Off New Zealand's Poor Knights Islands, this Gem Doris nudibranch, no bigger than three inches and named for its sapphire-like blues, can be spotted both underwater and in shallow rockpools.

On Australia's Great Barrier Reef, a clownfish finds safety in its host anemone, immune to the stings that would turn away most predators.

In Florida’s Key Largo, a Green Sea Turtle glides effortlessly through the water.

On Australia's Great Barrier Reef, this bubble coral seems to breathe, swelling by day toward the light to feed its symbiotic algae, then deflating at night to hunt with hidden stinging tentacles.

Off Lanai's southern coast in Hawaii, this cavern formed when part of an ancient lava tube collapsed, its ceiling opening spilling beams of light, silhouetting a fellow diver.

Off the shores of Aqaba, Jordan, a diver surfaces with one hand raised, a practice that protects against unseen hazards above and helps release expanding air from the buoyancy vest.

At Blue Heron Bridge in Florida, stargazers bury themselves until only their eyes show, lying in wait beneath the sand for prey to pass above.