1 8 College of Forestry 



zoologist, Dr. C. G. Joh. Petersen, to devise apparatus and 

 methods for a census of the Hfe of the sea bottom by means 

 of the examination of many samples of a unit area (see 

 Bibliography). For these studies Petersen invented a bottom 

 sampler which brought up a sample of the sea bottom one- 

 tenth of a meter square, the layers of bottom soil being in their 

 natural position. A series of these unit areas, when examined 

 for the animal and vegetal life, gave a fairly accurate picture 

 of the bottom of the sea, and this method enables the student 

 to secvn^e with this sampler a reasonably accurate census of 

 the animal population of large areas of the bottom of both 

 seas and inland waters. 



Previous to Petersen's investigations the quantitative studies 

 were chiefly confined to the plankton organisms, which were 

 designated the " pastures of the sea " and which were be- 

 lieved to afford the greatest and most important food supply 

 for fish and other marine animals. Petersen has shown, with 

 the aid of the centrifuge, that the water is also filled with very 

 fine particles of organic matter, called by him dust-fine- 

 detritus, which far exceeds the plankton in amount and is 

 thought to be of greater value as a source of food. In fact, 

 the detritus should be included with the animals and plants 

 usually recognized as forming the plankton, which should 

 include any and all organic matter, alive or dead, that floats 

 or is carried about in the water by means of currents. Peter- 

 sen's methods of quantitative work places a new value on such 

 investigations and should stimulate research in the direction 

 of a census of our aquatic population, both marine and fresh- 

 water. Such studies are statistical and are based on the 

 examination of many associational units. It is realized that 

 the conditions of life in the sea are not exactly comparable with 

 those of our inland lakes and streams, but the same general 

 methods may be used, modified to meet local conditions, and 

 the same kind of generalizations may be reached. 



Recently, another European biologist, Sven Ekman ('15), 

 evidently inspired by Petersen's work and methods, made an 

 ecological, quantitative, and qualitative study of Lake Vatter, 

 situated about 115 miles southwest of Stockholm, Sweden. A 



