Manatees: Flatulence as a Diving Mechanism
The manatee is one of the most gentle marine mammals — and one of the most biologically fascinating with regard to intestinal gas. Unlike virtually all other animals, gas production in the manatee is not merely a byproduct of digestion but an actively used physiological mechanism for controlling buoyancy. Manatees control their diving depth by retaining or releasing intestinal gas — a principle reminiscent of a submarine's ballast tank.
The Manatee Body: Evolutionarily Oriented Toward Gas
Manatees are herbivores that eat up to 10% of their body weight in aquatic plants daily — in a full-grown animal, up to 50 kilograms of vegetation per day. This plant-based diet is fermented in the long digestive tract by gut bacteria, producing considerable amounts of methane, CO₂, and hydrogen. The manatee's digestive system is anatomically adapted for this task: they have an unusually long and muscular large intestine. But the decisive feature is the ability of the intestinal muscles to deliberately compress and store produced gas — or release it.
Buoyancy Control Through Intestinal Gas: The Submarine Principle
Marine biologists observed that manatees show significantly more gas release in shallow water and at the surface than in deep water. Conversely, manatees that want to dive can compress the gas in their intestines. The biological mechanism: the powerful intestinal muscles can increase or decrease the gas pressure in the gut, which directly affects the density of the body. Less gas in the intestine = higher body density = sinking. More gas = lower density = rising to the surface. This mechanism makes manatees one of the few animals that actively control their buoyancy through intestinal gas management. Lung size plays a complementary role — manatees have horizontally positioned lungs arranged along the back, which also contributes to buoyancy optimization.
Water Pollution and the Manatee Gas Problem
The manatee's buoyancy strategy has an unexpected vulnerability: pollutants. Pesticides and other organic contaminants found in waters inhabited by manatees can damage the gut flora and alter gas production. Manatees living in heavily polluted waters show altered gas production patterns according to studies by USF (University of South Florida) — which impairs buoyancy control. Individual animals have been observed struggling to stay at the water's surface — or conversely unable to dive normally. Since manatees must regularly surface to breathe, disrupted buoyancy control is potentially life-threatening.
Gas Production in Figures
Concrete measurements of manatee intestinal gas were first conducted in the 1970s by American marine biologists. Per kilogram of body weight, a manatee produces an estimated 3–5 mL of gas per hour — in a 600 kg animal, that equates to 1.8–3 liters of intestinal gas per hour. Over a day, this accumulates to a gas volume equivalent to a large wine bottle. This gas is, as in most herbivores, relatively odorless (low sulfur compounds), but has high methane concentrations depending on nutritional status. Manatees are, relative to their body size, efficient methane producers — but their contribution to atmospheric methane is negligible due to the small total population (approximately 13,000 animals worldwide).
Did you know?
- Manatees actively control their buoyancy by retaining or releasing intestinal gas — similar to a submarine.
- A 600 kg manatee produces an estimated 1.8–3 liters of intestinal gas per hour.
- Water pollution can damage the manatee's gut flora and impair buoyancy control.
- Manatees have lungs positioned horizontally along the back — another buoyancy mechanism.
Fun Fact
Zoologist Daryl Domning, a specialist in manatee evolution, described in an interview the first time he observed a manatee farting underwater: 'It was a large gas bubble that rose directly beneath my snorkel — the smell was surprisingly mild and reminded me of freshly cut grass. Then the animal surfaced. It had obviously just discharged its ballast.' Domning is one of the few people to have described the sound of a manatee fart underwater: 'A deep, water-muffled rumble.'
Sources
- Domning, D.P. & Hayek, L.C. (1986). Interspecific and intraspecific morphological variation in manatees. Marine Mammal Science, 2(2), 87–144.
- Reynolds, J.E. & Odell, D.K. (1991). Manatees and Dugongs. Facts on File Publications.
- Rommel, S.A. & Reynolds, J.E. (2000). Diaphragm structure and function in the Florida manatee. Anatomical Record, 259(1), 41–51.