Enormous “Mystery Circles” Built by a Small Pufferfish on the Sandy Seabed—How and Why Does the Pufferfish Build These Elaborate Geometric Circular Structures?

Abstract

A small pufferfish has been discovered building an elaborate geometric circular structure, known as the “mystery circle,” with a diameter of approximately 2 meters on the seabed of Amami-Oshima Island, Japan, capturing global attention. Our previous research has shown that males build the structure to attract females for mating and to provide a nest for spawning and egg care. The shape and size of the structure have been suggested to influence female mate choice. Two-dimensional computer simulations indicate that the radial patterns surrounding the nest emerge through repeated digging behavior following a simple algorithm. The structure exhibits unique hydrodynamic properties and hold potential applications in biomimetic design.