I saw this and was going to post on it. The starfish actually sort of expels its stomach around the coral to injest the polyps. That is really neat.
They said one of the theories on why the starfish is growing to great numbers is that the phosphate and nitrate run-off into the ocean from farm lands is causing algae to increase on the reef. This algae is allowing the starfish fry(forget correct term) to grow to full size instead of a majority starving. They said that a single pair of this starfish could produce something around 250,000 fry in a single spawning.
Another cool thing shown during this show were SPS
and other coral spawning.