The dugong, Dugong dugon, is a large, gentle marine mammal found in the warm coastal waters of the Indo-Pacific region. It is the only strictly herbivorous marine mammal, earning it the common nickname “sea cow” due to its slow, methodical grazing behavior. Belonging to the order Sirenia, the dugong shares its lineage with manatees, but remains exclusively in saltwater environments. This aquatic grazer can grow up to three meters in length and weigh over 400 kilograms, sustained entirely by plants.
The Primary Food Source: Seagrass
The dugong’s diet is dominated by seagrass, though they show a strong preference for certain types that offer the best nutritional payoff. These preferred species are typically fast-growing pioneer species that are low in structural fiber.
Specifically, dugongs target seagrasses from the genera Halophila and Halodule, such as Halophila ovalis and Halodule uninervis. These plants have a high content of nitrogen and are easily digestible, allowing the dugong to maximize nutrient intake. Their chemical composition, including higher levels of crude protein and starch, supports the large body size and metabolic needs of the marine mammal. An adult dugong consumes a substantial amount of vegetation daily, sometimes between 25 and 40 kilograms of wet weight seagrass.
Specialized Foraging Behavior
The dugong possesses a physical anatomy adapted for harvesting its submerged food source. Its large, downturned snout and thick, bristly lips are designed for foraging along the seabed. This unique mouth structure allows the animal to effectively grasp and manipulate seagrass plants growing close to the sediment.
The primary feeding action is called “excavation” or “grubbing,” where the dugong roots into the substrate rather than simply cropping the leaves. They use their prehensile lips to dig up and ingest the entire plant, including the nutrient-rich underground stems known as rhizomes. This rooting behavior leaves behind distinct, continuous furrows or “feeding trails” on the seafloor.
Dugongs often prioritize the energy-dense rhizomes found beneath the surface, though they can crop the leaves of taller seagrass. This comprehensive harvesting technique contrasts with the simple grazing of other marine herbivores. The choice between excavation and cropping can also be influenced by perceived danger, as rooting makes them less aware of approaching predators.
Dietary Context and Habitat Dependency
The dugong’s reliance on seagrass dictates its ecological distribution, restricting it to coastal habitats that can support its demanding diet. Dugongs are found predominantly in shallow, protected tropical and subtropical waters where extensive seagrass meadows thrive. These areas include wide bays, lagoons, and inter-reefal waters that provide both the food source and a sheltered environment.
Although seagrass constitutes nearly the entirety of their diet, small deviations occur. Dugongs occasionally ingest algae, which may become more significant when seagrass is scarce. Very small invertebrates, such as polychaete worms or shellfish, may also be consumed accidentally when the dugong excavates the seagrass roots.
This specialized diet links the animal’s survival directly to the health of the seagrass ecosystems, creating vulnerability to habitat degradation. Human activities like coastal development, dredging, and pollution introduce sedimentation and poor water quality that destroy seagrass beds. The resulting food shortages impact dugong health and reproductive success, making the loss of foraging grounds a serious threat globally.