172 



THE BIOLOGY OF MARINE ANIMALS 



Whales can dive deeply, and there is evidence that some species regularly 

 go down to great depths. Harpooned right and fin whales are reported as 

 descending to 500-1,200 metres, and there is a record for the sperm whale 

 of 1,600 metres. How do they tolerate these pressures and escape caisson 

 disease? The lungs of whales are not unusually large in proportion to their 

 size and may not be fully inflated during a dive. The whale takes down only 

 a limited supply of air (including N 2 ), which is not replenished as in 

 human diving apparatuses. Moreover when the whale makes a deep dive 



3 mm periods 



J I I L. 



-I I I I 1 I I [ I 



^•*ttlH#i||j^r 



mg% 



Lactic 



Acid 



Dive 

 15 mm 





Arterial Blood 



Respiration 



Fig. 4.15. Changes in the Arterial Blood of the Grey Seal Halichoerus 



grypus During a Dive under Experimental Conditions. 



(From Scholander (140).) 



its lungs are compressed and reduced in volume, air is displaced into 

 bronchial and tracheal dead space, and the alveolar surface becomes re- 

 duced and thickened, all of which are factors reducing or slowing diffusion 

 of nitrogen into the blood. In addition much of the peripheral circulation 

 is closed off. It is probable then that the limited amount of N 2 available 

 is insufficient to supersaturate the blood seriously, and the limited blood 

 volume exposed to nitrogen at high pressure is diluted with blood from the 

 periphery when the animal surfaces (100, 140). 



RESPIRATORY PIGMENTS 



The oxygen capacity of water is low (sea water 0-54 vol% at 20°C), and 

 is inadequate as an oxygen carrier except for animals having low meta- 

 bolism. Many animals which possess circulatory systems have blood 

 pigments which serve to increase greatly the oxygen-carrying capacity of 

 the blood or haemolymph. Blood pigments are compounds which combine 

 loosely with oxygen. They belong to several different chemical categories 

 but they have this in common that they contain some metal, usually iron 

 or copper, in combination with protein. In the following section we shall 

 examine their role in oxygen transport among marine invertebrates and 



