The loss of native fish can do enormous harm to coral reefs (see Reef Invaders). For instance, some native fish graze on tiny plant-like organisms called algae that grow on the corals. Without grazing fish, the algae grow out of control. Algae block the sun from reaching the corals, which can kill them.
Lionfish can live almost anywhere, and they reproduce rapidly. One female can lay 2 million eggs a year! Plus, most predators aren’t interested in eating lionfish. The fish are covered in spines that shoot painful venom. So far, that’s led top predators in the Atlantic, like barracuda, to steer clear.