Photo of one urchin sleeping in the street, published under permission from Al Kashiv blog

And the reason was because of overfishing, and the fact that a last common grazer, a sea urchin, died.

But when the fish came back and began predating and controlling the urchin population, low and behold, kelp forests emerged in shallow water.

So here we see, for example, a sponge spicule, two bits of coral here, that's a sea urchin spine. Really some amazing stuff.

If you take a sea urchin larva from 8.1, put it in a pH of 7.7 not a huge change it becomes deformed and dies.