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Nekton Chapter 3

Nekton Chapter 3. Questions to investigate…. How do nekton control buoyancy, and why is this important? What are some adaptations in nekton to rapid and efficient locomotion? How do nektonic organisms defend or camouflage themselves against predators?

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Nekton Chapter 3

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  1. NektonChapter 3

  2. Questions to investigate… • How do nekton control buoyancy, and why is this important? • What are some adaptations in nekton to rapid and efficient locomotion? • How do nektonic organisms defend or camouflage themselves against predators? • What kinds of sensory systems do nekton have? • What types of migrations do nekton undergo, and for what purpose? • How do marine mammals dive, from a physiological standpoint? What challenges must be overcome, and how do they accomplish this?

  3. Buoyancy adaptations

  4. countershading counterillumination Camouflage

  5. The lateral line • Sensory pits that sense pressure changes in the water

  6. Ampullae of Lorenzini on Gray Reef shark snout Ampullae of Lorenzini • Sharks and rays have these • Sensory pits that pick up electric currents; very sensitive • Used to find prey

  7. Migrations • Primarily marine mammals, sea turtles, some fish • Anadromous: live in seawater, migrate to freshwater to spawn • e.g. salmon • Catadromous: live in freshwater, migrate to seawater to spawn • e.g. European & American eels • Why migrate???

  8. Whale migrations

  9. Whale migrations

  10. Types of caudal fins A: heterocercal B: rounded    C: truncate    D: emarginate    E: lunate    F: forked G: pointed (confluent with dorsal & anal fins)    H: pointed (separated from dorsal & anal fins)

  11. Caudal fin aspect ratios(and their function) • Aspect ratio (A) = (fin height)2 / fin area • Low A: rounded, heterocercal tails • High A: truncate, forked, lunate tails Caudal fin types and functions Rounded: A = 1; for angling, maneuvering Lunate: A = 7-10; reduced drag at high speeds Heterocercal: A = 2; lift from asymmetry

  12. Marine mammals • Pinnipeds – walrus, seals, sea lions • Cetaceans – whales, dolphins, porpoises Click here to see examples of traits (dolphins vs. porpoises)

  13. Cetacean family tree Heyning, John E. Masters of the Ocean Realm: Whales, Dolphins, and Porpoises. (Seattle: University of Washington Press, 1995), p. 29. (from www.nhm.org)

  14. Cetaceansbaleen whales (mysticetes) • Species include the:right, pygmy right, gray and rorqual (humpback, fin, Bryde's, blue, northern minke, Antarctic minke, Eden's, and sei whales) whales • Baleen whales have 2 blowholes What and how do baleen whales eat?

  15. Cetaceanstoothed whales (odontocetes) • Species include the: sperm whales, pygmy sperm whales, beaked whales, river-dolphins, belugas and narwhals, dolphins and porpoises • Toothed whales have only 1 blowhole What and how do toothed whales eat?

  16. Heat retention in marine mammals • Low surface area : volume ratio (big body) • Thick layer of insulating blubber • Countercurrent blood flow in extremities (areas most likely to lose heat)

  17. Diving in marine mammals • Marine mammals don’t get the “bends”(N in bloodstream comes out of solution when the diver ascends quickly. Gas bubbles can lodge in joints, brain, lungs and can be painful to deadly) • Air is taken in at surface, not under pressure • Lungs collapse at depth, under pressure, preventing gas from entering bloodstream • Few ribs attached to a shortened sternum allows flexibility in the rib cage under pressure

  18. Diving in marine mammals • Collapse of lungs lowers buoyancy, allows organism to sink faster when diving • Larger blood volume = more O2 can be carried in the bloodstream • Blood holds more O2 per unit volume (more hemoglobin) • Bradycardia – slowing of heartbeat • Blood supply cut off to non-essential organs & organ systems (blood shunted to brain, CNS, heart)

  19. Diving in marine mammals • Muscles have myoglobin that stores more O2 than hemoglobin • Muscles can function anaerobically when O2 is used up • Apneustic breathing at surface – rapid breaths, quickly fill lungs, replenish O2 in blood, muscles • Highly efficient O2 extraction by alveoli

  20. Diving in cetaceans:differences among species • Click here for a web site showing diving times and depths by cetacean species

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