It's hard enough to be a nature photographer — slogging through jungles and enduring the burning desert sun to set up just the right shot of a rare creature. But just imagine doing it all on a half-hour air supply. That's what underwater wildlife photographers like Geoffrey Semorile must do to produce these crisp, brightly colored images of the other three-quarters of the world hidden beneath the sea.

"All underwater creatures know three things about underwater photographers - when you are out of film, when you are in focus and when you are out of air," Semorile says. "They then strike that pose you have been waiting your whole tank of air for, right after you have shot your last frame of film or refocused your lens ten times."