The City Under the Sea

STORY BY James Sullivan

Published: July 31, 2013

In 1995, some strange circular structures were first observed underwater off the coast of Japan – strange structures jutting out of the sand which reached up to two meters in diameter. The missing portals of Atlantis? Signs of alien visitors? While the discovery sounds like something out of a Jules Verne novel, the creators of these strange and rather intricate formations are at an instant more benign and at the same time, make for a much more intriguing answer to the question than aliens or a lost civilization ever could: male Marine Pufferfish, of the species Torquigener Tetraodontidae.

Although these circles have been uncovered over the past 18 years, only recently have the creators been revealed, as has been their purpose: a courtship ritual, winning females who prefer a larger nest when seeking a mate, according to a study conducted by Dr. Yoji Okata and published in his paper this month. It's not entirely unusual for tropical fish to build nests particularly during mating season, but in several ways the nest of this species is markedly different. The male pufferfish, who never reuse the same nest, establish the structure before mating begins, basing it off of a large circular shape that consists of inner rills and valleys to protect eggs from the detection of predators as well as undercurrents.

Okata noticed that where the structure was built consisted of radially aligned peaks and valleys that had been created outside the nest. second, the peaks were decorated with shell fragments; and third, fine sand particles, of a different color than the rest of the ocean floor, were gathered in the nest site to create an irregular pattern. This constitutes the design that gives these beautiful structures an otherworldly appearance. The similarities of each nesting site suggest too that the designs were not created by the random process of laying out particles of sand and shell, or even by digging a shape of reasonable size and then stopping.

Instead, the fish begin with digging valleys in a circular shape with the use of their pectoral fins, anal fins, and caudal fins while swimming in a linear motion. From there, they swam at angles in a radial direction from the outside of the circle to the inside, forming a network of overlapping inner and outer valleys to insulate the newly spawned eggs. It was then observed that to create the patterns of sand particles, the pufferfish then swam, keeping their fins from flapping as they moved inward. Perhaps the idea that these great structures are the result of pufferfish rather than some distant lifeform is the most intriguing facet, short of actually watching them work, instinctively bringing these elaborate blueprints into being. Perhaps it is because in watching these structures happen, we are watching engineering in its primal phase, a facet that we've always imagined as strictly belonging to humanity. Architecture we've always thought of as human art, and the Marine Pufferfish suggests that these were skills we possessed long before our ancestors ever crawled out of the sea.

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