Changing Seas - Season 6

Crinoids have been around in various forms since before the age of dinosaurs. Now experts descend into the deep to study the animals from a submersible.

Each summer, the world's largest known aggregation of whale sharks occurs just off the coast of Cancun, Mexico, giving experts the opportunity to learn more about the largest fish in the sea.

The unique oceanic conditions of the Galápagos Islands serve as a perfect natural laboratory to study how climate change may impact corals in the future.

Strange and prehistoric-looking, Smalltooth Sawfish were once coveted by anglers as popular trophy fish. But habitat loss and overfishing have greatly reduced the animals' range and landed them on the endangered species list in 2003.