Pufferfish may be carving mysterious ‘crop circles’ near Australia

Japan’s white-spotted pufferfish are renowned for producing complex, ringed patterns in the sand. Now, 5,500 kilometers away in Australia, scientists have discovered what appear to be dozens more of these creations.

While conducting a marine life survey out on Australia’s North West Shelf near subsea gas infrastructure with an autonomous underwater vehicle, marine ecologist Todd Bond spotted a striking pattern on the seafloor, more than 100 meters deep.  “Immediately, I knew what it was,” recounts Bond, of the University of Western Australia in Perth. Bond and his colleagues continued the survey, ultimately finding nearly two dozen more.

Until now, these undersea “crop circles” were found only off the coast of Japan. First spotted in the 1990s, it took two decades to solve the mystery of what created them. In 2011, scientists found the sculptors — the diminutive males of what was then a new species of Torquigener pufferfish. The patterns are nests, meticulously plowed over the course of days and decorated with shells to entice females to lay their eggs in the center. 

While there’s no video confirmation that pufferfish are building the nests in Australia, the structures are nearly identical to those in Japan, even sharing a similar number of ridges, Bond and his colleagues report in the November 2020 Journal of Fish Biology. And when a colleague deployed an underwater video system in the area, the contraption luckily landed almost directly atop a circle and captured footage of a small pufferfish fleeing the formation. 

The Australian circles lie in much deeper waters than Japan’s — 130 meters or more deep compared with about 30 meters deep in Japan. Australian pufferfish known in the area typically inhabit more shallow waters, raising questions about the identity of the species responsible.

Bond says the images captured of the likely piscean culprit are too poor to make a definitive identification. The circles could have been made by the same species that builds Japan’s nests, the white-spotted pufferfish (Torquigener albomaculosus), or the culprit could be a different, local species — possibly one totally new to science. 

“It is surprising to find the circles … at a depth where there is not much light,” says Elisabet Forsgren, a behavioral ecologist at the Norwegian Institute for Nature Research in Trondheim. If the nests are meant to be a visual signal to attract females, they may be hard to see in such a dim spot.

Bond says that the discovery raises more questions that may ultimately help us understand the evolution of pufferfishes, a group already awash in eccentricities. Not only are they among the most toxic vertebrates on Earth, but they’ve completely lost their ribs and pelvic bones to make room when they “puff” with water (SN: 8/1/19). Among the questions: If the Australian circles are made by a different species from Japan’s, did the two fishes’ artistic skills evolve separately?

“It’s kind of humbling to know that there’s so much out there that we don’t know,” says Bond. “It’s also a little bit scary as well. This is a reflection of, obviously, a key part to the reproduction of maybe a new species, but we just know nothing about it. We didn’t even know these existed.”