|Red lionfish (Pterois volitans)|
|Devil firefish (Pterois miles), aka the common lionfish|
I first learned about this problem in 2009 and these animals have only grown more numerous in the past few years. They pose serious dangers to reef organisms, as they are quite voracious predators.
Interestingly enough, they are apparently delicious. So, if you are so inclined, some careful fishing could net you quite the interesting meal.
References are the Global Invasive Species Database, Sailors for the Sea, NOAA, and CNN. Images used are from Wikimedia Commons and are under Creative Commons licenses: one, two.