INTRODUCTORY 9 



included young stages offish and cephalopods. The temporary members of 

 the plankton attain great abundance during the spring and summer, only 

 to disappear after metamorphosing, settling on the bottom or perishing. 

 In addition there are certain temporary planktonic forms which are 

 characteristic of the open ocean, such as the Phyllosoma larva of the rock 

 lobster Scyllarus, and the Leptocephalus larva of the eel. 



CHEMICAL AND PHYSICAL PROPERTIES OF SEA WATER 



Physical and chemical conditions in the oceans have been investigated 

 actively since the voyage of the Challenger in 1872-6, and extensive data 

 are at hand for forming an appreciation of sea water as an environmental 

 medium for animal life. The environmental variables which are of immedi- 

 ate interest to the biologist are temperature, density, viscosity, pressure, 

 light, salinity, suspended matter and dissolved gases. These are briefly 

 reviewed in the following pages and are related, in so far as is practicable, 

 to their biological effects. 



Chemical Composition of Sea Water 



Sea water contains a characteristic assemblage of dissolved solids and 

 gases, and a variable amount of suspended inorganic and organic material. 

 As first shown by Dittmar on the Challenger expedition samples, the main 

 constituents of sea water, with minor exceptions, show remarkable uni- 

 formity throughout the oceans of the world. This fact is of fundamental 



TABLE 1.1 

 Average Composition of Sea Water (Chlorinity 19°/ 00 , Salinity 34-325°/ 00 ) 



* Bicarbonate and carbonate will vary according to the pH of the sea water. 



importance in oceanography and marine biology, since it ensures that the 

 results of studies on the physical properties of sea water in any part of the 

 world are of general and universal significance. Table 1.1 shows mean 

 values for the principal dissolved substances in sea water of chlorinity 

 19% 1 (salinity 34-325% ). 



1 See p. 10 for explanation of °U 



m.a. — 1 



