Jellyfish are ancient marine invertebrates that have drifted through oceans for hundreds of millions of years. Their gelatinous bodies and stinging cells, called nematocysts, often lead to the assumption they lack natural predators. However, various marine animals do consume jellyfish despite these defenses, raising questions about how they manage to do so.
Marine Animals That Eat Jellyfish
A surprising array of marine life includes jellyfish in their diet. Leatherback sea turtles are prominent consumers, with their diet consisting almost entirely of jellyfish, including species like the Lion’s Mane. These large reptiles actively seek out jellyfish blooms, demonstrating a specialized foraging behavior.
The ocean sunfish, or Mola mola, is another significant predator, known for its preference for jellyfish and other gelatinous zooplankton. Despite their large size, they consume vast quantities of jellyfish to meet their energetic needs. Various seabirds, such as fulmars and albatrosses, also prey on jellyfish, often pecking at their inner tissues to avoid tentacles.
Other predators include:
Some fish species like grey triggerfish, tuna, and butterfish.
Other jellyfish species, which can be cannibalistic.
Lion’s Mane jellyfish, known to feed on the smaller Moon jellyfish.
Whale sharks, which primarily filter feed on plankton but also ingest juvenile jellyfish.
How Predators Manage Jellyfish Stings
Animals that consume jellyfish have developed specific adaptations to navigate their stinging cells. Leatherback sea turtles possess thick, leathery skin, especially around their mouths, which offers protection against stings. Their unique digestive system features backward-pointing spines, called papillae, lining their esophagus from mouth to stomach. These papillae help them grip and break down their slippery prey while preventing jellyfish from escaping or causing harm.
Ocean sunfish, while not having the same physical defenses as turtles, are largely unaffected by jellyfish stings due to their physiology. Their feeding strategy involves consuming large volumes, and their sheer size may also play a role in their tolerance. Some nudibranchs, a type of sea slug, can even incorporate the stinging cells from their jellyfish prey into their own tissues for defense. Seabirds often employ behavioral tactics, carefully targeting less venomous parts of the jellyfish to minimize exposure to stings.
Why Many Animals Don’t Eat Jellyfish
Most marine animals generally avoid consuming jellyfish. The primary reason for this widespread avoidance is the presence of nematocysts, the specialized stinging cells that deliver venom. These cells can cause discomfort or harm to animals lacking specific defenses.
Jellyfish also have low nutritional value. They are composed of about 95% water, meaning they offer minimal calories, carbohydrates, or proteins. An animal would need to consume an enormous quantity of jellyfish to obtain sufficient energy and nutrients, which is not an efficient foraging strategy for many species. However, some studies suggest jellyfish can provide valuable fatty acids, which might explain why some predators, despite the low overall caloric content, still seek them out, especially in high quantities.
Jellyfish’s Place in the Ocean Food Web
Jellyfish occupy a complex position within the marine food web, serving as both predators and prey. They primarily feed on zooplankton, fish larvae, and eggs, influencing the populations of these smaller organisms. This predatory role helps regulate marine ecosystems.
Jellyfish also contribute to nutrient cycling in the ocean. As they drift through different water layers, they help transport and redistribute nutrients like nitrogen and phosphorus. When jellyfish die, their decaying bodies and waste products provide food and nutrients for bacteria and other organisms, including deep-sea scavengers. They play a role in the flow of energy and nutrients, impacting the wider marine environment.