t receiving enough food or enough nutritious food such as live shrimp.
For this reason, feeding them between every 1-2 days is a good rule of thumb so you can observe whether they are bulking up or shrinking down from their normal, healthy size.
For further guidance, the Moon jellyfish keepers over at the Sunset Marine Labs in California provide a visual representation here of how what your pet jellyfish should look like when they have empty versus full stomachs.
What Animals Eat Jellyfish in the Ocean?
Due to their powerful, venomous tentacles, jellyfish are not preyed upon by too many sea creatures. However, there are some ocean predators which can safely consume jellyfish that include:
Sea Turtles
Sea turtles are the main natural predators of jellyfish, specifically Leatherback turtles which live almost exclusively on the gelatinous creatures. Leatherbacks have downward-pointing spines inside their esophagus which trap the jellyfish and prevent them from escaping before the turtle has begun to swallow them.
Ocean Sunfish
At 5,000 lbs, the Ocean Sunfish is the world’s largest bony fish and loves to prey on Moon and Comb jellyfish. This strange millstone-shaped creature of the deep eats jellyfish using its beak-like teeth plates and safely digests the venomous jellyfish thanks to its slimy stomach lining.
Bearded Goby
The mud-burrowing Bearded Goby worm found off the coast of South Africa has developed a fairly recent taste for jellyfish, helping out a coastal ecosystem once on the brink of collapse in Africa caused by overfishing and a high jellyfish population.
Sharks
With the exception of the Great White Shark and Electro Shark that can only eat Blue jellyfish, all shark species that live in open water (pelagic sharks) are immune to jellyfish venom and will regularly eat small jellyfish species as part of their diet.
