Special plates in the throat called the pharyngeal mill grind up all that material, and the fish literally poop out sand as a result — each parrotfish poops out up to 840 pounds a year.
And because the change doesn't just simply happen overnight, it's not uncommon to see a parrotfish swimming around that's half gray (female) and half green (male).
Before the color change is complete, some species of parrotfish use their half-and-half status as camouflage, deftly sneaking into harems that still have a super-male and fertilizing the females' eggs before the alpha fish knows what's up.
"But to try to fix an entire ecosystem, especially one that's in the water?
It's not easy." But that won't stop them from trying.
Add to this the unfortunate fact that many species of parrotfish are also really heavy sleepers, and you can see there's a problem.