Strange Circles Off The Coast Of Louisiana, Texas

I was looking at Google Maps today (planning my next vacation, of course!), and I noticed these strange circles off the coast of Louisiana and Texas.

I didn't notice any off of the coast of our other Gulf neighbors.  When I switched to the satellite view, there were no structures visible where those circles are.

What are those circles??  On the map, they appear symmetrical, like they are man-made. Do you have an explanation?  I am stumped!

Click this Google Maps link and see for yourself!

(Google Maps)