Jellyfish can be found floating through the oceans across the world, their translucent bodies pulsing as they propel themselves through the water. If you’ve ever been stung by one of these creatures, you know they can pack quite a punch!
If you’re short on time, here’s a quick answer to your question: While not a regular part of their diet, some shark species have been known to eat jellyfish on occasion when other prey is scarce.
In this comprehensive guide, we’ll take an in-depth look at shark and jellyfish interactions. We’ll discuss which shark species eat jellyfish, why they might choose to dine on these venomous invertebrates, and what effects jellyfish stings have on sharks.
What Kinds of Sharks Eat Jellyfish?
Leopard Sharks
Leopard sharks are one of the most common sharks found along the Pacific coast of North America. They are opportunistic feeders and are known to eat a wide variety of prey, including crustaceans, mollusks, bony fishes, and even smaller sharks.
Jellyfish make up a regular part of the leopard shark’s diet.
Leopard sharks often swim through swarms of jellyfish with their mouths wide open, gobbling them up. The oral cavity and throat of leopard sharks contain small dermal denticles or “skin teeth” that allow them to easily trap and swallow jellyfish without getting stung.
Some key facts about leopard sharks eating jellyfish:
- Up to 50% of a leopard shark’s diet can consist of jellyfish.
- They seem to prefer moon jellies, but will eat other species too.
- In Monterey Bay, they feed extensively on a bloom of moon jellies each spring.
- The sharks time their reproduction so pregnant females can feed on the jellyfish swarms.
So while leopard sharks eat all kinds of prey, jellyfish provide an abundant seasonal food source that they have adapted well to take advantage of.
Basking Sharks
As the second largest fish species in the ocean, basking sharks are gentle filter feeders that swim with their huge mouths wide open to catch planktonic prey. They have often been observed with jellyfish in their mouths, tentacles trailing out between their gill rakers while they feed.
Some key points about basking sharks and jellyfish:
- Jellyfish make up only a small percentage of the basking shark’s overall diet.
- They don’t seem to target jellyfish specifically, but ingest them incidentally while filter feeding for tiny zooplankton.
- All parts of the jellyfish are digested except the hard beak structure made of chitin.
- Jellyfish provide organic matter and an additional food source for these passive yet gigantic feeders.
Whale Sharks
Like basking sharks, whale sharks are huge peaceful filter feeders that cruise the open ocean with their mouths open to catch food. They too are known to ingest jellyfish frequently. Some interesting facts:
- Jellyfish can make up over 25% of the organic matter found in whale shark stomachs.
- Whale sharks seem to target dense gatherings of jellyfish, suggesting they seek them out purposefully.
- The slimy jelly coating may facilitate capturing and swallowing plankton.
- Their diet is more diverse in locations without large jellyfish aggregations.
While plankton like krill and fish eggs are their primary prey, jellyfish provide a substantial nutritional contribution, especially in areas where they form seasonal blooms. The whale sharks’ unique filtration system allows them to take advantage of these gelatinous animals.
Why Would a Shark Eat a Jellyfish?
There are a few reasons why sharks might eat jellyfish despite their stinging cells and overall low nutritional value:
Mistaken Identity
Sharks have poor vision and primarily hunt using smell and vibrations. A jellyfish’s pulsing movements in the water may resemble injured fish or other preferred shark prey. So a shark might accidentally bite a jellyfish thinking it is a meal, only to quickly reject the gelatinous creature.
Curiosity
Sharks are innately curious creatures. Young sharks especially may sample bite odd things in their environment to explore. Jellyfish with their strange pulsing forms could tempt an investigative bite from a shark just to see what they are.
Hunger Desperation
When sharks are very hungry, they may resort to less desirable prey. The toxins and stings from a jellyfish may be worth enduring if a shark has not eaten in awhile and needs sustenance. They have tough skin, so jellyfish stings are likely not too bothersome.
Nutritional Components
While jellyfish are over 95% water and low in calories, they do contain some beneficial nutrients. Jellyfish have collagen protein and omega-3 fats that may appeal to a shark even if most of the meal passes through their system unused.
Self-Defense
Some sharks may bite jellyfish as a defensive behavior. Jellyfish tentacles around a shark’s mouth could trigger a bite reflex. And consuming jellyfish destroys their stinging cells so they can no longer pose a nuisance.
So while jellyfish do not make ideal shark prey, there are several possible motivations for why sharks might eat them occasionally. Sharks are opportunistic feeders, and jellyfish are very abundant in ocean ecosystems.
How Do Sharks Withstand Jellyfish Stings?
Sharks have evolved amazing physiological adaptations that allow them to hunt and feed on jellyfish without being bothered by their stings. Here’s an overview of how sharks can withstand jellyfish stings:
Thick Skin
Sharks have very thick skin, up to 10 times thicker than human skin, that serves as an excellent barrier against jellyfish stings. The outer layer of a shark’s skin contains denticles, which are tooth-like scales made of the same enamel as human teeth.
This armor-like covering shields a shark’s skin from jellyfish nematocysts, the stinging cells that deliver venom.
Immune System Adaptations
In addition to physical barriers, sharks have immune systems that are highly resistant to jellyfish venom. Research has found anti-inflammatory and anti-hemolytic properties in sharks’ blood and tissues that neutralize toxins from stings.
Some sharks even produce immunity-boosting compounds in mucus on their skin when encountering jellyfish.
Behavioral Adaptations
Sharks display specialized feeding behaviors when eating jellyfish that minimize their risk of getting stung. Using their electrosensory system, sharks can detect jellyfish and approach them from angles that avoid contact with tentacles.
Sharks may also turn jellyfish over before consuming them to access non-stinging body tissues first.
Species Differences
Some shark species are more resistant to stings than others. For example, thresher sharks regularly prey on venomous box jellyfish without ill effects. Meanwhile, juvenile lemon sharks show more prominent stress responses after encountering jellyfish compared to adults.
Overall tolerance depends on factors like a species’ exposure history and immune defenses.
Consequences of Eating Jellyfish
Eating jellyfish can have several consequences for sharks. Here is an in-depth look at some of the potential effects:
Nutritional Benefits
Jellyfish can provide some nutritional value for sharks. They are made up of mostly water, but also contain proteins and amino acids that sharks can utilize. However, they do not contain high amounts of calories or fat, so sharks would need to eat a lot of jellyfish to meet their energy needs.
Digestive Challenges
A jellyfish’s body is composed mainly of mesoglea – a non-living, jelly-like substance made up of water, proteins and carbohydrates. This makes jellyfish difficult for sharks to fully digest and break down.
Their digestive systems are adapted for digesting high-protein foods like fish and seals, not gelatinous zooplankton like jellyfish.
Eating large amounts of jellyfish can lead to digestive issues for sharks. The undigested mesoglea can cause obstructions and blockages in their digestive tracts. This can lead to painful conditions like gastric bloating, constipation, or vomiting.
Toxic Effects
Some jellyfish species have stinging cells called nematocysts that contain venom and toxins. If a shark eats one of these jellyfish, it could get stung in its mouth, throat, or stomach lining. This can cause anything from mild irritation to excruciating pain depending on the toxins involved.
Box jellyfish and Portuguese man o’ war jellyfish, for example, inject extremely potent venoms that could potentially kill a shark if enough nematocysts are ingested. Even non-venomous jellyfish species can cause allergic reactions or inflammation in sharks that eat them.
Providing Hydration
While not exactly a nutritional benefit, the high water content in jellyfish can help provide hydration for sharks. This may be advantageous in warmer waters where sharks are at higher risk of dehydration.
Jellyfish are over 95% water, so they can be a rehydrating snack for sharks in between eating energy-dense fish and mammals.
However, the amount of hydration jellyfish provide is likely minimal compared to the amount of water sharks get from their marine environment. Sharks have adaptations like a rectal gland to maintain water balance, so they don’t depend solely on prey for hydration.
Risk of Plastic Ingestion
Unfortunately, another potential consequence is plastic ingestion. Many jellyfish species feed by passively drifting along and capturing plankton and fish eggs. As microplastics permeate the oceans, jellyfish can accidentally consume and bioaccumulate these plastics.
If sharks frequently eat jellyfish containing microplastics, these plastics can build up in the shark’s tissues over time. Plastics can cause internal lacerations, endocrine disruption, and other long-term health effects in sharks and other marine life.
Conclusion
While not a staple food source, some shark species like leopard sharks, basking sharks, and whale sharks have been documented eating jellyfish. They tend to go after the more harmless jelly species, likely to avoid getting stung.
Sharks are opportunistic feeders, so when prey is scarce, they may turn to jellyfish to fill their stomachs. Their tough skin helps protect them from stings. While jellyfish don’t provide much nutritional value, they can help sustain sharks in times of need.
In the end, jellyfish are more hassle than they’re worth for most sharks. But for the jellyfish unlucky enough to end up as an impromptu shark snack, their days are numbered!
