Photoshop :: Create Animated Shadow Cast Down On Ocean Floor By The Waves Above

I'd really like to create an animated shadow cast down on the ocean floor by the waves above. That nice ripply effect where the light peaks through the waves onto the sand below. I need it to animate too, I think that will be very hard.

I can't post links at the moment but a simple Google image search of "stingray ocean floor" should yield some nice examples. I can't actually find any tutorials similar enough to adapt for this purpose. (I'd like to have the light ripples as the transparent part, and the shadows varying shade of grey to black)