In the cold expanse of the ocean, size and bulk are closely tied to survival. For many of the planet’s largest aquatic animals, what appears as “fat” is a highly specialized adaptation. This layer of tissue enables creatures to navigate vast distances, endure frigid temperatures, and survive long periods without food.
The Function of Blubber
Blubber is a specialized, thick layer of adipose tissue intertwined with collagen fibers, found directly beneath the skin of many marine mammals. This tissue is heavily vascularized, meaning it is rich in blood vessels, which distinguishes it from the fat in terrestrial animals. Its composition is not uniform; the fatty acid profile changes from the inner layer to the outer layer, with the inner layer being more metabolically active while the outer layer is more structural.
The primary role of this tissue is thermoregulation. Water conducts heat away from the body about 25 times faster than air, making heat retention a significant challenge for warm-blooded animals. Blubber provides powerful insulation against the cold, with its effectiveness determined more by lipid concentration than sheer thickness. Blood vessels within the blubber can constrict in cold water to reduce blood flow to the skin, minimizing heat loss.
This subcutaneous layer also serves as an energy reserve. Marine mammals like whales and seals undertake long migrations or endure extended fasting periods, metabolizing the fat stored in their blubber for energy. Furthermore, because fat is less dense than water, blubber provides buoyancy, helping these large animals float with less effort and streamlining their bodies for more efficient movement.
Marine Mammals Known for Their Size
Whales, such as the blue whale and humpback whale, possess an immense blubber layer that can be over 30 cm thick. This layer is not just for insulation in polar waters but is also the fuel tank for some of the longest migrations on Earth. A blue whale may fast for several months, relying almost entirely on its fat stores to power its journey between feeding and breeding grounds.
Pinnipeds, a group that includes seals and walruses, depend on their blubber to survive in frigid polar and subpolar environments. Their blubber allows them to maintain a stable body temperature whether in icy water or on land. The thickness of this layer can vary based on age, health, and season. Walruses, in particular, have exceptionally thick skin and blubber to withstand the harsh Arctic conditions.
In contrast, sirenians like manatees and dugongs are a different case. Despite their large, rounded bodies, they have a low percentage of body fat compared to other marine mammals. Their bulk comes from their large gastrointestinal tract for digesting a plant-based diet. Lacking a thick, insulating layer of blubber, manatees are susceptible to cold stress and must remain in warm waters.
Unconventional “Fat” Fish
Beyond mammals, other sea creatures have a “fat” appearance for different reasons. The ocean sunfish, or Mola mola, is one of the world’s heaviest bony fish, with some individuals weighing over 2,300 kg. Its immense size and round, truncated shape give it a bulky look, but this is not due to blubber. The sunfish’s body is supported by a skeleton of cartilage and has a thick subcutaneous gelatinous layer that helps it achieve neutral buoyancy.
The blobfish gained internet fame for its drooping appearance, but this look is a misleading artifact of its journey from the deep sea. In its natural habitat between 600 and 1,200 meters, extreme water pressure gives its body a conventional fish-like shape. To survive this pressure, the blobfish’s body is a gelatinous mass with a density slightly less than water. This allows it to float above the seafloor with minimal energy expenditure. When brought to the surface, rapid depressurization causes its tissues to expand and lose structural integrity.