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Balloon fish may be carving mysterious "crop circles" near Australia

Japan’s white spotted balloon fish is famous for producing intricate, ringed patterns in the sand. Now, 5,500 miles away in Australia, scientists have discovered what appear to be dozens more of these creations.

While conducting a marine life survey on the shelf of northwest Australia near the submarine gas infrastructure with an autonomous underwater vehicle, marine ecologist Todd Bond spotted a striking pattern on the seabed, more than 100 meters deep. “Immediately, I knew what it was,” says Bond, of the University of Western Australia in Perth. Bond and his colleagues continued the investigation, eventually finding nearly two dozen more.

Until now, these submarine “crop circles” were found only on the coasts of Japan. First discovered in the 1990s, it took two decades to solve the mystery of who created them. In 2011, scientists found the sculptors, the tiny males of what was then a new species of Torquigener balloon fish. The patterns are nests, meticulously plowed throughout the day and decorated with shells to attract females to lay eggs in the center.

A floating autonomous underwater vehicle (HAUV) deployed along the submarine natural gas infrastructure off the coast of Australia in September 2018 captured images of something startling: a wavy ring carved in the sand. Researchers have finally discovered nearly two dozen of these circles, similar to elaborate nests made by white-spotted balloon fish males near Japan, making it the first such find outside of Japan. Although it is not known which species created the Australian rings, an unidentified balloon fish fled the site of one of them.

Although there is no video confirmation that pufferfish are building nests in Australia, the structures are almost identical to those in Japan, they even share a similar number of mountain ranges, Bond and colleagues report in the Journal of Fish Biology. November 2020. And when a fellow deployed an underwater video system in the area, the device fortunately landed almost directly above a circle and captured images of a small balloon fish fleeing the formation.

Australian circles are located in much deeper waters than the Japanese: 130 meters or more compared to about 30 meters in Japan. Well-known Australian pufferfish in the area typically inhabit shallower waters, raising questions about the identity of the responsible species.

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

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“It’s amazing to find the circles … at a depth where there’s not much light,” says Elisabet Forsgren, a behavioral ecologist at the Norwegian Institute for Nature Research in Trondheim. If nests are to be a visual signal to attract females, they can be difficult to see at such a faint point.

Bond says the discovery raises more questions that may eventually help us understand the evolution of balloon fish, a group already flooded with eccentricities. Not only are they among the most toxic vertebrates on Earth, but they have completely lost their ribs and pelvic bones to make room when they “blow” with water (SN: 8/1/19). Among the questions: if Australian circles are made by a different species than Japan, have the artistic skills of the two fish evolved separately?

“It’s kind of humiliating to know there’s so much out there that we don’t know,” Bond says. "It's also a little scary too. This is obviously a reflection of a key part for the reproduction of maybe a new species, but we don't know anything about it. We didn't even know they existed."

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