How Did Jellyfish Take Over the Marmara Sea?

Sea of Marmara, Turkey — Locals say the sea is changing, and the evidence is clear: jellyfish now dominate its waters. Once an occasional sight for swimmers and fishers, these gelatinous drifters are appearing in unprecedented numbers. The most common is the Moon Jellyfish (Aurelia aurita), easily spotted from beaches and boats. But they are not alone.

Species Now Found in the Marmara

Recent reports from researchers and citizens have identified a surprising variety:

• Moon Jellyfish (Aurelia aurita)

• Compass Jellyfish (Chrysaora hysoscella)

• Fried Egg Jellyfish (Cotylorhiza tuberculata)

• Mauve Stinger (Pelagia noctiluca)

• Spotted Jellyfish (Phyllorhiza punctata)

• Nomad Jellyfish (Rhopilema nomadica)

• Upside-Down Jellyfish (Cassiopea spp.)

• Liriope Jellyfish (Liriope tetraphylla)

• Sea Walnut (Mnemiopsis leidyi)

• Comb Jellyfish (Beroe ovata)

• Sea Gooseberry (Pleurobrachia pileus)

This expanding list shows just how rapidly the jellyfish community has diversified and multiplied in the Marmara.

Photo: Getty Images

Why Are They Blooming?

Scientists point to a familiar set of culprits: overfishing, climate change, and pollution. With fewer predators, warming waters, and more plankton to feed on, jellyfish populations have flourished. The mucilage crisis—the thick “sea snot” choking Marmara since 2007—has only accelerated the trend, providing jellyfish with a buffet of plankton while driving away the larger species that once kept them in check.

“Overfishing can throw this complex relationship out of kilter,” says Anthony Richardson, ecologist at CSIRO Marine and Atmospheric Research. “By removing a curb on jellyfish population growth, overfishing opens up ecological space for jellyfish. And as jellyfish flourish, their predation on fish eggs takes a heavier and heavier toll on battered fish stocks.”

The result: a cycle of decline where jellyfish thrive as other species disappear.

Jellyfish: Alien Survivors

Though simple in form, jellyfish are remarkably resilient. Their bodies are 95% water, 5% protein, and trace amounts of lipids and salt. They lack brains, bones, and a circulatory system; instead, oxygen diffuses through their skin. They eat plankton, eggs, small fish, and even other jellyfish.

Fun fact: In 1991, NASA sent a thousand jellyfish polyps to space to study how they react in microgravity. Their ability to adapt, even beyond Earth, demonstrates why they are sometimes called “immortal drifters.”

Impact on People

For locals, jellyfish blooms have transformed coastal life. Swimmers report clogged beaches, fishermen pull up nets tangled with gelatinous masses, and stranded jellyfish rot onshore. What was once a pleasure—the simple trip to the beach—has become a challenge.

Photo: Getty Images

The Recovery Process

Restoring balance will not be easy. Experts say efforts must include:

• Reducing mucilage and pollution → to cut the plankton boom jellyfish feed on.

• Protecting fish habitats → so larvae can survive and fish stocks can recover.

• Reducing overfishing → to allow natural predators of jellyfish to return.

• Exploring removal programs → targeted extraction of jellyfish in areas of extreme bloom.

  
  

Ultimately, the story is one of connection. The chain begins with trash entering the sea, grows into bacterial and plankton surges, creates mucilage, and finally enables jellyfish to swarm unchecked. It starts with us—and ends with us.

What Can Be Done?

Curbing jellyfish overpopulation means reducing the pressures we create: trash, untreated wastewater, and overfishing. Every action, from coastal clean-ups to sustainable seafood choices, pushes the Marmara toward recovery.

The jellyfish takeover is a warning—but also a chance. By recognizing the connections between human activity and marine collapse, we can still choose a different future for the sea.