Coral reefs are some of the most diverse and valuable ecosystems on Earth and support more species per unit area than any other marine environment. Scientists estimate that there may be another 1 to 8 million undiscovered species of organisms living in a
Pacific walruses travel according to the movement of the ice. As the ice expands in the winter, they move south. As it breaks up and retreats in the spring and summer, they move north again. This image is from Great Migrations.