How do echinoderms contribute to the ecology of the ocean?

Echinoderms have a special role in the ecosystem in which they live as they are responsible for the distribution of more nutrients in the ocean.  Sea cucumbers and sand dollars accomplish this by burrowing deep into the ocean floor allowing deeper oxygenation to occur.  Starfish and brittle stars control the growth of algae on coral reefs, allowing the coral to feed and thrive.  Some sea urchins can burrow into solid rock walls, breaking them apart and releasing nutrients into the water.