Divers Spot Mysterious Underwater Circles on the Seabed — Then They Realized What It Really Was

Romantic gestures are universal as it stretches beyond the human race and into the animal kingdom. Several species, ranging from birds to mammals and even fishes, display courtship behaviors, including swans forming heart shapes with their necks to penguins gifting their partners rocks, per World Animal Protection Canada. It is as adorable as it gets. But it was the last thing that confused scientists thought of the mysterious crop circles popping up on seabeds off Amami Oshima Island in Japan. In 1995, divers discovered unique circular structures, intricately detailed, carved into the sand. They sought the expertise of scientists to investigate what they dubbed the “mystery circles”, per a study published in the journal Nature. 

In 2011, the experts finally found the gifted sculptors of the mystery circles somewhat– pufferfish. Pufferfish species are predominantly toxic often posing lethal threats if eaten or touched, per PetMD. But their heartwarming efforts to impress a female fish go way beyond their toxic nature. According to the study, the fish species are usually about the size of 12 centimeters (4.7 inches) but can create a structure 16 times its size to grasp the attention of a female in the hope that she would lay eggs on his creation. 

Scientifically Torquigener albomaculosus, pufferfish put in immense hard work using their pectoral, anal, and caudal fins and remain dedicated for about seven to nine days to complete the structure. The experts installed two observation sites on the seabeds of Seisui and Katetsu beaches and deduced the previously undiscovered phenomenon as the reproductive practices of male pufferfish. The creation process starts with a circular formation in the sand as the pufferfish spins around in circles adding detailed lines inwards to the center, as captured in a video by BBC. What specifically caught the scientists’ attention were the radially aligned peaks and valleys which remain characteristic to this fish species only.

The finer details were created through fin-flapping at regular intervals and their swimming patterns somehow pushed the finer sand particles towards the heart of the circular structure. Interestingly, the males also proceeded to decorate the structure with shells and corals. The study highlighted the three unusual characteristics specific to the pufferfish species. “First, radially aligned peaks and valleys were created outside the nest site, second, the peaks were decorated with shell fragments, and third, fine sand particles were gathered in the nest site to create an irregular pattern,” the researchers explained. They rightly marked it as one of nature's greatest creations. 

It is worth noting that the male pufferfish also faced time constraints to complete all these features before the arrival of a female fish to proceed with the mating ritual. As the anticipated visitor neared the site, the male pufferfish stirred up the sand at the center which became the deciding moment. If the female entered and was impressed by it, mating would take place followed by laying of eggs at the center composed of fine sand particles. The fine sand is crucial and thus, cannot be used more than once. The males then abandon the nest to build another because a single reproductive event consumed a majority of the fine sand. Quite impressively, the male pufferfish are actively involved in the reproduction of their species right from the creation of the crop circles until caring for eggs.