Collection of corals?

Boarding a speedboat I beat a hasty retreat from that god forsaken island and have arrived on Koh Lanta. My, what a difference!
Decided to stay a bit away from the main beach front so this stretch perhaps doesn’t have the perfect sand but it is covered in what I presume to be washed up coral left over from the 2004 tsunami. Not being a coral expert can anyone clarify this?
Suddenly fascinated, I began watching YouTube videos of the tsunami hitting this part of the coast. By no means the worst hit area but it’s amazing to think that it all the debris remains scattered still. Was trying hard not to focus on it as I was having dinner at one of the tiny beach shack restaurants, which happily seems to be as far as development has got here, but once an image is in your head....
Looking forward to some good beach combing and crab spotting, at least I think that was what was entrancing a couple on the beach earlier.