The Blue Realm

They're beautiful - and deadly, with venomous spines that resemble a lion's mane. They're lionfish, a tropical reef species normally found in the Indo-Pacific. Now, they're wreaking havoc in the Caribbean and Atlantic – all thought to have descended from a handful of aquarium fish carelessly released into the sea. In these regions, they are potentially a greater threat to coral reefs and commercial fish populations than global warming or pollution.