Once in a while we hear people talk about ecological imbalance, particularly often referring to the cold near-coastal environments where waves are bounced back by underwater forests, or kelp. At the “roots” of these 60 meter high brown macroalgae, the biodiversity does not cease to surprise us. Purple urchins are sparkled a bit here and there, red abalones slowly move around and feed on small invertebrates hidden in the substrate crevices, colourful starfish of all kinds explore the seafloor, and shells are home to octopuses. However enchanting it might seem, the magic only raises as one moves between the kelp “branches.” Small sharks sneakily move around, while sea otters, wrapped in macroalgae, relax at the surface.
Now, in this perfectly balanced environment, if one of the components is taken away, the system crashes like a cascade. For instance, when otters were hunted for fur between 1741 and 1911, their absence from kelp forests triggered their prey – purple urchins – to proliferate to such levels to eat everything on their way, including the bases of the kelp, and finally creating a desert, known as barren. But let’s not focus on the utter shitness of the human race for a moment.
In this blog post, we will be touching on some characteristics of sea otters (Enhydra lutris), so as to discover their special powers. They are the smallest carnivorous semi-marine mammals, not so elegant on land as they are in the sea. There is no need for them to set foot on land as they can close their nostrils and ears when sleeping. In fact, they sleep while floating on the water, wrapped up in kelp to keep adrift, thanks to their incredible lung capacity, that is 2,5-fold higher than that of mammals alike. Hence, they can also stay submerged for longer periods of time, holding their breath for up to 5 minutes.
They lack a thermo insulating fat layer but they have made their pelage waterproof through the production of a hydrophobic lipid called squalene. This not only keeps the cold water away but it also improves the body’s hydrodynamics.
Sea otters are elegant surface swimmers that thrust through the alternational strokes of the paired appendages, thus maneuvering precisely. While the rapid and submerged swimming to catch prey excludes the paddling and involves a locomotion more similar to marine mammals ad hoc, since the whole elongated body undulates dorsoventrally with just occasional assistance of the back or hind feet. The fore feet are meanwhile kept tight by the chest area. This type of swimming increases the acceleration, and therefore, improves the performance.
Sea otters can easily dive to the seafloor to forage for fish, crustaceans, sea urchins, bivalves and snails, that they incise with incisor teeth in order to eat out the content, or use rocks to open the hardest of shells. The most energy consuming hunt is the one on abalones, that are strongly attached to the substrate and need to be hit with a rock several times before removing them. Their foraging and hunting methods are mainly followed from those assumed by their mothers.
To close the circle of life, they are great prey to sea lions that oftentimes visit the kelp forests, and orcas that come close on rare occasions. The youngest individuals are also caught by eagles, when floating on the surface. Whenever sea otters start missing, this creates an obvious instability of the ecosystem, resulting in cascade effects that lead to changes beyond repair, which makes them the keystone species of the kelp forests.
There is something about sea otters that makes me smile whenever I come across documentaries or books about them. It might be their floating enjoyment or their swimming that seems like a dance, what do you think?
Williams, T.M., 1989. Swimming by sea otters: adaptations for low energetic cost locomotion. Journal of Comparative Physiology A, 164(6), pp.815-824.
Fish, F.E., 1994. Influence of hydrodynamic-design and propulsive mode on mammalian swimming energetics. Australian Journal of Zoology, 42(1), pp.79-101.
Watson, J., 2000. The effects of sea otters (Enhydra lutris) on abalone (Haliotis spp.) populations. Canadian Special Publication of Fisheries and Aquatic Sciences, pp.123-132.
Estes, J.A. and Palmisano, J.F., 1974. Sea otters: their role in structuring nearshore communities. Science, 185(4156), pp.1058-1060.