Lionfish—like those seen above off Honduras in 2010—can take over seafloor and reef habitat and establish densities of more than 200 adults per acre.
A mature female lionfish produces some two million eggs every year, and those eggs and larvae are carried far and wide by currents—fuelling an ongoing invasion.
"I call them the Norwegian rats of the sea," said George Burgess, director of shark research at the Florida Museum of Natural History. "Just like rats, they are spreading all over the world, and you can shoot them, poison them, or curse them all you want, but they aren't going to go away."
(Related: "Rat Invasions Causing Seabird Decline Worldwide.")
The predatory lionfish is especially bad news for Caribbean coral reef ecosystems, because lionfish threaten to displace native species such as snapper and grouper—especially where those species have already been reduced by overfishing.
Lionfish may also be eliminating helpful species lower on the food chain, such as parrot fish, which are grazers that prevent algae and seaweed from overtaking coral reefs.