The Strange World of Jellyfish

More than six decades ago, on a quiet summer evening near Old Orchard Beach, I found myself sitting on the back of a lobster boat, staring into the calm waters below. The sea was almost perfectly still, and through the clear water I could barely see the sandy bottom, where I hoped to spot crabs.

My father had left me on the boat while he flew his seaplane over Casco Bay searching for herring for sardine fishermen. He often left me alone for long periods while he worked, leaving me to entertain myself with my own imagination. I cannot remember why we had traveled so far south that evening, but what happened next remains one of my most unforgettable memories.

Slowly appearing beneath the surface were glowing, translucent shapes that looked like floating white moons. At first, I noticed only one, then another, until I realized the water was filled with an entire group of these strange creatures drifting at different depths.

They moved gracefully, with perfect symmetry and a ghostlike appearance. At about nine years old, I had no way to describe what I was seeing except that it looked like another world. The sight was so unusual and beautiful that I was completely fascinated.

“They’re jellyfish,” one of the fishermen behind me finally explained. “White jellyfish. They won’t hurt you. But be careful around the red ones.”

I returned slightly to reality. I already knew that some jellyfish could sting. Friends had told stories of finding red jelly-like creatures washed up on beaches around Cape Elizabeth and Scarborough, where touching them could cause painful stings. The clear and white jellyfish, however, seemed harmless.

When I later shared this memory with marine scientist Nick Record from Bigelow Laboratory for Ocean Sciences, he explained that the jellyfish I saw were most likely moon jellies (Aurelia aurita). The red jellyfish commonly found on beaches were probably lion’s mane jellyfish (Cyanea capillata), another species frequently seen in the Gulf of Maine.

Moon jellyfish and lion’s mane jellyfish

Moon jellies have a rounded, disk-like shape when viewed from above and usually grow to around a foot in diameter. Around the edge of their bell are delicate tentacles that help them capture food such as tiny marine animals, crustacean larvae, mollusk larvae, and even small fish.

Although many people believe moon jellies do not sting, they actually do possess stinging cells. However, their sting is usually so mild that humans rarely notice it.

Lion’s mane jellyfish are very different. They are among the largest jellyfish species in the ocean and are found across many regions, while moon jellies are more commonly associated with coastal waters.

A lion’s mane jellyfish can have hundreds or even thousands of tentacles hanging beneath its body. These tentacles serve both feeding and defensive purposes. Like other members of the phylum Cnidaria, including moon jellies, they contain specialized stinging cells called nematocysts.

The powerful sting of lion’s mane jellyfish

Inside each nematocyst is a tiny capsule containing a needle-like structure. When activated, the cell rapidly turns outward and fires the needle with tremendous force. The venom contains various compounds, including enzymes, proteins that damage cell membranes, and neurotoxins.

A lion’s mane jellyfish tentacle can stretch to extraordinary lengths, with individual tentacles reaching up to 100 feet long. Each tentacle may contain hundreds of thousands of these microscopic stinging structures.

For humans, a lion’s mane sting can be extremely painful. Symptoms may include weakness, dizziness, nausea, headaches, and muscle cramps. In severe cases, people may experience breathing problems, rapid heartbeat, muscle spasms, and stiffness in the back and joints.

No confirmed human deaths from lion’s mane jellyfish stings have been recorded, although scientists cannot completely rule out serious risks because some symptoms resemble those caused by dangerous box jellyfish.

Dangerous box jellyfish and Irukandji syndrome

One of the most dangerous jellyfish groups is the box jellyfish. The Irukandji jellyfish (Carukia barnesi) is a particularly notable example. Despite having a tiny body measuring only about half an inch, its thin tentacles can extend several feet and contain powerful stinging cells.

The initial sting may go unnoticed, but within minutes victims can develop severe symptoms, including intense back pain, breathing difficulties, and muscle cramps. In extreme cases, Irukandji syndrome can cause heart problems, stroke, or death.

These jellyfish are mainly found in tropical regions and the Southern Hemisphere rather than the colder waters of Maine.

Jellyfish blooms and changing oceans

Several years ago, unusually large numbers of lion’s mane jellyfish were reported along the southern Maine coast. Some individuals reached impressive sizes, measuring six or seven feet across. This led some people to suggest that warmer, more polluted waters in the Gulf of Maine might be creating better conditions for jellyfish growth.

Scientists around the world have observed larger and longer-lasting jellyfish blooms in some areas and have suggested that climate change could be contributing. However, Nick Record explained that whether jellyfish populations are truly increasing worldwide remains uncertain. Current research data is incomplete, making definite conclusions difficult.

A jellyfish bloom refers to a large concentration of jellyfish gathered in one area. Researchers have documented major blooms involving species such as comb jellies and Nanomia cara in different parts of the Gulf of Maine.

In 1976, a massive bloom of Nanomia cara became so dense that fishing nets became clogged off the coast of Massachusetts. Scientists suspected these jellyfish might have been feeding heavily on herring larvae and affecting local fisheries.

Why jellyfish blooms happen

The exact causes of jellyfish blooms are complicated and usually involve several factors working together. Water temperature, food availability, predator numbers, oxygen levels, ocean currents, human fishing activities, and coastal development can all influence whether conditions become favorable for jellyfish populations.

As oceans continue warming, researchers are monitoring jellyfish populations closely. Large blooms can damage fisheries, interfere with industrial cooling systems, and create problems for aquaculture operations. For example, moon jellies have been linked to gill problems in farmed fish.

The incredible diversity of jellyfish

Jellyfish are planktonic animals, meaning they mostly drift with ocean currents rather than actively swimming. They vary greatly in shape, size, and life cycle, and they belong mainly to three groups: Cnidaria, Ctenophora, and Chordata.

Most adult jellyfish range from about half an inch to several feet in size. The famous lion’s mane jellyfish can grow much larger, reaching lengths of six or seven feet.

Some jellyfish-like creatures, such as the Portuguese man-of-war (Physalia physalis) and Nanomia cara, are not single animals but colonies made up of many specialized individuals. Each member performs a specific role, such as catching food, reproduction, digestion, or defense.

Some colonies can become enormous. Nanomia cara colonies have been recorded reaching nearly 12 feet long, while giant heart jelly (Praya dubia) colonies can exceed 150 feet in length.

Unique jellyfish reproduction

Jellyfish reproduction is incredibly varied. Their life cycles often include both bottom-dwelling and free-floating stages.

Depending on the species, reproduction may occur through sexual reproduction, asexual reproduction, cloning, splitting, or even the development of new jellyfish directly from reproductive tissues.

Many jellyfish alternate between male and female stages, while some species are hermaphrodites, meaning one individual contains both male and female reproductive organs.

A typical jellyfish life cycle begins when adults release tiny larvae called planulae. These larvae attach to the ocean floor and develop into polyps. The polyps later produce young jellyfish called ephyrae, which eventually grow into adult medusae with the familiar bell-shaped bodies and tentacles.

However, many variations exist depending on the species and reproductive method.

The “immortal” jellyfish

One of the most extraordinary jellyfish species is Turritopsis dohrnii, sometimes called the immortal jellyfish. Found mainly around Japan and the Mediterranean region, this species has a remarkable ability to reverse its aging process.

When damaged or exposed to stressful conditions, adult jellyfish of this species can break apart, but their cells remain alive. Those cells then reorganize, forming new structures that eventually develop back into a younger version of the organism.

Unlike normal reproduction, this process does not create a new individual. Instead, the original animal essentially rebuilds itself from its own cells.

Scientists compare this process to an adult frog transforming back into a tadpole. Other species in the same genus have shown similar abilities, but Turritopsis dohrnii remains the most famous example.

Freshwater jellyfish

Although nearly all jellyfish live in saltwater, a few species survive in freshwater environments. The only freshwater jellyfish commonly found in North America is Craspedacusta sowerbii, also known as the peach blossom jellyfish.

This tiny jellyfish has a translucent white bell about the size of a quarter. It appears unpredictably in ponds, lakes, and streams around the world, although it originally came from China’s Yangtze River region.

The species was first reported outside China in London in 1880, likely after being transported with aquatic plants. It was later discovered in North America in 1885 and was recorded in Maine’s Androscoggin Lake in 1963.

Sightings remain rare because the jellyfish stage appears only occasionally, while the hidden polyp stage is difficult to detect. Fortunately, its sting is not noticeable to humans.

Although researchers have considered using this species to help control mosquito populations, introducing non-native species can create unexpected ecological problems.

Jellyfish: strange and beautiful ocean creatures

Jellyfish may appear alien because of their unusual shapes and mysterious lifestyles, but they are fascinating members of Earth’s ecosystems. Their complex biology, unique life cycles, and incredible adaptations reveal just how diverse life in the oceans can be.

As marine scientist Nick Record has observed, if visitors from another planet ever arrived on Earth, they might not find creatures stranger than our own gelatinous ocean drifters. Yet these strange animals are not only unusual—they are also beautiful and essential parts of marine environments.