22 



THE BIOLOGY OF MARINE ANIMALS 



common among crustaceans, cephalopods and fishes of the dimly lighted 

 mesopelagic region. Complex photophores are characteristic of animals 

 in this region, but many light-producing organisms are also found at 

 greater depths, either in abyssal pelagic waters or on the bottom (3 1 , 39, 40). 

 Pressure. Pressure alterations with depth form a major environmental 

 variable in the bionomics of marine animals. Pressure increases by about 



OS 1 5 10 50 



Percentage of Sub-surfa.ee Illumination 



WO 



Fig. 1.8. Penetration of Daylight into Coastal Water (English Channel) 



The graphs refer to spectral ranges as follows: red 700+ ; red 600+ ; ultra-violet, 

 330-420; yellow, 550-80; blue, 330-480; blue-green, 455-80; green, 480-580 m//. 

 (After Atkins (2).) 



1 atmosphere for each 10 metres increase in depth, and shows a range from 

 zero at the surface to some 1 ,000 atmospheres in the ocean deeps. 



Great pressures such as occur in the ocean depths are known to have 

 profound effects on certain physiological and biochemical processes, but 

 relatively little is known about how they influence marine animals. It has 

 long been recognized that life exists in the abyssal regions, and the organ- 

 isms occurring there are certainly physiologically adjusted to the great 

 pressures which they encounter. Specimens have been obtained from the 

 Philippine trench at over 10,400 metres, namely actinians, lamellibranchs, 

 holothurians and echinoids, all of which were dead on reaching the 

 surface (7). 



