Open ocean, a vast biotope covering two thirds of the planet, some shallow, some as deep as the mountain ranges are high. The ocean has an immense, precariously complex food chain, varying from microscopic animals, like krill, to whales, which ironically feed mainly on the former. Most species swim or float in it, many coming up for air, while other dive in from land or air, often to feed, but also to procreate on the coast, where some species come to lay their eggs. Even the shore is covered with life, largely based on organic matter, such as corpses.