Lionfish (escapees from aquaria) are aggressive (and poisonous) predators and either kill native fish outright or outcompete them when foraging. When they are introduced to a coral reef, the survival of native fish can drop by as much as 80%. In some regions of Florida, divers who remove them are eligible for a $10,000 prize. In areas where groupers are protected, lionfish are not as big of a problem because the native groupers eat them—another reason to protect communities and try to keep them intact.
Erik Olsen/The New York Times/Redux