Diving Nikoi Islands – We have this at one of our dive sites at Nikoi islands too!
Information extracted from – https://blog.nationalgeographic.org/2013/08/15/whats-this-mysterious-circle-on-the-seafloor
What creates mysterious circles on the seafloor? No, it’s not aliens of the deep—it’s actually pufferfish hoping to snag a mate, a new study says.
Divers first noticed the 6.5-foot-wide (2-meter-wide) circular structures near Japan‘s Amami-Oshima Island about 20 years ago. But no one knew how these so-called mystery circles were constructed—or what was creating them—until now.
The circles, scientists say, are actually nests created by male pufferfish, which spend about ten days carefully constructing and decorating the structures to woo females. What’s more, this industrious pufferfish is thought to be a new species in the Torquigener genus, according to the study, published July 1 in the journal Scientific Reports.
The male fish, which measures less than 5 inches (13 centimeters) long, first uses his body to create peaks and valleys in the sandy bottom around a central circle of smooth sand. He accomplishes this feat by swimming in toward the center of the circle in a straight line and then back around the center in a circular motion.
Before the female fish arrive to inspect his handiwork, the male forms irregular patterns in the fine sand particles of the central circle. He also decorates the peaks of the outer portion with shell and coral fragments.
When a potential female partner arrives on the scene, the male stirs up the fine sand in the nest’s inner circle. If she deems the nest, and the male who built it, satisfactory, she lays her eggs in the center of the nest and leaves.
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