THE LAW OF THE MINIMUM IN THE 



SEA 



By JAMES JOHNSTONE, B.Sc. 



Fisheries Laboratory, University of Liverpool 



Two methods of research developed during the last twenty 

 years by the German and Scandinavian marine biologists are 

 now affording results of very great interest. One of these lines 

 of research is the investigation of the relations between the 

 nature and abundance of the floating microscopic life of the 

 sea, the plankton, and the physical changes that take place in 

 the water from time to time; and the other is the quantitative 

 investigation of the fauna and flora of the sea. The validity 

 of both of these methods of investigation is still, to some 

 extent, a matter of controversy — that is to say, some marine 

 biologists doubt whether we can associate together, with any 

 degree of certainty, the physical changes that take place in 

 the sea with the nature of the plankton ; while others argue 

 that, because of the apparently fortuitous distribution of life 

 in the sea, it is impracticable to attempt any estimate of the 

 absolute abundance of organisms in the open water, or on 

 the sea bottom. Certainly neither of the two methods to 

 which I have referred is yet thoroughly developed, and cer- 

 tainly both will be greatly improved. But, nevertheless, each 

 has produced results which have enormously stimulated 

 investigation in other directions. 



P. T. Cleve, of Upsala, and Otto Pettersson, of Stockholm, 

 were the first to attempt to correlate the composition of the 

 plankton with the physical condition of the sea. It had long- 

 been known that the waters of the seas of Northern Europe 

 were derived in the main from two sources — the Equatorial 

 current circulation of the tropical Atlantic and the southerly 

 flowing Arctic streams. Cleve l described a number of 

 11 plankton-types " which were characteristic of these main 



1 Treatise on the Phytoplankton of the Atlantic and its Tributaries, Upsala, 1897. 



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