EVOLUTIONARY ADAPTATION TO SEAQUAKES
by Captain David Williams
Deafwhale Society, Inc
PO Box 319, Dumaguete City
6200 Oriental Negros
Philippines
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Hundreds of years ago with the oceans were teaming with food, a seaquake-injured pod would have plenty of opportunity to catch something to eat on the surface while they waited to heal and begin diving again. Injured pods might have been carried out of an area before their injuries healed. If so, then seaquakes might have presented an evolutionary advantage in that it thinned pods from one particular area and caused them to move downstream to repopulate a new area. This would have spread the species around the ocean and prevented over-grazing on one particular range.
For certain, whales and earthquake-induced pressure waves have coexisted for 50 million years; much of this time the oceans were 10 to 20 fold more active seismically (click here to read more about evolution of whales). These animals must have made evolutionary changes throughout their vascular system validating the hazard of pressure waves generated when the seafloor dances up and down during certain submarine earthquakes, yet not one single scientific document exist that makes even a simple mentioned of this fact.
Since marine mammal scientists have ignored seaquakes, its not hard to understand why the anatomists, who meticulously detailed the internal workings of whales, were not concerned with this potential danger. Naturally, if the idea never occurred to them that whales faced such a hazard, one would not find specific reference to seaquake adaptation in the material they published. Rather, one would expect the adaptations made to living in a seaquake prone environment would be assigned secondary and/or enigmatic functions.
Professor Matthews (1978) makes note of a peculiar arrangement of blood vessels in many mammals that is particularly elaborate in whales. This takes the form of networks of blood vessels communicating with each other, massed together to form complicated tangles of some size, the retia mirabilia. These vessels take various forms such as arteries communicating with veins, arteries communicating with each other, and other varieties. In land animals, these vessels usually occur related to the joints of the limbs, or at the base of the brain, but in whales they are much more widespread, and are particularly conspicuous as arterial retia on the inside wall of the chest and between the ribs.
Matthews states: "The function of the retia is not properly understood, though as they are so conspicuous and massive in the cetaceans they are presumably in some way connected with diving. It has been suggested that they act as reservoirs of oxygenated blood, but the total amount of blood they hold is not enough to be useful in a long dive. It may be that they regulate the flow of blood through the brain, those in the skull ensuring that it is supplied with oxygen when the other parts of the body are deprived, or it could be that they are concerned with counteracting any adverse effects of increased pressure at depth, though as the pressure is bound to be equal throughout the tissues of the body it is not clear what adverse effects may be produced.”
What would Matthews have written had he been aware of pressure waves from seaquakes?
Professor Slijper (1958) in his book on whales stated: "…the retia are capable of absorbing and releasing vast quantities of blood. This is particularly true of the arterial retia, and though the structure of the venous retia has not yet been studied sufficiently, we can nevertheless state that they to can store blood for some time, as can the special hepatic veins and the inferior vena cava. The spinal veins, moreover, may enable blood from the brain to return both to the thorax and to the abdomen so that, if the flow to the thorax is impeded for some reason, congestion in the delicate central nervous system is avoided. Furthermore, blood from the abdomen can, under certain conditions, be diverted to the thorax through the spinal canal instead of the inferior vena cava which normally carries blood. All these modifications are obviously associated with possible pressure differences between the thorax and the abdomen, and possibly between both and the brain."
Professor Slijper also indicates that great quantities of elastic fibers are found throughout the tissue of the lungs, the walls of the bronchi, and the pleura, where they are much more plentiful than in terrestrial animals, and suggested that by increasing the flexibility of the lungs, great pressure changes can be more easily handled.
Are these evolutionary changes forced by seaquakes?
Naturally, pressure differences would arise between the head and tail of a whale twenty meters long in the vertical position, and these networks would help balance blood flow to parts of the anatomy at dissimilar ambient pressures. But is such a network necessary? Working muscles would alter blood pressure inside vessel walls, assisting flow throughout.
On the contrary, if a seaquake occurred while the whale was in a vertical position, such vascular networks would be crucial. Seismic pressure changes in the water column would crisscross the body of the whale, altering pressure throughout their anatomy regardless of position.
And, why have arteries communicating with veins?
Those who have examined stranded or harpooned marine mammals for the last 100 years have known of the uniqueness of their complex vascular system in absorbing and equalizing rapid pressure changes. The distinctive nature and toughness of their lungs, and the pressure regulating complexity of the massive air sinuses in their heads has all been attested to numerous times.
These diving mammals deal with rapid pressure changes many times every day as they dive to feed and interact with each other. By the very nature of form following function, any pressure regulating anatomical adaptation to diving in the ocean would be vulnerable to overpressure from excessively rapid and/or potent changes in ambient water pressure generated by undersea earthquakes. Maybe a new awareness of seaquake activity might spring forth and cause scientists to alter their view somewhat when it comes to the function of the complex vascular system in deep diving whales.
References:
Harrison, R.J., J.E. King, (1965) Marine Mammals, Hutchinson & Co LTD, London
Matthews, L.H. (1978) The Natural History of the Whale, Weidenfeld and Nicolson, London
Slijper, E.J. (1979) Whales, Cornell University Press