While diving off Amamu Oshima, Yogi Ookata witnessed something that no one else ever had. About 80-feet below the water's surface he spotted bizarre geometric shapes in the sandy bottom. Ookata and some other researchers investigated the "mystery circle." and revealed their findings on a TV show called "The Discovery of a Century: Deep Sea Mystery Circle."
The show revealed that the sand circles were drawn by a small puffer fish. This marine artist even lines his carving with small shells. The researchers found that female puffer fish were more likely to mate with males that made circles with the most grooves. Interestingly, The patterns were also found to neutralize currents and the shells are thought to be nutrients for hatchlings.