The snout of West Indian manatees is bent further down than other species in this family. This may be related to the food habits of this species. West Indian manatees feed mainly on sea grasses growing on the sea floor and the orientation of the mouth aids in grasping these plants. One of the unique characteristics of manatees is their flexible split upper lip which is used to pass food to the mouth. Manatees are opportunistic feeders, eating the leaves of most plants that can be manipulated by the upper lip. Manatees may also use their flippers to dig up the roots of these plants. This variable diet is most likely necessary to meet their nutritional demands. Some manatees may also eat invertebrates and will eat fish both in captivity and in the wild.
Because of the low nutritional value of the plants consumed, manatees must graze for 6 to 8 hours a day. Each day they consume 5-10 percent of their body weight, which can be over 100 kg in a large individual. This low-nutient diet also has also contributed to the the development of low metabolic rates. Manatees can survive on 25% percent less energy than a typical mammal of similar size.
Manatees feed on abrasive plants and, as a result, their molars are continually replaced throughout life as they wear down. Hind-gut fermentation is another adaptation to the herbivorous diet of the manatee, aiding in breaking down the cellulose of the plants eaten.
(FPL 1989, Nowak 1999, Rathbun 1990)