evidence: Europa’s turtle circus is rarely seen by human eyes. The island is a nature reserve, and its waters are protected. Like its neighbor, Bassas da India, 70-odd miles to the northwest, it is part of the Scattered Islands, five specks of land that ring Madagascar like moons. Remnants of the once mighty French colonial empire, they fly the Tricolor as part of the French Southern and Antarctic Lands. [...] Although Europa and Bassas da India lie close together in the middle of the Mozambique Channel, they are very different places. Europa is a scrub-covered island that is home not only to nesting turtles but also to a million breeding pairs of seabirds. Bassas is an atoll that barely shows above the waterline and has a shark-filled lagoon the size of Manhattan. Both are among the last vestiges of healthy marine ecosystems in the western Indian Ocean—sanctuaries for wild nature in depleted seas. "On the surface these places look like nothing—like insignificant dots," says marine biologist Thomas Peschak, who photographed this article. "But once you’ve dived here, you’re spoiled for the rest of your life." [...] At Bassas da India there are no trees for seabirds to roost in and no beaches where turtles can lay their eggs. Bassas is a young atoll, still forming on its parent volcano, a seamount that erupted from the seabed almost two miles below the surface. From the air it looks like a blue plate with a bite-size chunk missing from its northeast rim.