The Amazonian manatee (Trichechus inunguis) is a large, aquatic mammal found exclusively within the vast freshwater network of the Amazon Basin. Sometimes called a “cowfish” in Brazil, this gentle creature is the smallest of the three extant manatee species. It navigates the slow-moving rivers, floodplains, and lakes, playing an important part in its unique ecosystem.
The Herbivorous Diet of Amazonian Manatees
The Amazonian manatee maintains an exclusively herbivorous diet, consuming a wide array of aquatic plants. Its grazing habits help manage the growth of aquatic vegetation, influencing the health and balance of the waterways. Manatees consume a substantial amount of plant matter daily, typically around 8% of their body weight. A 300-kilogram manatee, for instance, might consume about 30 kilograms of macrophytes each day.
Key Aquatic Plants in Their Diet
The diet of Amazonian manatees is diverse, encompassing over twenty species of aquatic plants, including grasses, leaves, and submerged vegetation. Water hyacinths (Eichhornia crassipes) and water lettuces (Pistia stratiotes) are commonly consumed and form a significant portion of their diet. They also feed on various types of aquatic grasses, such as Paspalum repens and Echinochloa polystachya. Other plant species in their diet include aroids, bladderworts, hornworts, and water lilies.
Manatees also consume palm fruits that fall into the water, adding to their varied plant-based intake. Their diet can shift seasonally, with greater diversity during lower water levels when food is scarcer. During the wet season, when plant growth is abundant, their diet may become more selective. The presence and abundance of these plants directly influence the manatees’ feeding patterns and movements.
How Manatees Forage and Adaptations
Amazonian manatees possess physical adaptations for their plant-based diet. They use their flexible front flippers and large, prehensile upper lips to grasp and tear off vegetation. Their lips move independently for efficient food manipulation. A unique dental adaptation is their continuously replaced molar teeth, which migrate forward in the jaw throughout their lives, helping to grind tough plant fibers.
Their digestive system, similar to that of a horse, is post-gastric and highly efficient at processing plant matter. This, combined with a low metabolic rate, allows them to survive periods of reduced food availability. During the dry season, when water levels drop and vegetation becomes scarce, Amazonian manatees can fast for weeks or even months by relying on their substantial fat reserves.