Over the past two decades, jellyfish have begun to overwhelm our oceans. In New Zealand, divers are constantly swatting off millions of stinging jellyfish, each no larger than a grain of pepper. In Sweden, a massive cluster of moon jellyfish managed to shut down one of the world’s largest nuclear reactors by clogging the plant’s essential pipes. Meanwhile, in the Sea of Japan, thousands of 200-kilogram Nomura jellyfish with bells two meters in diameter swarm fishermen, snapping nets and devouring local fish.
Around the world, these animals voraciously consume fish eggs and larvae, routinely undermine marine farming efforts, and outcompete adult fish by consuming the resources they need to survive. If things stay on their current trajectory, we could be headed for a future where the entire ocean is thick with jellyfish.
So, is there anything that can keep these gelatinous creatures under control? Enter, the humble sea turtle. There is a wide range of marine animals that feed on jellyfish, but sea turtles are among their most ancient predators. And while every known species of sea turtle preys on jellyfish at some point in their lives, none consume quite as many as the leatherback.
Leatherbacks are the largest species of sea turtle, and they eat jellyfish almost exclusively, devouring well over 1,000 metric tons of them over their roughly 50-year lifespans. This is particularly remarkable because jellyfish are 95% water and very low in calories, so to maintain a healthy weight, the average 500-kilogram leatherback needs to eat roughly 400 kilograms of jellyfish every day. That’s roughly the same weight as a grand piano.
Most sea turtles have thick scales covered in keratin—the same material that makes up nails and claws. This leathery armor protects their skin while they hunt, and any captured prey that tries to escape is impaled on the keratinized spikes lining the leatherback’s esophagus. For most sea turtles, these adaptations make individual jellyfish easy prey.
However, a jelly population’s true defense mechanism is in how quickly they can reproduce. Almost all jellyfish species have evolved to reproduce both sexually and asexually, allowing them to increase their numbers with or without a partner. In tropical environments, jellyfish reproduce constantly throughout the year. But in more temperate climates, species often reproduce all at once in a massive bloom, where jellies multiply at alarming rates.
And humanity is making these blooms much more frequent. Fertilizer runoff from farms introduces chemicals that simultaneously kill other fish and prompt blooms. High water temperatures caused by climate change speed up jellyfish reproduction and extend the reproductive season. Meanwhile, both marine construction and pollution dramatically increase the surface area for jellyfish polyps to attach, grow, and mature.
All these issues require a wide range of policy-based solutions. But one major way to prevent jellyfish populations from getting out of hand is to protect their natural predators—many of whom are currently under threat. Small-scale fisheries that are essential to communities in Mexico and Peru often use gillnets, which unintentionally capture and kill hundreds of sea turtles each year. In the Eastern Pacific, these practices could drive leatherbacks to extinction in the next 60 years.
Fortunately, some researchers have already developed inexpensive tools to minimize these risks. Attaching green LED lights to gillnets has proven useful for allowing sea turtles, dolphins, and even seabirds to avoid fishing gear. Solutions like this should allow small-scale fishers to support their communities while minimizing their impact on our leathery ocean defenders.
Research the lifecycle of jellyfish and create a colorful poster that illustrates each stage. Include details about how jellyfish reproduce both sexually and asexually. Present your poster to the class and explain how these reproductive methods contribute to jellyfish population booms.
Using a variety of materials (e.g., paper, clay, or digital tools), create a model of a leatherback sea turtle and its jellyfish prey. Simulate a day in the life of a leatherback by calculating how many jellyfish it needs to eat to maintain its weight. Share your findings with the class.
Split into two groups and hold a debate on the impact of human activities on jellyfish populations and sea turtles. One group will argue that human activities are harmful, while the other will argue that they can be managed or mitigated. Use evidence from the article to support your arguments.
Work in small groups to design a campaign aimed at protecting sea turtles from threats like gillnets. Create posters, social media posts, and a short video explaining the importance of sea turtles in controlling jellyfish populations and how people can help protect them.
Use online mapping tools to create an interactive map showing locations around the world where jellyfish blooms have caused significant problems. Include information on the causes of these blooms and their impact on local ecosystems and human activities. Present your map to the class.
jellyfish – a free-swimming marine invertebrate with a gelatinous umbrella-shaped bell and trailing tentacles – I saw a beautiful jellyfish swimming gracefully in the ocean.
oceans – a very large expanse of sea, in particular each of the main areas into which the sea is divided geographically – The Pacific Ocean is the largest ocean in the world.
New Zealand – a country in the southwestern Pacific Ocean consisting of two main islands, the North Island and the South Island – I would love to visit New Zealand and explore its stunning landscapes.
divers – people who swim underwater using a breathing apparatus, especially a scuba tank, and explore the underwater world – The divers discovered a shipwreck filled with treasure.
stinging – causing a sharp, burning, or prickling sensation – I accidentally touched a stinging nettle and it left a painful rash.
pepper – a pungent hot-tasting powder prepared from dried and ground peppercorns – I like to sprinkle some pepper on my scrambled eggs for extra flavor.
Sweden – a country located in Northern Europe, known for its beautiful landscapes, high standard of living, and social welfare programs – Sweden is famous for its stunning fjords and picturesque countryside.
cluster – a group of similar things or individuals positioned or occurring closely together – I found a cluster of ripe berries hanging from the tree.
moon jellyfish – a translucent jellyfish with a saucer-shaped bell and short tentacles, commonly found in coastal waters – The moon jellyfish gently floated through the water, its bell glowing in the sunlight.
nuclear reactors – devices that initiate and control a self-sustained nuclear chain reaction, used to generate electricity or produce atomic energy – The country relies on nuclear reactors to fulfill a significant portion of its energy needs.
