Very pretty, but I doubt that it's real. bubbles don't form into skinny little rings and travel horizontally for entended periods of time like a smoke ring.IMHO At the very least the ring would break into individual bubble and head for the surface. Bubbles moving ahead of the "emitting" dolphin would be much like a flag pointing into a very brisk wind, since water has several hundred times the density of air.
On the other hand, I agree about the caging of these intelligent creatures for our amusement. If the dolphins had an exit, could come and go, and THEN came back to perform, that would be a reason to celebrate all those fun tricks