Question

When one reads about fish and marine mammals, it is always said that for example blubber of marine mammals helps them with buoyancy because it is so low density and similarly for example sharks have large low density liver (possibly up to 30% of their body mass) and mainly cartilage that is about half the density of a normal bone (and it is implied this is necessary for buoyancy).

However, many terrestrial mammals like humans are already positively buoyant when having lungs filled with air (most humans in their normal weight), so it is not obvious why any kind of adaptions for marine animals are necessary as their body density composition could a priori be essentially just that of humans. There thus has to be a factor which makes it beneficial for e.g. marine mammals to have more something denser in relation to humans (like bigger muscles in relation to lower density tissue) which then needs to be compensated with such things as blubber. I am looking for what that factor is exactly.

Answer 1

Factors such as heat retention and buoyancy explain why marine mammals have adaptations for higher density compared to humans.

Step-by-step explanation:

Factors that make it beneficial for marine mammals to have a higher density than humans

Marine mammals, such as whales, have adaptations that allow them to survive in cold water environments. One important factor is maintaining their body temperature. Marine mammals have veins and arteries that are close together, allowing for efficient heat exchange. They also have thick layers of blubber to prevent heat loss. These adaptations require the marine mammals to have a higher density compared to humans, as blubber is denser than other tissues in the body.

Another factor is buoyancy. Although humans are buoyant when their lungs are filled with air, marine mammals need to stay buoyant in water. The large size and low density of the liver in sharks, and the presence of blubber in marine mammals, help them achieve buoyancy. By having more dense tissues, such as muscles, compared to humans, marine mammals can offset the buoyancy caused by their lungs being filled with air.

Overall, the high density and specific tissue composition of marine mammals, like blubber and large livers, are adaptations that help them regulate their body temperature and achieve buoyancy in cold water environments.

Answer 2

Marine mammals and fishes have specialized adaptations, such as blubber and cartilaginous skeletons, for buoyancy and thermoregulation in water. While terrestrial mammals may float due to lungs, marine animals require additional adaptations to remain neutrally buoyant and efficiently regulate their internal environment.

Step-by-step explanation:

Marine mammals, such as whales, and certain fishes, like sharks, possess adaptations for buoyancy and thermoregulation that differ significantly from those of terrestrial animals.

For instance, blubber plays a crucial role in insulating these marine animals from the cold water, and its low density aids in buoyancy.

Furthermore, blubber is metabolically active, storing energy that can be utilized during fasting periods.

This contrasts with terrestrial mammals, which may rely on thick fur and hibernation for warmth and slow metabolism during cold periods.

In terms of structural adaptations, sharks have a skeleton composed primarily of cartilage, which is about half the density of bone. This structural characteristic, together with a large, low-density liver that can constitute up to 30% of their body mass, contributes to their buoyancy.

In contrast, terrestrial mammals like humans often have natural positive buoyancy due to air-filled lungs; however, marine animals need these additional adaptations to remain neutrally buoyant, enabling them to maintain their position in the water column without expending energy on constant swimming.

Countercurrent heat exchange systems in marine mammals and the osmoregulatory adaptations of fish, allowing them to balance salt and water in various aquatic environments, are other examples of specific adaptations for marine life.

These physiological mechanisms, combined with specialized features like the swim bladders of bony fish or the urea and TMAO retention in sharks for osmotic balance, illustrate the complexity of adaptations required for life in the marine environment as opposed to on land.