Dugongs are seagrass specialists feeding on only a few species of tropical seagrasses in any part of their range. When they feed, they usually dig up the entire seagrass plant if the seagrasses are small, e.g. Halophila ovalis and Halodule uninervis, leaving distinctive feeding trails through the seagrass bed. When feeding on longer-leaved seagrasses such as Syringodium isoetifolium, dugongs ingest the leaves only.

Halophila ovalis: dugong's favourite food	Feeding trail

 

Feeding dugong

 

The head and mouthparts of the dugong are unusual. The strangely- shaped skull of the dugong has a prominent down-turned anterior region so that the mouth is located ventrally. External features of the mouth include a large disc-shaped rostrum and strong prehensile lips. Dugongs feel for seagrasses in muddy waters using extra-sensitive hairs on the rostral disc, and then grasp and uproot seagrasses using their lips. The cheekteeth (premolars and molars) of the dugong are small, soft and peg-like and become largely non-functional as a dugong ages. Dugongs rely on large internal mouth-pads to ingest and macerate seagrasses. Dugongs are able to consume huge quantities of seagrass during a single dive- they create feeding trails of up to 8 m in length and up to 20 cm width with removal of >70% of seagrass during dives of about 1 minute. Rather than stopping to chew, dugongs choose seagrasses that are low in fibre and break up easily as they are pulled into and through the mouth.

Dugong head showing rostral disc and prehensile lips

 

Like most other marine mammals, dugongs are long-lived, give birth to one calf at a time and the females invest a lot of time and energy into each offspring. However, the breeding cycle of the dugong is probably protracted compared to almost all other marine mammals. In most parts of their range, dugongs reach sexual maturity in their teens (13-17 y for females) and then mate and give birth every 5-7 years. In comparison, manatees have calves every 2-3 years. We think that the slow growth and low and variable breeding rate of the dugong is probably due to the dugong's narrow and nutrient-poor seagrass diet. We have evidence that the metabolic rate of the dugong may be quite high compared to a manatee so that a dugong may have high nutrient and energy requirements that are difficult to meet.

Dugong skull

Dissected head of dugong showing positions of cheekteeth and horny pads