Manatees are large, fully aquatic mammals that inhabit warm, shallow coastal waters and rivers across the globe. They are herbivores, often referred to as “sea cows,” sustained by a diet composed almost exclusively of plants. Their immense size and gentle nature are maintained by this diet. The constant need for energy to maintain their body temperature means that grazing is a fundamental biological imperative for their survival.
The Mainstay of the Manatee Diet
Manatees sustain themselves on a wide variety of aquatic plants found in both freshwater and marine environments. Their diet comprises over 60 different species of submerged, floating, and emergent vegetation. In saltwater habitats, the diet is dominated by seagrasses. Specific marine plants consumed include turtle grass, manatee grass, and shoal grass, which grow in the shallow, sunlit coastal zones they frequent.
In freshwater sources, manatees consume plants such as hydrilla, water hyacinth, and water lettuce. These species, along with freshwater algae, provide the roughage necessary for their diet. Because the plant material they consume is low in nutritional density, they must consume enormous quantities to meet their daily energy demands.
How Manatees Find and Consume Food
An adult manatee must consume between 10 to 15 percent of its body weight in wet vegetation every day. This translates to eating well over 100 pounds of plants daily. Manatees dedicate up to seven hours a day to foraging to process this volume of food.
Physical adaptations aid in constant grazing, beginning with a large, flexible, and prehensile upper lip that is split down the middle. This split lip, controlled by seven muscles, allows the manatee to grasp, tear, and manipulate vegetation with precision. They also use their front flippers to help pull or scoop plant material toward their mouths.
Once the vegetation is inside, it is pressed against dense, horny ridged pads on the roof of the mouth. These pads, along with the lower jaw, initially tear the food before it is sent back for grinding molars.
The constant chewing on tough plant matter requires a unique dental adaptation known as “marching molars.” New molars continuously grow at the back of the jaw and slowly move forward to replace the older, worn-down teeth at the front. This replacement system allows them to grind the fibrous material they consume. Furthermore, their large intestinal tract, which can be up to 150 feet long, is responsible for the hindgut fermentation process that breaks down high levels of cellulose.
Regional Dietary Differences and Accidental Intake
While the West Indian manatee relies heavily on seagrass, the Amazonian manatee has a different diet reflecting its purely freshwater habitat. These riverine manatees consume aquatic macrophytes like water hyacinths and grasses. They also incorporate floating fruits and leaves that drop into the water from overhanging trees, demonstrating an opportunistic feeding behavior.
A significant, though non-nutritive, part of the manatee’s intake is the accidental ingestion of sand, small rocks, and shells. This occurs because manatees often graze along the bottom, uprooting plants and scooping up the substrate in the process. The abrasive, gritty nature of this consumed material contributes to the rapid wear of their teeth. This unintentional intake of grit also plays a role in aiding the grinding of the tough plant material during the initial stages of digestion.