Field. — Sources of Marine Food 183 



of dry organic matter exclusive of the phytoplankton 

 consumed by the surface fauna. The total production 

 of phytoplankton he estimated to be 150 grams per 

 square meter annually. Jensen by very careful calcula- 

 tions estimates that in the Danish waters about 100 

 grams of organic dry matter per square meter is pro- 

 duced each year by the phytoplankton. For eel grass 

 the percentage of dry organic matter produced annually 

 per square meter he found to be 1,920, 1,120 and 344 

 grams in good, moderate, and bad localities respectively. 

 Eel grass beds cover about one-seventh of the area 

 studied (between the Skaw and the Baltic) which means 

 that the annual production of eel grass per square meter 

 of the water as a whole is 120 grams of organic matter. 

 Comparing the production of eel grass and plankton on 

 a basis of Jensen's calculations we see that eel grass 

 produces 120 grams of organic matter per square meter 

 while the plankton produces 100 grams. 



Now the question arises, how much of the organic 

 matter from each source is deposited on the sea bottom? 

 Undoubtedly much of the matter of the plankton dis- 

 solves following the death of the organisms due to the 

 action of baceria. Admitting that a portion of the eel 

 grass material is similiarly lost it is evident that the 

 plankton organisms with their relatively far greater 

 surface are in a much higher degree liable to destruction 

 than the eel grass. Furthermore a large part of the 

 plankton is devoured by the plankton fauna which would 

 lead one to believe that but a limited portion of plankton 

 production is deposited on the sea bottom. These cal- 

 culations are supported by the results of chemical 

 analyses of the organic matter in the sea bottom. Jensen 

 has done this and states his conclusions as follows : "In 

 the more sheltered waters the organic matter of the sea 

 bottom is derived almost exclusively from the Zostera 

 (eel grass) ; in the more open waters, it is possible that 

 the plankton organisms may play a not altogether unim- 

 portant part as a source of the organic matter of the 

 bottom." 



