In the "Endangered Ocean: Manatees" video from the "Endangered Ocean" series, viewers learn about the gentle and graceful manatees, also known as sea cows, which are crucial to maintaining healthy marine ecosystems. Related to elephants, these large aquatic mammals primarily feed on seagrass, helping to control the plant's growth. The video highlights the three manatee species: West Indian, West African, and Amazonian, all of which face threats of extinction due mainly to habitat loss and boat collisions. Viewers learn about the significance of seagrass ecosystems and the detrimental effects of human activities, such as construction and water pollution, on manatee populations. Important conservation strategies include boat safety education and the creation of slow-speed zones in Florida. The video emphasizes the importance of raising public awareness to protect these endangered species to maintain a balanced ocean environment.