Introduction to the Biology of Marine Life by John Morrissey & James Sumich

Author:John Morrissey & James Sumich
Language: eng
Format: mobi, epub
Tags: Science, Life Sciences, Marine Biology
ISBN: 9780763781606
Publisher: Jones & Bartlett Learning
Published: 2010-12-28T14:00:00+00:00

SUMMARY POINTS

Diving Tetrapods

The physiological basis for the deep and prolonged breath-holding dives by marine birds and mammals, which vary considerably, are poorly defined.

Larger species of whales, and diving penguins and pinnipeds, commonly follow dives of several minutes by several blows 20 to 30 seconds apart before another prolonged dive is attempted in an apneustic breathing pattern. Apneustic breathing provides time for the lungs to extract additional O2 from the air held in the lungs.

The lungs and rib cage of cetaceans and pinnipeds smoothly collapse as the water pressure increases during deep dives. Complete lung collapse probably occurs in the upper 100 m. By tolerating complete lung collapse during dives, these animals sidestep the need for respiratory structures capable of resisting the extreme water pressures experienced during deep dives, and they avoid the barotrauma sometimes experienced by humans after prolonged breathing of air under pressure.

The combination of bradycardia, peripheral vasoconstriction, and other circulatory adjustments to diving has been commonly referred to as “the mammalian diving reflex.” Studies of free-diving Weddell seals in Antarctic waters support a substantially different picture of diving responses in unrestrained seals in their natural habitat. Weddell seals anticipate dive duration and then consciously make the appropriate circulatory adjustments before leaving the surface.

Elephant seals spend months at sea foraging at depths between 300 and 1500 m. Their feeding dives are typically 20–25 min long, night and day for weeks on end, with only 2–4 min spent at the surface between dives.

Deep-diving whales are not accessible to researchers in the way some seals are, yet they likely surpass seals in both maximum depth and duration of dives due to their more derived anatomy and physiology. Future advances in telemetric methods for recording data from free-swimming cetaceans during voluntary dives will likely provide extremely interesting information.

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