Presstire Increase with Depth 29 



not survive long under the conditions of the low temperature and 

 lack of food. 



Pressure Increase with Depth 



If the relatively slight reduction in pressure with altitude in air is 

 important to some organisms, the tremendously greater increase in 

 pressure with depth in water might be expected to have serious con- 

 sequences to all aquatic organisms. When early calculations were 

 made of the magnitude of the pressure at the bottom of deep lakes, 

 and particularly of the ocean, it was believed that the stupendous 

 pressures would annihilate all living beings, so that the greatest depths 

 in the aquatic environment must be lifeless. This conclusion seemed 

 at first to be confirmed by the early explorations, but, with the im- 

 provement of gear for investigating the bottom of the deep sea, animal 

 life was gradually discovered at greater and greater depths in all the 

 ocean basins (Fig. 3.5). In 1951 the Danish Galatlwa Expedition 

 trawled 17 sea anemones, 61 sea cucumbers, 2 bivalves, and 1 

 crustacean from a depth of about 10,500 m off the Philippine Islands. 

 At this depth the pressure is 1050 atmospheres, or about 1 ton on each 

 square centimeter, but this terrific weight of water does not crush the 

 organisms living at that depth because the pressure is the same inside 

 their bodies as outside. 



When most deep-sea animals are brought to the surface, they are 

 dead or dying. The popular opinion is that they have been killed 

 by a violent release of pressure. In reporting the work of the re- 

 search vessel Atlantis, a newspaper once stated: "The sudden change 

 of pressure when deep-sea fish are brought to a higher level in the 

 ocean causes them to explode. The fragments are then put together 

 again!" Fish with air cavities within their bodies do indeed expand 

 when they are brought to a higher level, but most fish inhabiting the 

 ocean abyss have no air bladders. Their death is due primarily to 

 injury from the nets and to the change in temperature experienced in 

 being brought to the surface. 



The effect of the pressure changes in the aquatic environment is 

 very different for organisms with and without air cavities. Aquatic 

 plants that live at levels considerably below the surface stratum and 

 the great majority of deep-sea animals do not have gas-filled spaces 

 in their bodies. Since any cavities in these organisms are completely 

 filled with fluids, no mechanical deformation is caused by pressure 

 changes because the watery tissues are only slightly compressible. 



