Are Jellyfish Decomposers? (What Do They Eat?)

Jellyfish are carnivorous marine animals that feed on planktonic organisms, small crustaceans, fish eggs, larvae, and small fish.

They use their tentacles to sting and paralyze their prey before eating them. Jellyfish are found in all the world’s oceans, from the surface to the deep sea. Some species of jellyfish can grow to be over two meters in diameter!

Jellyfish are not decomposers as they do not eat decaying matter but living organisms like plankton, shrimp and fish. Jellyfish are secondary consumers as they eat other animals that mostly feed on plants in the ocean but larger jellyfish may be considered tertiary consumers as well.

Jellyfish are beautiful creatures with a fascinating life cycle. They start out as tiny polyps attached to rocks or coral reef. The polyps reproduce asexually and release medusa, which are free-swimming jellyfish. After reproducing sexually, the medusa die and the cycle starts over again!

Habitat of the Jellyfish

Jellyfish live in oceans around the world. They mostly live in shallow waters near shore. In some areas, jellyfish are common. In other areas, they cannot be found. Jellyfish are thought to float to shore near shore and move to deeper waters for breeding.

Primary Diet of the Jellyfish

Jellyfish eat zooplankton, small fish, fish eggs, other jellyfish and larvae. They mostly eat single-celled organisms (zooplankton) that float around in the ocean.

Are Jellyfish Carnivores, Herbivores or Omnivores?

Generally, jellyfish are carnivores and eat other animals. However, jellyfish larvae (baby jellyfish) consume more plant material with mostly planktonic organisms (tiny sea creatures like algae) that float or swim in water. As an adult, jellyfish will eat larger animals like crustaceans or larvae of fish.

Feeding Habits of the Jellyfish

Jellyfish use their tentacles to capture zooplankton and small fish and fish eggs. The tentacles then move the prey to the stomach, where it is eaten. Jellyfish may attach to rocks or other objects with their tentacles and use their stinging cells to capture small animals when they come by.

Jellyfish are quite effective and dangerous hunters with they long, almost invisible, tentacles!

Is a Jellyfish a Producer, Consumer or Decomposer?

Jellyfish are consumers because they must eat other organisms for their energy and carbon source. They are secondary consumers because they eat other animals.

Some of the animals jellyfish eat (like crabs) also eat animals themselves and therefore some jellyfish might be considered tertiary consumers! However, no jellyfish species are producers or decomposers.

Why are Jellyfish not Considered Decomposers?

Although jellies do contain bacteria and other decomposer microorganisms in their gut, they are not considered decomposers because they do not eat dead or decaying matter.

Whereas jellyfish are not decomposers, there are many decomposers in the ocean that play a super important role for the different ecosystems! I wrote a blog post about the decomposers in the ocean here.

Are Jellyfish Autotrophs or Heterotrophs?

Jellyfish are heterotrophs because they must eat other organisms for their energy and carbon source. No jellyfish species are autotrophs because they cannot make their own energy.

Where are Jellyfish in the Food Chain?

Jellyfish are just above the bottom of the food chain because they just consume plankton and tiny sea creatures and are prey to many larger organisms themselves.  

Jellyfish are easy targets for other animals, but contain little nutritional value.

What Animals Prey on Jellyfish?

Large fish, sea turtles, sharks, octopuses and other large invertebrates are all predators of jellyfish. Some species of jellyfish are themselves predators of other smaller jellyfish.

Jellyfish have adapted their bodies so that they can move around in the water, but they are quite slow.

Therefore they are an obvious target for other animals, so they have also developed stinging cells on their tentacles in order to defend themselves.

Some animals, like the sea turtle shown here, do not care much about the toxic tentacles of jellyfish.


In this blog post I have looked at the diet of jellyfish and where they belong in the food chain. They are definitely secondary consumers and jellyfish can be considered to have a fairly complex diet considering their simple anatomy!

Jellyfish eat a variety of planktonic organisms during different times of the year. In the winter, there are less algae and planktons in the water, so their food supply is still limited and metabolism lower.

During summer when jellyfish are close to the surface of the water, they mainly consume planktonic organisms. However, larger jellyfish also consume crustaceans and small fish deeper in the oceans. This is what makes these animals so fascinating, and sometimes hard to place them in the food chain.

Times near spring and summer are a time for jellyfish to feed and reproduce, but they may also switch into a dormant stage to protect their own food source. This is why it is hard for us to keep track of jellyfish populations from year to year.