Sea Otters and their Metabolisms

In ecosystems all over the world we see animals who have adapted to their environments; whether they are finches that Darwin noted as having specialized beaks to consume certain seeds or if they are organisms that shed their coats in the spring to make the summer heat a little more bearable. Either way, animals adapt to their surroundings and have learned to be plastic to survive on this planet. One creature that stood out to me as possessing an interesting way of adapting is the Sea Otter. 

Sea Otters are semi-aquatic (going to shore only when necessary) spending most of their time in the frigid ocean waters. Due to the constant exposure to the elements, Sea Otters have adapted slower metabolism and respiration rates as well as dense fur coats able to minimize their energy expenditure in their routine lives. So, how exactly do Sea Otters adapt to the aquatic environments?

When most terrestrial organisms are submerged in a pool of cold water or are engulfed in cold air, their bodies shiver in an attempt to produce heat because their metabolisms are working faster than they can consume anything worth storing. In the case of the Sea Otter, this is a similar problem; however, these creatures have adapted a unique way of preventing their produced energy from going out the window. Deep inside an Otter lays its metabolism, a set of chemical reactions which help the organism to respond to its environment. This set of reactions also helps break down compounds, which make up its food, as well as aiding in the chemicals produced and needed for respiration. Though these two concepts, metabolic rates and respiration, do not seem linked, the Sea Otter has found a way to interlink the two with its physiological adaptations. One way this semi-aquatic creature accomplishes this is by lowering its consumption of O₂ and CO₂ when submerged in the water. The metabolic rate of Sea Otters at rest is recorded as 13.50 +- 1.81 mL O₂/ 12.05 +- 0.13 mL CO₂. The submerged metabolic rates are recorded as 17.55 +- 1.70 mL O₂ as compared to the surface swimming metabolic rates of 29.61 +- 1.60 mL O₂ which represents a 41% decrease in the metabolic rate.

The paper entitled, "Swimming by sea otters: adaptations for low energetic cost locomotion" by Terrie M. Williams discusses a study done on otters to better understand whether the metabolic changes that the animals go through are actually beneficial and significant enough to call them "changes". 

In order to test this idea, otters were studied swimming both on the surface and submerged. While the otters swam, they were videotaped and their movement (number and frequency of strokes, alternation of paddling limbs, speed, etc) were documented. The distance in which each otter swam was also documented. For the metabolic aspect of this endeavor, the oxygen consumption, carbon dioxide production and respiratory quotient (relative to body size) was recorded. These recordings were taken from otters that were doing various levels of work: resting, grooming and swimming. A chamber that replicated still water and moving current were provided for the otters and each one was tested swimming up current in the chamber. 

After vigorous testing, it was found that the otters were taking in more oxygen with the more work they were doing, as well as exerting more carbon dioxide; however, there was a dramatically lower amount of oxygen input and carbon dioxide output when the otters dove under the water. This data was able to support part of the original question of whether there was a significant change in the metabolism of this sea animal. 

Williams, Terrie M. "Swimming by Sea Otters: Adaptations for Low Energetic Cost Locomotion." Journal of Comparative Physiology A 164.6 (1989): 815-24. Print.