Manatees are massive marine mammals and obligate herbivores, meaning their diet consists almost exclusively of plant matter. Manatees primarily consume seagrass and various freshwater plants. They generally do not eat true seaweed, also known as marine algae, as their main food source. This preference is rooted in their digestive adaptations and the ecological availability of their preferred vegetation.
The Manatee’s Primary Diet: Seagrass and Aquatic Plants
Manatees are opportunistic herbivores, feeding on more than 60 different species of plants. In saltwater environments, the foundation of their diet is seagrass, a true flowering plant that forms dense meadows in shallow, coastal areas. Important food sources include Turtle Grass, Manatee Grass, and Shoal Grass.
When manatees move into freshwater habitats, such as rivers, springs, and canals, their diet shifts to available aquatic plants. These include common species like hydrilla, water hyacinth, water lettuce, and eelgrass. They may also consume parts of shoreline vegetation, such as mangrove leaves, by reaching out of the water.
Manatees may occasionally ingest small invertebrates or fish accidentally while grazing. This is not an intentional part of their feeding strategy, as they are not adapted to hunt or consume animals. The variety of plants they consume depends heavily on their location and the season.
Defining the Difference Between Seaweed and Seagrass
The biological distinction between seaweed and seagrass explains the manatee’s dietary preference. Seagrass is a true flowering plant, complete with roots, stems (rhizomes), and leaves (blades). Its roots anchor it firmly into the soft sand or mud, and it possesses vascular tissues to transport nutrients.
In contrast, seaweed is marine macroalgae belonging to a different biological kingdom, not a true plant. Seaweed lacks true roots, stems, and flowers. It anchors itself to hard surfaces using a structure called a holdfast, which serves only as an anchor. Algae absorb nutrients directly from the surrounding water, unlike seagrass, which draws nutrients from the sediment.
Manatees are adapted to graze the rooted, blade-like structure of seagrass, which is a more substantial food source. They sometimes consume marine algae when their primary seagrass diet is scarce, but it is generally considered a substitute rather than a preferred staple. For example, studies showed an increase in algae consumption after a major seagrass die-off, indicating a shift to a survival food.
Manatee Feeding Mechanics and Consumption Rates
Manatees spend a considerable portion of their day foraging, grazing for up to seven hours daily to maintain their large body mass. They possess highly specialized feeding tools, most notably their prehensile lips. These lips are split in the middle and function like flexible, muscular pincers, used to grasp, pull, and tear off vegetation.
The manatee uses its front flippers to help guide vegetation toward its mouth while grazing. Horny, ridged pads on the roof of the mouth and lower jaw break the food into smaller pieces. The food is then ground by a continuous conveyor belt of molars that are constantly replaced as they wear down from the abrasive vegetation.
Due to the low nutritional density of aquatic plants, manatees must consume massive quantities of food each day. An adult manatee typically consumes between 10% and 15% of its body weight daily. For a 1,000-pound animal, this translates to about 100 to 150 pounds of wet vegetation consumed every 24 hours.