Manatees, often referred to as sea cows, are large, fully aquatic marine mammals classified in the order Sirenia. They are obligate herbivores, meaning their diet consists almost exclusively of aquatic plants. This specialized diet drives their behavior, physiology, and habitat selection. The sheer volume of plant material they must consume daily to sustain their immense size is a defining feature of their survival.
The Primary Diet of Aquatic Plants
Manatees consume a wide variety of vegetation, encompassing over 60 different species found in both marine and freshwater environments. In saltwater habitats, their diet centers on seagrasses, which are flowering plants that grow in dense underwater meadows. Staple items include turtle grass (Thalassia testudinum), manatee grass (Syringodium filiforme), and shoal grass (Halodule wrightii).
Seagrasses are fibrous and low in nutritional value, necessitating the consumption of substantial quantities. In freshwater systems, manatees shift their focus to aquatic weeds and submerged plants. Common foods in these areas include hydrilla (Hydrilla verticillata), water hyacinth, and water lettuce.
They also consume emergent and shoreline vegetation, such as mangrove leaves and fallen fruit or acorns along the banks. This adaptability allows them to forage successfully across the brackish estuaries, rivers, and coastal waters they inhabit.
Manatee Feeding Habits and Daily Intake
A manatee’s feeding routine is a continuous, lengthy process, reflecting the low caloric density of their plant-based food sources. They typically spend between six and eight hours each day actively grazing to meet their nutritional demands.
Manatees ingest anywhere from 7% to 15% of their total body weight in wet vegetation every 24 hours. For a large adult weighing 1,000 pounds, this means processing approximately 70 to 150 pounds of aquatic plants daily.
They employ their flexible, prehensile lips, which are split down the middle, to grasp and manipulate plants. Their front flippers are also used to help guide vegetation toward their mouths or to anchor themselves while foraging. Before the food reaches the grinding molars, tough, horny pads on the roof of the mouth and lower jaw crop and tear the fibrous material into smaller pieces.
Specialized Digestive Anatomy
The fibrous, low-nutrient diet requires specialized biological machinery to extract sufficient energy. Lacking front teeth, manatees rely on a unique dental system known as “marching molars” for continuous grinding. These molars are continuously replaced throughout the manatee’s life in a horizontal fashion, with new teeth forming at the back and moving forward as the older, worn teeth fall out.
This constant replacement, or polyphyodonty, is an adaptation to the high rate of wear caused by chewing tough, silica-rich aquatic plants and ingesting grit. Manatees are classified as hindgut fermenters, meaning the majority of nutrient extraction occurs far down the digestive tract. Their voluminous digestive system, including an intestine that can stretch up to 150 feet, provides a large fermentation chamber.
Symbiotic microorganisms within the hindgut break down the complex cellulose in the plant cell walls. This digestive process is slow, taking approximately seven days to pass through the entire system. This lengthy retention time maximizes the opportunity for microbial fermentation to yield the necessary nutrients from a low-quality food source.
Dietary Differences Across Habitats
The composition of a manatee’s diet varies significantly based on whether they inhabit marine, estuarine, or freshwater environments. Manatees in purely marine or coastal habitats, such as those in Belize and Puerto Rico, obtain the vast majority of their sustenance from seagrasses. Their entire diet can sometimes be composed of these saltwater plants, which are readily available in warm, shallow coastal waters.
In contrast, manatees that frequent freshwater systems, such as the upper reaches of Florida rivers, consume a higher proportion of aquatic weeds like hydrilla and water hyacinth. Stable isotope analysis confirms this regional variation, showing that some populations rely predominantly on freshwater vegetation while others are dependent on seagrass meadows. The movement of manatees between these water bodies, often driven by seasonal temperature changes, necessitates a flexible diet.