Manatees are herbivores that eat aquatic plants, spending six to eight hours a day grazing on seagrasses, freshwater vegetation, and floating plants. A typical manatee consumes about one-tenth of its body weight daily, which means a 1,000-pound adult eats roughly 100 pounds of plant matter every day. Their diet shifts depending on whether they live in saltwater, freshwater, or brackish environments, but plants make up nearly all of it.
Seagrass: The Staple Food
In coastal and estuarine waters, seagrass is the foundation of the manatee diet. Florida manatees graze heavily on species like manatee grass and shoal grass, which grow in shallow beds along the coastline. These underwater meadows are so important that their decline directly threatens manatee survival. When seagrass beds in Florida’s Indian River Lagoon deteriorated in recent years, hundreds of manatees starved, prompting wildlife agencies to consider emergency supplemental feeding with romaine lettuce.
Manatees don’t just nibble the tops of seagrass. They uproot entire plants, consuming blades, roots, and sediment along with them. This makes their diet highly abrasive, which has shaped their anatomy in remarkable ways.
Freshwater Plants
Manatees that spend time in rivers and springs eat a wider variety of vegetation. In Crystal River, Florida, hydrilla (an invasive aquatic weed) makes up about 80% of the available plant biomass and serves as the primary food source for manatees wintering there. They also eat water hyacinth, water lettuce, coontail, Eurasian watermilfoil, southern naiad, and tape grass.
Floating plants like water hyacinth and water lettuce require more effort to eat than submerged vegetation, since manatees have to manipulate them at the surface before pulling them underwater. Submerged plants are simpler to graze on, and manatees tend to eat them more efficiently. In areas where invasive freshwater plants dominate, manatees can actually help control their spread, though not nearly enough to serve as a biological management tool on their own.
How Manatees Eat
Manatees have an unusual feeding apparatus. Their upper lip is split into two muscular pads covered in stiff, whisker-like bristles. These bristles aren’t just sensory organs. They function like fingers, grasping and manipulating plants with surprising precision. Manatees use these bristle fields in a prehensile way, wrapping them around vegetation to pull it into the mouth. The technique changes depending on the food: when eating submerged plants, they use the bristles differently than when feeding on floating vegetation at the surface.
This flexibility makes manatees effective generalist feeders. They can forage in murky water where visibility is near zero, relying on their bristles to locate and handle food entirely by touch.
Teeth Built for a Tough Diet
Eating sandy, gritty plants all day would grind down most animals’ teeth permanently. Manatees solved this problem with a system found in no other mammal except elephants (and even then, differently). New molars continuously form at the back of the jaw and slowly migrate forward, pushing worn-out teeth ahead of them until the old ones fall out at the front. A manatee maintains a row of six to eight functional molars at any given time, with fresh replacements always in the pipeline.
This “conveyor belt” tooth replacement evolved specifically because of the abrasive, fibrous plants manatees eat. The forward movement of each tooth is made possible by constant remodeling of the jawbone itself, with bone dissolving in front of each tooth and rebuilding behind it.
Digestion and Metabolism
Despite eating large quantities, manatees run on a surprisingly slow metabolism for their size. They are hindgut fermenters, meaning they break down plant cellulose in the large intestine (similar to horses) rather than in a multi-chambered stomach like cows. Perpendicular folds in the large intestine trap food particles, giving gut bacteria extra time to extract nutrients. This makes manatees remarkably efficient at pulling nutrition from a food source that is, by mammalian standards, pretty low in calories.
Their low metabolic rate is one reason manatees are so sensitive to cold water. They simply don’t generate enough internal heat to tolerate temperatures below about 68°F (20°C), which is why they crowd into warm-water refuges like natural springs and power plant outflows during winter.
How Manatees Stay Hydrated
Living in saltwater creates a hydration challenge for any marine mammal. Manatees handle it by taking advantage of every freshwater source available. River mouths that stream drinkable water into coastal areas serve as critical drinking spots. During rainstorms, fresh rainwater collects on the ocean surface because it’s lighter than saltwater, and manatees will rise to the surface to vacuum it in.
Their food also provides significant water. Many aquatic plants are highly water-concentrated, so grazing doubles as hydration. On top of that, manatees produce water internally as a byproduct of digesting food, the same metabolic water production that helps desert animals like kangaroo rats survive without drinking. Between food moisture, opportunistic freshwater drinking, and metabolic water, manatees piece together enough hydration to thrive in salty environments.
Do Manatees Ever Eat Animals?
Manatees are classified as strict herbivores, but the picture is slightly more complicated. As they graze on vegetation, they inevitably swallow small invertebrates clinging to the plants: snails, tiny crustaceans, insect larvae, and similar organisms. This incidental intake may actually provide a meaningful source of animal protein, even though it’s not deliberate.
More surprisingly, a small population of manatees off the coast of Jamaica was observed eating small fish caught in gill nets. Fishermen watched through water glasses as manatees pulled fish into their mouths, chewed off the flesh, and left the skeletons tangled in the nets. Captive manatees at Marineland of Florida have also been fed small amounts of dead fish to supplement their lettuce diet. These are rare, opportunistic behaviors rather than a normal part of the manatee diet, but they show that manatees are capable of digesting animal matter when the opportunity arises.