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Diving Physiology of Marine Mammals Fundamental Challenge AIR / OXYGEN Separation of Critical Resources FOOD NUTRIENTS Marine Mammals Cetacea: odontocetes and mysticetes Pinnipedia: otariids, phocids and odobenids Sirenia: manatees and dugongs Carnivora: sea otters & polar bears Mysticeti Cetaceans Odontoceti Pinnipeds Otariids Odobenids Phocids Sirenians Manatee Dugong Carnivores Sea Otter Polar Bear Special Adaptations Anatomical and physiological adaptations in the respiratory & cardiovascular systems, blood, and peripheral tissues result in: ◦ Efficient ventilation ◦ Enhanced oxygen storage ◦ Regulated transport and delivery of respiratory gases ◦ Extreme hypoxic tolerance ◦ Pressure tolerance Diving Behavior Dive duration Dive depth Diving Behavior: Cetaceans SPERM WHALES: Routine dives : 400m for 40min Maximum depths: 2000m BEAKED WHALES: Routine dives: ◦ 800 m for 60 min Maximum durations: ◦ 120 min Diving Behavior: Cetaceans Bottlenose dolphin (Tursiops truncatus) typically dive <5 min & <20 m Large baleen whales typically dive <5 min; can reach depths of 200 m Diving Behavior: Pinnipeds Large phocid seals are the longest-duration divers among the pinnipeds Maximum depths range: 600m to 1500 m Diving Behavior: Pinnipeds Routine dive durations of most other phocid seals are less than 10 min. Diving Behavior: Pinnipeds OTARIIDS Routine dives: <3 to 4 min ODOBENIDS: Routine dives: <4 to 6 min Diving Behavior: Sirinians Typical dives: 2 to 3 min, 12 m at most Diving Behavior: Sea Otters Average Dives: 1 to 3 min, <30 m deep. Diving Fundamentals Dive Response: ◦ Apnea ◦ Bradycardia ◦ Peripheral Vasoconstriction Oxygen Stores: ◦ Lungs ◦ Blood ◦ Muscle Researching Diving Physiology Per Scholander (1905-1980)– observations of cartilaginous reinforcement of airways Hypothesis - more rigid airways would allow: ◦ Movement of air into those airways during compression of the lungs at depth ◦ Alveolar collapse ◦ Cessation of gas exchange, and, in particular, nitrogen absorption at depth Researching Diving Physiology Kooyman and colleagues documented the airway reinforcement of diving mammals in comparison to terrestrial mammals. Most prominent in cetaceans and sea lions ◦ Cartilaginous reinforcement: trachea to alveoli Less so in walruses and sea otters ◦ Distal airways reinforced by a mix of cartilage and muscular elements Respiratory Mechanics Reinforcement of the distal airways in diving mammals allows for the movement of air from the alveoli into the bronchi during lung compression Promotes collapse of the alveoli and cessation of gas exchange at depth. Respiratory Mechanics Maximum expiratory flow rates: ◦ 162 liters s−1 in bottlenose dolphins ◦ 202 liters s−1 in young gray whales Necessary in cetaceans since exhalation and inhalation occur in less than 1s Such flows allow for a tidal volume as high as 88% of TLC in the pilot whale. Respiratory Mechanics High flow rates minimize the time for exhalation/inhalation cycle Rapid breaths allow animals to spend most of their travel time below the surface where drag is less Lung Volumes Lung volumes of diving mammals are in the general range of terrestrial mammals. Notable exceptions: ◦ small lungs of the deep-diving bottlenose whale ◦ large lungs of the shallow-diving sea otter. Diving Lung Volumes Diving lung volumes: ◦ lung volume at the start of a dive ◦ important determinants of the size of the respiratory O2 store during a dive. Many cetaceans appear to dive on inspiration, while pinnipeds usually dive on expiration. Consequently, the diving lung volumes of cetaceans are probably near TLC, while pinnipeds are closer to 40-50% TLC Oxygen Transport - Hb Marine mammals have exceptionally high [Hb] values compared to terrestrial mammals. O2 affinity of Hb not that different from terrestrial counterparts The P50, the O2 partial pressure at 50% Hb saturation, is in the range of 26 to 30 mmHg Hb is most elevated in long-duration divers. Oxygen Transport - Mb [Mb] in diving mammals are 10 to 30 times that found in terrestrial mammals. High [Mb] have long been considered to serve as an O2 store during diving. High [Mb] also facilitate O2 diffusion Calculating O2 Stores ◦ Lung ◦ Blood ◦ Muscle TOTAL OXYGEN STORES Total Body O2 Stores Total body O2 stores of diving mammals on a mass-specific basis range from two to five times that of human O2 stores Also notable is the change in the distribution of O2 stores among species. Distribution of Body O2 Stores Species mL O2 kg-1 Lung % Blood % Muscle % Human 20 24 57 15 Odontocetes 35 22 30 48 Otariids 40 13 54 33 Phocids 60 7 65 28 Sea Otter 55 55 29 16 Manatee 21 33 60 7 Circulatory Responses Cardiovascular regulation is critical during diving of all marine mammal species. Changes in heart rate and cardiac output contribute to: (1) the rate of O2 uptake from the lungs (2) the magnitude of O2 delivery and consumption in tissues Diving Heart Rate The physiological hallmark of diving is a decrease in heart rate during dives. Bradycardia Extreme example: 7 bpm average heart rate of a gray seal during a 14 min dive Circulatory Responses Bradycardia ( HR) Peripheral Vasoconstriction: blood flow and blood O2 conserved for the heart and brain, directed away from peripheral tissues and other organs HR and perfusion control the rate of depletion of the blood and lung O2 stores. Diving Heart Rate Increase in heart rate during ascent = anticipatory tachycardia Allows increased muscle blood flow and O2 extraction blood O2 is depleted by the end of the dive and increases Po2 gradient Maximizes respiratory gas exchange, and minimizes duration of surface interval. Aerobic Dive Limit Oxygen stores and oxygen utilization dictate the amount of time an animal can spend underwater Aerobic Dive Limit Defined by Kooyman (1983) as the amount of time an animal may spend diving before an increase in blood lactate levels occurs. Determining factor in the amount of time an animal is capable of foraging underwater. Blood cADL= total body oxygen stores oxygen demand Muscle Lung Ecological Implications Consequences for Immature Animals What does all of this mean for immature marine animals? Increased Metabolic Rates Limited Oxygen Stores Increased Metabolic Demand Northern Elephant Seal (Mirounga angustirostris) Harbor Seal (Phoca vitulina) Burns et al. 2005 Rea & Costa 1992 Thorson & LeBoeuf 1994 Weddell Seal (Leptonychotes weddellii) California Sea Lion (Zalophus californianus) Liwanag et al. 2009 Ponganis et al. 1993 Limited Oxygen Stores Emperor Penguins (Aptenodytes forsteri) Blood Oxygen Stores: 6 mo = At/Near Adult Levels Muscle Oxygen Stores: 6 mo = 31% adult values Ponganis et al. 1999 Limited Oxygen Stores Bottlenose Dolphins (Tursiops truncatus) Total Body Oxygen Stores = >3 Years Noren et al. 2002 Ecological Implications cADL = TOTAL OXYGEN STORES OXYGEN DEMANDS 9 min 19.1 min Ponganis et al. 1993 Ecological Implications http://www.youtube.com/watch?v=vJvfjiCTvq4
