No, this has nothing to do with aliens, but rather something that puffer fish use for mating. That's right, "the more ridges built into the structure, the higher the chance the fish will mate. Additionally, the small rocks and seashells, so carefully dragged around the periphery of the circle, can serve as sources of nourishment for the small fish." Continue reading for the video and more information.
Female fish are reportedly so attracted to the multilayered ridges sculpted in the sand, that they will seek out the male fish upon discovering his so-called nest. After mating, the couple will then deposit the newly fertilized eggs in the sand at the center of the circle.
Besides being beautiful, the underwater crop circle also serves a highly practical purpose: The carefully carved ridges act as buffers against ocean currents, protecting fertilized eggs from being either moved or swept away.
[Sources 1 | 2]