Yoji Okato pulled on his dive gear. The underwater photographer gathered his waterproof cameras. Then he dove into the sea off southern Japan.
When he reached the seafloor, he saw something odd. It was a giant circle in the sand that was two meters (six feet) wide. The sand in the center looked smooth. A pattern of symmetrical ridges piled up around the edge of the circle.
Okato took pictures of the sand sculpture. When he shared his photos, other divers said they’d seen these mysterious circles, too. Yet, no one had ever seen what
made them.
Searching
for a Cause
Soon, people came up with theories about these sea circles. Some said they formed when a UFO landed on the seafloor. The spaceship left a mark in the sand,
they said.
Others thought ocean currents sculpted the sand. The moving water could push the sand into ridges. But, the circles seem too perfectly round to be formed by shifting water currents.
To solve the mystery, Okato teamed up with scientists and filmmakers. Time after time, they returned to the dive site where he first saw a sand circle.
The team watched and waited to see how the circles formed. Dive after dive, they saw nothing and swam away without
any clues.
Yoji Okato
sand circle
Asia
Japan
A pufferfish moves sand as it flaps its fins and swims along the seafloor.
Seeing Is Believing
Finally, the team caught the artist in the act. It wasn’t an alien, and it wasn’t an ocean current. It was a male pufferfish small enough to fit in a person’s
cupped hands.
The fish swam back and forth. His motion made tiny waves in the water. These waves moved the sand, forming a circle. Then the fish used his fins to dig into the sand. He flipped fine sand into the center of the circle. He dug dips and built ridges around the edge. Finally, he collected bits of shells in his mouth and carefully placed them on the ridges.
The pufferfish worked on his project for more than a week. Bit by bit, he built a sand sculpture hundreds of times bigger
than him.
Mystery Solved
Okato’s team didn’t just find out what builds the mysterious sea circles. They learned why the pufferfish builds it.
When a female pufferfish swam by, the male zipped back and forth inside the circle. He stirred up the fine sand. He tried to get the female fish’s attention. It worked. She decided to lay her eggs in the center of the circle.
It took patience and a lot of observation. Yet, years after his discovery, Okato finally solved the mystery of the sea circles.
A pufferfish swims back and forth as it makes a sand circle.