Jellyfish are soft-bodied invertebrates that drift through the ocean’s water column around the world. They are part of the phylum Cnidaria, which also includes corals and anemones. Jellyfish have stinging cells called nematocysts that they use to capture prey and defend themselves. But even with their stinging cells, jellyfish still end up being prey for a variety of marine animals.
Fish
Many types of fish eat jellyfish, especially in their juvenile stages. Small jellyfish are often eaten whole by fish. Some examples of fish that eat jellyfish include:
- Ocean sunfish
- Pufferfish
- Triggerfish
- Tunas
- Amberjacks
- Ocean pandas
- Bat rays
- Leatherback sea turtles
Ocean sunfish in particular seem to thrive on jellyfish diets. Their flat bodies and small mouths are well-adapted to suck whole jellyfish right in. The stinging cells of the jellyfish do not seem to bother the sunfish at all. Sunfish have even been observed blasting water at jellyfish to stun them before eating.
Many juvenile fish eat small jellyfish and jellies make up the bulk of the diet for larval fish. Young fish seem more willing to brave the stings of jellyfish to gain the nutrition they provide. Jellyfish are over 95% water, but they still provide needed calories, salts, and minerals for developing fish.
Sea Turtles
Several species of sea turtles dine on jellyfish when they encounter them. Leatherback sea turtles are especially known to seek out and consume jellies. Their favorite prey is the lion’s mane jellyfish. Leatherbacks have adaptations like thick skin and downward-pointing spines in their throat to avoid stings while eating.
Other sea turtles known to eat jellyfish include:
- Green sea turtles
- Loggerhead sea turtles
- Hawksbill sea turtles
Young sea turtles seem to be more vulnerable to stings from jellies. But adult turtles actively hunt jelly swarms and can consume hundreds of pounds of jellies per day.
Birds
Many species of seabirds also prey on jellyfish that float near the water’s surface. Diving birds that eat jellies include:
- Northern gannets
- Boobies
- Cormorants
- Penguins
- Shearwaters
- Albatrosses
Some birds even pick up jellyfish from the surface while swimming. Gulls, terns, and frigatebirds are seen feeding on jellies. Birds tend to go after smaller jellyfish species and juvenile stages. Their sharp beaks allow them to get past the stinging cells and consume the soft jelly bodies.
Other Marine Animals
In addition to fish, turtles, and birds, jellyfish are eaten by a surprising variety of other marine animals as well:
- Sea slugs
- Sharks
- Whales
- Polar bears
- Crabs
- Squid and octopuses
- Sea anemones
- Some other jellyfish species
Some marine animals like sea anemones and crabs may scavenge jellyfish that have washed up on shore. Others are known to actively hunt jellyfish out in the open ocean. Huge oceanic whale sharks can suck in tiny jellyfish through their filtering apparatus as they cruise through jelly swarms.
Adaptations for Hunting and Eating Jellyfish
The animals that prey on jellyfish have adaptations that allow them to hunt and consume these unusual soft-bodied creatures armed with stinging nematocysts:
- Thick skin – Leatherback sea turtles and sunfish have very thick dermal layers that resist jellyfish stings.
- Protective mucus – Fish, turtles, and some invertebrates produce mucus that prevents nematocysts from firing.
- Delayed firing – Crabs quickly flick jellyfish against rocks to delay nematocyst firing until after the jellies are consumed.
- Small mouths – Sunfish and sea turtles have small mouths that minimize contact with stinging tentacles.
- Nematocyst resistance – Repeated exposure seems to make some predators less sensitive to stings.
In addition, many predators selectively go after smaller or juvenile jellyfish which have less powerful stings than adult jellies. Predators may target injured or dying jellies that have already expended their stinging cells. Removing jellies from the water or vigorous rinsing can also reduce nematocyst firing.
Jellyfish Predators Face Dangers
While various animals have adaptations to eat jellyfish, dining on jellies still poses some dangers:
- Nematocyst stings can still occur and irritate sensitive tissues like eyes or mouths.
- Stinging tentacles stuck in throat or gills can cause choking or impaired breathing.
- Toxins in some jellyfish can cause illness if consumed.
- Sharp crustacean shells inside jellies may cut delicate tissue.
- Nutritionally, jellies are very watery and low in calories.
- Large jellyfish can obstruct digestive tracts.
Young fish, turtles, and birds seem to face the greatest risks when learning to handle and eat jellyfish. Even predators adapted to jellies can face dangers from occasional large stings or allergic reactions. However, for many marine predators, the trade-off is worth it to gain calories from the abundant jellyfish they encounter.
Importance of Jellyfish in Food Webs
Jellyfish provide an important food source for many marine animals. As jellies proliferate in many overfished ecosystems, they help sustain predators through trophic energy transfer up the food web. Some animals like ocean sunfish and leatherback turtles appear highly dependent on jellyfish blooms. Jelly-eaters also distribute jelly biomass through their own excrement and decomposing bodies after death. This recycles nutrients and energy back into the marine ecosystem.
Some researchers argue jellyfish predation is an important check helping prevent jellyfish from overwhelming ecosystems. Predators that control jellyfish growth and reproduction may help maintain balance in challenged marine environments. However, blooms still occur as human activities continue to foster jelly proliferation in many areas. There is concern that vulnerable predators focused on jellies may suffer from population declines if jellyfish become too dominant.
The takeaway is that jellyfish form a key part of open ocean food webs. Many fascinating marine animals rely on jellies as an important dietary component thanks to specialized adaptations. But ecosystems can become unbalanced if jellies proliferate too extensively from human activities like overfishing, pollution, and climate change.
Conclusion
A diverse array of marine fish, birds, turtles, and invertebrates prey on jellyfish throughout the world’s oceans. While jellies have stinging cells for defense, many animals have evolved adaptations to hunt and eat them with minimal harm. Jellyfish provide nutrition to these predators, especially important to species like sunfish and leatherbacks that target jelly swarms. However, potential dangers from stings and toxins still exist. Maintaining balanced ecosystems is crucial so jelly-eaters do not decline if jellyfish become overly dominant from human impacts on the oceans.