How Long Do Jellyfish Live? Are They All Immortal?

Understanding the lifespan of jellyfish is crucial for marine ecosystem management and conservation, as jellyfish play significant roles in oceanic food webs and nutrient cycling.

Polyp Stage: The Early Life of a Jellyfish

The life cycle of a jellyfish is a tale of transformation. Jellyfish begin life in the polyp stage, as larvae attached to a solid surface on the ocean floor.

During this stage, polyps are tiny, cylindrical structures that can reproduce asexually. They're little factories that either create even more polyps or move on to the next life stage themselves.

This stage is crucial as it sets the foundation for the jellyfish's life. Polyps can remain in this stage for years, waiting for the right environmental conditions to continue their development.

For example, in the Mediterranean Sea, where a few species of jellyfish thrive, polyps can form dense colonies on submerged rocks and other surfaces. These tiny jellyfish polyps are resilient and capable of withstanding all sorts of environmental stresses (think changes in temperature and salinity).

Polyps also play a significant role in the reproduction process, as they produce medusae through a process called "budding."

Medusa Stage: The Adult Life of a Jellyfish

Jellyfish start to look like jellyfish after transitioning into the adult medusa stage. This is when they become the free-floating creatures we're familiar with, complete with an umbrella-shaped bell "head" and trailing tentacles.

This is also is when jellyfish move away from asexual to sexual reproduction, releasing eggs and sperm into the water to create polyps that become the next generation.

Adult jellyfish — from the cannonball jellyfish to the box jellyfish and beyond — are known for their ability to swim and capture prey, including small fish and crustaceans. Jellyfish stings from their tentacles immobilize their prey, allowing them to feed efficiently.

The medusa stage varies in duration among species. For example, the moon jellyfish has a relatively short lifespan, living for about a year. Other species, such as the lion's mane jellyfish, one of the largest on Earth, can live for several years.

Jellyfish Species and Their Lifespan

The lifespan of jellyfish varies significantly among different species, ranging anywhere from a couple months to (theoretically) 66 million years.

Environmental factors, including water temperature, availability of food and pollution levels, significantly impact jellyfish lifespans. Predation by sea turtles and other marine animals also plays a critical role in determining how long jellyfish live.

Jellyfish mortality rates and lifespans vary widely. Some species live only a few hours, others a few months or a few years — and then, you have the immortal jellyfish, but we'll get to them a little later. Essentially, the answer depends on which jellyfish species you're taking about.

1. Predation

Predation is a significant factor in jellyfish mortality. Sea turtles, for instance, are well-known predators of jellyfish. Other natural predators include fish, birds and even other jellyfish species. For example, comb jellies, which are closely related to jellyfish, are known to feed on smaller jellyfish and their larvae.

Polyps are also vulnerable to predation by animals like sea slugs and crustaceans. These predators can significantly reduce the number of polyps that survive to transition into the medusa stage, thus affecting overall jellyfish populations.

2. Environmental Factors

Environmental factors such as temperature changes and pollution also affect jellyfish lifespans. In fact, changes in temperature can have profound effects on jellyfish populations. For instance, in tropical regions, jellyfish tend to grow and reproduce more rapidly due to the warmer water.

However, sudden changes in temperature or prolonged exposure to pollutants can lead to increased mortality rates among jellyfish populations.

Pollution, particularly plastic waste and chemical contaminants, poses significant threats to jellyfish, affecting their health and reproductive capabilities.

3. Disease and Other Health-related Issues

Jellyfish are susceptible to disease and other health-related issues, which can impact their lifespan. Bacterial and fungal infections can weaken jellyfish and make them more vulnerable to predation and environmental stressors.

Jellyfish belong to the same phylum as rough coral and squiggly sea anemones: cnidaria. They're like distant cousins in the ocean world.

While jellies are the free-floating members of this family, coral stays put and forms vast underwater structures called reefs, which provide homes for many sea creatures. Then there are sea anemones, which may look like funky underwater flowers but are actually predatory animals, anchoring themselves to rocks or coral and using their tentacles to catch food.

Despite their differences, all three cnidarians share a common feature: stinging cells that help them capture prey and defend themselves.

Jellyfish death can occur due to various factors, including injury, disease and natural senescence (aka old age).

Injuries from predators or environmental hazards can also lead to jellyfish death. Disease and other health-related issues can significantly impact jellyfish populations, particularly in polluted or stressed environments.

Additionally, jellyfish stings can sometimes cause injuries to themselves or other jellyfish, leading to an untimely end.

The Role of Senescence in Jellyfish Mortality

Senescence can impact jellyfish lifespan, with some species experiencing a decline in health and function with age. For most jellyfish, senescence eventually leads to death as their biological functions deteriorate.

However, the immortal jellyfish's ability to revert to an earlier life stage allows it to avoid the typical aging process, providing valuable insights into cellular mechanisms that could have implications for human health and aging.

While the immortal jellyfish (Turritopsis dohrnii) can theoretically live forever, it is not immune to predation, disease or other environmental factors that can ultimately lead to its death.

But, under the right conditions, the creature can continuously rejuvenate itself — when faced with environmental stress, physical damage or simply aging, this jellyfish can revert to its polyp stage, essentially starting its life cycle over again.

Implications Beyond Jellyfish Life Stages

The immortal jellyfish's astounding ability has significant implications for scientific research, particularly in the fields of aging and regenerative medicine. By studying how these jellyfish seemingly cheat death, researchers hope to unlock secrets that could lead to breakthroughs in understanding human aging and developing treatments for age-related diseases.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.