From Wikipedia:

Males create large geometric circles in the sand to attract females for copulation. To construct the ornate circular structure, a male works for more than a week straight. He flaps his fins along the seafloor to build ridges which he then decorates with shells and coral and sculpts a unique maze pattern in the center where a female might lay her eggs if, after evaluating his construction skills, she chooses him. He guards the eggs until they hatch and does not reuse the circles.