Marine Mammal Physiology • Constraints of a Marine Existence o Breath-Holding (Apnea) for Diving § Marine Mammals are good divers • Sperm whale can stay under for >2hrs diving 1000-2000m • Hooded seals exceed 1000m, staying under for >50min § Asphyxia: The combined effects of lack of oxygen (hypoxia), increased carbon dioxide, and the accumulation of the products of anaerobic metabolism, such as lactic acid and hydrogen ions § Aerobic metabolism sustains the brief dives as well as the first parts of the deeper dives, but in longer dives it switches to anaerobic metabolism. § Adaptations • Oxygen storage o Relative to body size, marine mammal lung capacities are not much greater than terrestrial mammals. o Oxygen storage is increased in the blood and muscles and they have more blood than terrestrial mammals. o The oxygen storage potential in blood and tissue is correlated with the diving abilities of the animal. • Diving Bradycardia (Decreased Heart Rate) o Low heart rates (5% of predive rate) have been recorded in phocids o Dolphins can reduce their heart rates from 100 to 12 beats/min. • Preferential distribution of oxygen to various body tissues during apnea. o Mammalian Diving Response: Regional vasoconstrictuion within those organs that tolerate a prolonged lack of oxygen. This selective ischemia (when tissues are deprived of circulating blood) lowers the metabolism of those tissues are reduces asphyxia. o Blood is drawn from areas of less importance to areas of greater importance. o Sufficient blood pressure is maintained for perfusion of the vital organs, brain and heart. o Pressure § Pressure increases by 1 atmosphere for every 10m of depth • Therefore, the weddell and elephant seals regularly experience 50 to 100 atmospheres of pressure. § Barotrauma-damage caused by rapid expansion or squeezing of gas spaces that exceeds the structural integrity of tissues.• Lung Squeeze- when the tissues deform to the point of stress. Limits human breathing dives to about 30m. • Deep diving marine mammals have flexible chest walls and other structures capable of sufficient collapse to render the lungs airless. (See May 13 Notes) o This keeps air from coming in contact with tissues at high pressures and thus removes the possibility of the “Bends”, Nitrogen Narcosis, Oxygen Toxicity and Hypoxia. o Temperature Regulation § Marine mammals are endotherms, meaning they maintain and high and constant internal body temperature, which allows metabolic reactions to occur consistently. § Adaptations • Metabolic heat production: o Increase the amount of heat produced from food. • Insulation o Blubber and fur (See May 13 Notes) • Lower Respiratory Heat Loss o Seals use counter current heat exchange to cool air leaving their lungs and retaining heat in their bodies. o Water and Salt Balance § Osmosis: The movement of water and salt across a permeable membrane due to a differential in concentration across that membrane. • If you have a body of high salt concentration (and therefore low water concentration) sitting in an environment of lower salt concentrations (and therefore high water concentration), water will flow into the body and salt will flow into the environment. • The reverse also occurs. • Can result in dessication (losing too much water), or plasmolysis (the rupturing of cells that get filled with water). § Marine mammals maintain a body salt content comparable to that of terrestrial mammals, even though they live in a salty environment. • Osmolality (osmotic potential) of sea water is about 1000 mOsm/kg. For humans, it’s about 290 to 300 mOsm/kg and for seals it is about 330mOsm/kg • In order make up the difference marine mammals remove excess salts in very salty uring (2000 to 4000 mOsm/kg) • Kidneys o Primary site of water conservation as well as electrolytes and other substances necessary for lifeo Marine mammals have very large kidneys, that receives a lot of metabolic energy. • Seawater drinking o Marine mammals take in a lot of seawater in what they eat. § One study found California seal lions could maintain water balance solely by the food intake of fish, without access to freshwater. § Pups have been seen drinking freshwater and even snow. • Special Cases o Sirenians live in brackish (fresh/salt) water and can consume either fresh or saltwater without problems. o Some seals use a countercurrent flow of respiratory gases to conserve water. Cooling of expired air causes condensation of