The mystery of the beautiful circular designs that sometimes appear on the sandy sea floor near Amami-Oshima island in Kagoshima Prefecture has been solved by a researcher and local divers.
It turns out pufferfish have been creating the designs, called “mystery circles” by local residents.
The team recently reported in the British journal Scientific Reports that marine pufferfish make geometric circles about two yards in diameter for reproduction purposes.
Hiroshi Kawase, 47, chief scientist at Chiba prefectural Natural History Museum and Institute, and local diving guide Kimiaki Ito, 39, installed video cameras at depths from 20 to 30 yards to monitor and film the pufferfish’s nesting process.
According to the report, a male fish about 4 inches long begins digging sand with his pectoral and tail fins, creating an intricate circular structure in seven to nine days. When the nest is complete, a female comes to lay eggs in the center of the circle. Then the male fish stays near the eggs to protect them until they hatch after a few days.
Kawase believes this pufferfish is a new species of the genus Torquigener, which lives mainly in Southeast Asia.
“I’m very impressed by the designs, and I’m surprised to hear that this is a gobally significant finding,” Ito said.