Paddletail snappers

Swimming off the edge of a coral atoll into the big blue is exciting for a diver. But it's less exciting for fish high on the menu of local predators. Guraidhoo Corner off South Malé Atoll, in the Maldives, is outside the reef and attracts many reef sharks. Paddletail snappers in this exposed environment respond to anything bigger than them, including a human diver, by bunching into a tight, defensive ball.
© Alexander Mustard, Snappers in synchrony - Shell Wildlife Photographer of the Year 2006, owned by the Natural History Museum and BBC Wildlife Magazine and sponsored by Shell, the 2007 exhibition open on 27 October.