Manatees are gentle, slow-moving aquatic mammals belonging to the order Sirenia, often nicknamed “sea cows.” They are obligate grazers whose diet consists almost entirely of plant matter. This specialized herbivorous lifestyle dictates their anatomy, behavior, and geographical distribution. They spend a significant portion of their day foraging in the shallow, plant-rich waters they inhabit, relying on a diet of low-calorie, fibrous aquatic vegetation.
The Manatee’s Strict Vegetarian Menu
Manatees are non-ruminant herbivores that rely on continuous grazing to sustain their large body mass. Due to the low nutritional density of aquatic plants, they consume an enormous volume of food daily, typically 10 to 15 percent of their body weight in wet vegetation. An adult manatee consumes up to 100 to 200 pounds of food daily, often grazing for seven hours or more.
The specific menu varies depending on whether the manatee is in a marine or freshwater environment. In saltwater, their diet is dominated by seagrasses, including species like turtle grass, manatee grass, and shoal grass. They also consume marine algae and the leaves of mangrove trees.
When manatees move into freshwater rivers and springs, their diet shifts. They have been observed consuming over 60 different species of plants, demonstrating an opportunistic approach to aquatic foraging. They use their front flippers to guide vegetation toward their highly flexible, prehensile lips, which are adapted for tearing plants. Freshwater plants include:
- Hydrilla
- Water hyacinth
- Water lettuce
- Eelgrass
Physical Adaptations for a Plant-Based Diet
The manatee’s body is adapted for processing massive quantities of abrasive, cellulose-rich food. One unique feature is their dental structure, often referred to as “marching molars.” Unlike most mammals that replace teeth vertically, manatees replace their molars horizontally and continuously throughout their lives.
As the front molars wear down from grinding tough, sand-coated plants, they are shed. New molars emerge at the back of the jaw and slowly migrate forward to take their place, ensuring a constant supply of fresh grinding surfaces. This continuous replacement counteracts the high rate of wear caused by their abrasive diet.
Digesting fibrous plants requires a specialized internal system, which in manatees is a form of hind-gut fermentation. They possess an extremely long digestive tract, measuring around 145 feet in length. This extensive gut allows for the necessary time and space for symbiotic microbes to break down the tough cellulose found in aquatic vegetation. This slow digestive process, which can take about seven days, is supported by their naturally slow metabolism, helping them maintain their body temperature and survive on a low-energy diet.
Why Their Diet Matters to Conservation
The manatee’s reliance on a vast, steady supply of aquatic plants directly links its survival to the health of its habitat. Manatees depend on extensive, shallow-water seagrass meadows for their primary food source. The destruction of these seagrass beds due to pollution, dredging, and runoff creates significant food limitation challenges. Nutrient pollution from urban and agricultural runoff fuels harmful algal blooms that block sunlight, leading to seagrass die-off and subsequent starvation. Furthermore, their need to graze in shallow waters makes them vulnerable to boat strikes, which are a leading cause of direct human-related deaths.