Massive, million-creature jellyfish blooms can ruin tourist beaches, decimate fishing industries, and even clog the intake pipes for nuclear reactors. But it is a fascinating tale of animal adaptation, and it begins with the jellyfish’s truly bizarre life cycle.
THE BIRDS AND THE BEES
Jellyfish sex 101
For many jellyfish the reproduction process goes like this: When two adult jellyfish (a.k.a. “medusas”) mate and produce a fertilized egg, it floats around the ocean until it finds a hard, flat surface—oyster shells, for example—to stick to.
The polyps, as they’re known in this form, sprout a dozen or so tentacles. When the temperature and currents are just right they begin flowering, separating into frilly, pulsating ridges that eventually detach and swim free—a process scientists call “strobilating.”
These ridges turn into baby jellyfish—a smaller version of the full-grown medusas. Those that survive eat like crazy until they grow into the gelatinous blobs, and the cycle begins anew.
BY THE DIGITS
$350 million: Estimated cost to the Black Sea’s fishing and tourism industries from a proliferation of comb jellyfish.
The immortal life of certain jellies
Turritopsis dohrnii, also called the Benjamin Button jellyfish, is smaller than a fingernail when full-grown and has the incredibly unique ability to revert to a polyp when in danger. That means (like its cinematic namesake) it ages in reverse.
“In a process that looks remarkably like immortality, the born-again polyp colony eventually buds and releases medusae that are genetically identical to the injured adult,” according to the American Museum of Natural History.
A LITTLE LIST
Three reasons the seas are jellyfish friendly
- Jellyfish have few predators, and the ones that exist—sea turtles, salmon, mackerel and albatross—are increasingly scarce.
- They love natural gas rigs, which serve as a perfect home for baby polyps.
- Some species actually thrive where it’s polluted. In China, runoff from the Yangtze River has formed huge dead zones in the East China and Yellow Seas. Scientists think dead zones are behind the surge in Nomura jellyfish👇 in Japan.
A toxic situation
The dreaded box jellyfish, found in Australia and southeast Asia, has a sting that one research team calls ”the most explosive envenomation process presently known to humans.” Venom injected from its 10-foot-long tentacles “turns the tissue into soup” and can cause death within four minutes. Between 20 and 40 people die from their stings every year in the Philippines.
Then there’s the sugar-cube sized Irukandji, which has mastered the animal kingdom’s most perfect covert murder. The Australia native is hard to see, and its stinger leaves no trace. Around 10 minutes after contact, victims suffer excruciating lower back pain, incessant vomiting, constricted airways, and the “creeping” skin frequently associated with methamphetamine usage.
Victims sometimes succumb to brain hemorrhages, extreme high blood pressure or, in 30% of cases, experience some form of heart failure. One out of five ends up on life support. “It’s difficult to know how many victims the Irukandji have claimed,” writes biologist Tim Flannery, since “many deaths have doubtless been put down to stroke, heart attack or drowning.”
If you can't beat 'em, eat 'em
Danish researchers have figured out a way to turn jellyfish into a potato-chip-like snack, by soaking them in alcohol until their goo turns crispy and crunchy. “The mouth-feel and the aesthetic appearance in particular have gastronomic potential,” said one scientist.
Is there really a jellyfish invasion?
A slew of leading scientists are skeptical that a “jellyfish takeover” is actually happening at all.
It’s clear that blooms are on the rise—both in magnitude and frequency—in some patches of the world, according to research done over the last couple decades.
However, the reigning counterargument was put forth by many of the all-stars of jellyfish biology in 2013. Jellyfish populations, these scientists argued (pdf), go through 20-year “oscillations.” While there has been a small linear rise in jellyfish blooms since the 1970s, it’s not clear whether this trend marks a true shift in the baseline of their abundance—or just another oscillation.
Still, academic journals seemingly love the idea of a global jellyfish takeover. A recent analysis found that a whopping half of published papers suffered from jellyfish invasion bias—a narrative with horror-movie appeal.