Acanthaster planci

Scientists have been studying why populations of crown-of-thorns sea stars (Acanthaster planci) have mushroomed in recent decades. Coral reefs can suffer when the sea star's numbers explode because the echinoderm has a healthy appetite and few predators. And they are part of the reason why Australia's Great Barrier Reef is in decline.

A zoomed-in image of the crown-of-thorns sea star.

Klaus Jost,