What Happens When Sharks Eat Toxic Jellyfish?

Jellyfish, with their translucent bodies and stinging tentacles, are a common sight in the world’s oceans. While they may seem like an unlikely meal, some shark species do, in fact, eat jellyfish. This raises the question: what happens when a shark consumes a toxic jellyfish?

Shark Species that Eat Jellyfish

Several shark species are known to include jellyfish in their diet. These include:

• Leopard sharks, which are common along the Pacific coast of North America, consume jellyfish regularly. They have adapted to trap and swallow jellyfish with the help of small dermal denticles, or “skin teeth,” in their oral cavity and throat, allowing them to avoid being stung. In fact, jellyfish can make up to 50% of a leopard shark’s diet, especially during spring blooms of moon jellies in Monterey Bay.
• Basking sharks are gentle filter feeders that often ingest jellyfish while feeding on plankton. While jellyfish only make up a small percentage of their diet, they are still a source of organic matter.
• Whale sharks, also filter feeders, are known to target dense aggregations of jellyfish, which can make up over 25% of the organic matter in their stomachs. They use their unique filtration system to take advantage of these gelatinous animals.
• Tiger sharks are also known to eat jellyfish, including juvenile jellies.

Why Sharks Eat Jellyfish

Despite jellyfish being low in nutritional value, there are several reasons why sharks might eat them:

• Mistaken Identity: Sharks have poor vision and may mistake a jellyfish’s pulsing movements for injured prey.
• Curiosity: Especially young sharks might sample jellyfish to explore their environment.
• Hunger Desperation: When very hungry, sharks may eat jellyfish, even if they are not ideal prey. Their tough skin makes stings less bothersome.
• Nutritional Components: Though mostly water, jellyfish contain collagen protein and omega-3 fats, which can be beneficial to sharks.
• Self-Defence: Sharks might bite jellyfish to destroy their stinging cells if they get too close.

How Sharks Withstand Jellyfish Stings

Sharks have several adaptations to avoid the negative effects of jellyfish stings:

• Thick Skin: Sharks’ skin is up to ten times thicker than human skin, and has denticles, which act as an armour against jellyfish nematocysts, the stinging cells that deliver venom.
• Immune System: Sharks have immune systems that are resistant to jellyfish venom, containing anti-inflammatory and anti-hemolytic properties that neutralise toxins.
• Behavioural Adaptations: Sharks can use their electrosensory system to avoid jellyfish tentacles and may turn jellyfish over to access non-stinging tissues.
• Species Differences: Some sharks are more resistant to stings, with some, such as thresher sharks, eating venomous box jellyfish without any apparent adverse effects.

Consequences of Eating Jellyfish

While sharks have adaptations to deal with jellyfish, there are still some potential consequences:

• Nutritional Benefits: Jellyfish provide some proteins and amino acids, but they are mostly water and low in calories.
• Digestive Challenges: Jellyfish are difficult to digest, and the undigested mesoglea can cause obstructions and digestive issues.
• Toxic Effects: Some jellyfish have potent venom that can cause mild irritation, pain, and in extreme cases could be fatal to sharks if enough nematocysts are ingested. However, sharks have tough membranes that can protect their eyes from the venom.
• Hydration: The high water content of jellyfish can provide some hydration, but sharks do not depend on prey for this.
• Risk of Plastic Ingestion: Jellyfish can accidentally ingest microplastics, which can accumulate in the shark’s tissues and cause health problems.

In Conclusion

While not a primary food source, some sharks do eat jellyfish, relying on their adaptations to withstand stings and benefit from the limited nutritional value that jellyfish offer. However, jellyfish are generally more trouble than they are worth for most sharks.