Creature Feature: Manatees

Many of us have slowed down our fast-paced lives during the pandemic, so it’s hard to recall how differently we lived last year. The morning grind to beat rush hour traffic, the hurried meal we scarfed down during our brief lunch break, the rushed exercise routine we somehow managed to squeeze in on our way home from work. Humans live hastily. This year, we had to slow down. We paused. Some of us no longer had to drive to work. Some of us even had time to prepare breakfast, lunch, and dinner every day for the past few months. As I sat down to think about what creature was emblematic of human experience this year, I realized that most of the animals around us have continued their daily routines. Buffalo move from feeding ground to watering hole, preying mantids stalk their prey, and dolphins ride waves in perfect coordination. However, one creature, universally acknowledged to live life slowly, stands out among the frenzy: the manatee (genus: Trichechus).

Manatees use their front and hind flippers to propel themselves forward through the water column. Photo by Robert Bonde/USGS [source].

These aquatic mammals are never in a rush. In fact, they are even colloquially known as sea cows. Contrary to popular belief, manatees are more closely related to elephants than they are to marine mammals like whales. Unlike their marine mammal counterparts, they move through life at a languid pace, typically swimming at speeds around 0.06–1.14 meters per second [1]. To put this in perspective, the average human walking speed at crosswalks or intersections is about 1.4 meters per second. There are three recognized manatee species, ranging in different parts of the globe including the east coast of Northern America (Trichechus manatus), the west coast of Africa (Trichechus senegalensis), and the Amazon River (Trichechus inunguis) [2]. Most research on manatees comes from the subspecies located around the coast of Florida. All three species tend to inhabit shallow tropical waters where they feed on submerged aquatic plant and algae species [3]. Although they are exclusively water-dwelling, manatees cannot breathe under water. So, like all marine mammals, they must constantly surface to breathe. Observational studies indicate that manatees can remain submerged for nearly 20 minutes [3]. Perhaps the slow swimming speeds help them preserve oxygen as they forage leisurely along sea beds.

Manatees are herbivorous aquatic mammals and have a diet composed exclusively of plants found submerged under water. Photo by Fritz Geller-Grimm [source].

Manatees, like other aquatic mammals, have adapted to the constraints of underwater living. They have adaptations for diving, navigation, thermoregulation (maintaining a relatively constant internal temperature), and osmoregulation (regulation of salt and water concentration in the body) [4]. Perhaps one of the most fascinating of these behaviors is their ability to control their buoyancy through gas compression. Manatees have a bizarre diaphragm morphology, that muscular component in mammal bodies that plays an important role in breathing [4]. Human free divers often regulate their breathing before long dives by controlling the amount of air in their lungs. Since manatees must often remain submerged for far longer, they have adapted to this particular constraint by relying on another type of gas: flatulence. That’s right, researchers believe that manatees rely on the gas produced by their massive intestines to adjust their dive depths [4]. In other words, they fart…to control their buoyancy. This unique adaptation makes use of the immense volumes of methane produced by the bacteria in their gut that ferment all those aquatic grasses and plants. So, as we wrap up 2020, putzing around our homes in pajamas and ambling through life, remember the manatee the next time you let one rip…and imagine drifting in altitude with each burst of wind. I promise, it’ll make you smile every time.


References

  1. Kojeszewski, T. & Fish, F. E. (2007). Swimming kinematics of the Florida manatee (Trichechus manatus latirostris): hydrodynamic analysis of an undulatory mammalian swimmer. Journal of Experimental Biology210(14), 2411–2418.
  2. Vianna, J. A., Bonde, R. K., Caballero, S., Giraldo, J. P., Lima, R. P., Clark, A., . . . & Rodríguez‐Lopez, M. A. (2006). Phylogeography, phylogeny and hybridization in trichechid sirenians: implications for manatee conservation. Molecular Ecology15(2), 433–447.
  3. Reynolds III, J. E. (1981). Behavior patterns in the West Indian manatee, with emphasis on feeding and diving. Florida Scientist, 233–242.
  4. Rommel, S. & Reynolds III, J. E. (2000). Diaphragm structure and function in the Florida manatee (Trichechus manatus latirostris). The Anatomical Record: An Official Publication of the American Association of Anatomists259(1), 41–51.

Main photo by Ramos Keith/USFWS [source]

Edited by Jessica Schaefer

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