Marine Mammal Adaptations

  • Integument: The outer covering, such as the skin or fur of an animal
  • The mammalian integument is a complex, multi-layered structure.
  • Epidermis: Outermost layer, cells are often keratinized and provide water proofing.
  • Epidermal structures include hair, nails, claws, sebaceous (oil) and sweat glands
  • Dermis: Middle layer, formed by two regions of connective tissue
  • Papillary dermis has finger-like projections, each one carries blood vessels and verves toa position near the overlying epidermal cells.
  • Reticular dermis forms a connection with the underlying hypodermis
  • Hypodermis: Bottom layer, a more loosely woven connective tissue layer
  • Thermoregulation
  • Mammals are homeothermic endotherms with a high (36 to 38C) and stable body temperature.
  • Water conducts heat away from the body 25 times faster than air.
  • Adaptations to deal with this
  • Low Surface area to Volume ratio decreases the relative area across which heat is lost.
  • Marine mammals tend to be large, which means they have a small surface area to volume ratio, thus reducing heat loss.
  • Reducing thermal conductance, i.e. insulation
  • Fur:
  • Good in air, but loses most of its insulation when wet
  • Only the sea otter and fur seals have dense enough fur that the skin remains dry under water.
  • Sea otters also have a hydrophobic lipid, squalene, that helps keep fur waterproof.
  • Fat:
  • Marine mammals use “blubber”, a thick subcutaneous layer of fat for extra insulation
  • Blubber can be up to 30% of total body weight.
  • Not nearly as effective as dry fur, but better in the water.
  • Insulation depends on thickness and lipid content
  • Many marine mammals use both for insulation.
  • Marine mammals, may also face the problem of excess body heat, especially in tropical regions when they are swimming a lot.
  • Bypass insulation by transferring heat to areas of little insulation
  • Pinnipeds: the underside of the flippers.
  • Cetaceans: the fluke, dorsal fin, and flippers
  • Counter current heat exchanger
  • See Figure
  • Two sets of ‘pipes’ moving fluid between warm and cold areas can transfer heat very effectively.
  • These are the arteries and veins that run to and from the flippers, fluke and fin.
  • Drag Reduction
  • Because of the increased viscosity of water over air, life in the marine environment means more drag.
  • The energy used in order to move a body through a medium is directly proportional to its drag.
  • Therefore, reducing drag means that marine mammals save energy or swim faster.
  • Adaptations to reduce drag
  • Reduce hair, or the guard hairs are the leading hairs, they are flattened and thus for a smooth surface when wetted.
  • Streamlining reduces pressure drag
  • The hydrofoil shape is best at reducing pressure drag.
  • Buoyancy Control
  • When a body is submerged in water, it displaces a volume of water equivalent to its own volume.
  • If the weight of the body is less than or equal to the weight of the water it displaces, it experiences a net upward force and floats.
  • If the weight of the body is greater than the weight of the water it displaces it sinks.
  • Mammals are made of some stuff, bone and muscle, that are denser than water.
  • Other stuff, like air-filled lungs, body fluids, fats, oils and blubber are less dense than water
  • Two mechanisms to avoid sinking
  • Reduce the amount of muscle and bone
  • Increase the amount of air, body fluid, fat, oil and blubber.
  • Locomotion
  • Muscles pull on bones, which are attached at joints, thus creating leverage in order to pull water behind the animal and thus thrust it forward.
  • A lever system can be designed to optimize either its force output or the velocity at which it moves.
  • Fource output is increased by increasing
  • The force-in
  • The mechanical advantage of the lever system.
  • Example: California Sea Lion
  • Force-in is increased by the large muscles attached to the upper arm bone
  • Mechanical advantage is created by shortening the humerus
  • Propulsive efficiency is also increased by the shape of the ‘paddle’
  • Flukes in cetaceans
  • Hind flippers in phocids
  • Front flippers in Otariids
  • The hydrofoil shape of these structures creates thrust as well as lift and thus facilitates locomotion.
  • Skull Morphologies
  • In pinnipeds, otters and sirenians, the skull morphology is very similar to that of a terrestrial mammal
  • Cetacean skulls are different
  • Both odontocetes and mysticetes have a cranial elongation of the bones that form the rostrum (the snout) and a shortening of the braincase.
  • Mysticetes also have a tremendously elongated maxilla from which the long sheets of baleen hang.
  • The nostrils have migrated farther back on the head, which helps to breathe while in the water.
  • Sound production
  • Pinnipeds: Produce ‘normal’ barks and growls, like a dog, but also produce high frequency sounds, which may be used for echolocation. These other sounds are probably not produced in the larynx, but somewhere else.
  • Odontocetes: Produce high pitched sounds used for echolocation. Sounds are produced in the nasal plug and elaborate nasal sac system.
  • Nasal air sacs, steeply sloping maxillary bones and the rostrum reflect sounds and help focus sound through the melon, which focuses the sound.
  • Respiratory System
  • Many marine mammals are deep divers.
  • Pressure increases with depth such that every 10m is an additional atomosphere of pressure
  • At high pressures, nitrogen becomes solvent in body tissues. When it comes out of solution it can rupture the tissue, causing the bends.
  • How do marine mammals avoid this?
  • Oxygen is stored in the blood and muscles and air is kept out of areas that are in contact with blood.
  • For this reason many seals actually exhale before they dive.
  • Marine mammal lungs are reinforced so that they don’t collapse under the pressure and thus trap air where nitrogen could be absorbed into the blood.
  • Breathing in the water. How to keep from choking
  • Used to think the watery ‘blow’ of large whales was evidence that they inhaled seawater into their lungs. Not true.
  • How do deep diving animals keep water from entering their nostrils? How do they feed without breathing?
  • Nostrils close tightly
  • Pinnipeds: the neutral position is to have the nostrils closed, with a nasal plug sitting tightly against the bone.
  • Odontocetes: the larynx forms an elongated goosebeaklike structure that fits rigidly into the elongated nasal passage.Food passes around the larynx when swallowing and no food or fluids enter the respiratory system. The intranarial (within nose) position of the larynx effectively separates the respiratory tract from the digestive tract to a greater extent than that found in any other mammal.
  • Also allows odontocetes to simultaneously echolocate and swallow.
  • Feeding
  • Finding food
  • In addition to using sight, Pinnipeds and sea otters use their whiskers to feel for their food.
  • Odontocetes use echolocations, which works even in the dark.
  • Eating
  • Pinniped dentition is very similar to most carnivores
  • Some Peculiarities
  • Walruses- tusks grow to 80 cm in length
  • Crabeater seal feeds on krill (not crabs) and its teeth are shaped to create a sieve, similar to mysticetes.
  • Sirenians use lips and whiskers to gather food and lack incisors.
  • Constantly grind down their molars by chewing. Teeth migrate backward and are constantly being replaced.
  • Odontocetes feed on individual fish and squid.
  • Homodonts (all teeth the same) catch food and chew it.
  • Swallow by creating suction
  • Strapped-toothed whale has paired teeth that arise from the mandible and cross tightly above the dorsal surface of the rostrum, thus keeping the oral cavity from opening more than a few centimeters.
  • Mysticetes lack teeth and use baleen, plates of keratinized tissue that hang from their upper jaw.
  • Baleen plates grow continuously from the maxilla throughout the life of the individual. Each baleen plate is formed as a sandwich-two outer sheets of keratin surrounding a tubular-keratin “marrow’ layer. The action of the tongue passing back and forth across the baleen abrades the adjacent keratin sheets and exposes the tubular marrow layer
  • In the Bowhead whales, the baleen plates can grow to more than 4 m long, and number 300 per side
  • Blue whales ‘swallow’ 60m3 of water, by dropping their jaws 90 to the side, creating a suction. The tongue and pleat blubber contain large amounts of elastin fibers, which can be stretched to four times their resting length. As the oral cavity expands, the soft, flaccid tongue inverts and lines the floor of the oral cavity. The whale’s mouth is then closed by both the action of the jaw muscles and rotation of the animal. Contraction of muscles and elastic energy stored in the ventral groove blubber help shrink the oral cavity. Seawater is eject through the baleen, leaving the food behind.
  • Balaenids are skimmers, that is they swim slowly with their mouths open, straining small prey through their baleen filter.
  • Ex: The grey whale feeds predominantly by engulfing benthic sediments and filtering the associated fauna