Field. — Sources of MaHne Food 187 



does contain a certain amount of proteins digestible by 

 pancreatin. In the upper layer from 44 to 68 milligrams 

 of digestible proteins per 100 square centimeters are 

 found, which means that the amount of digestible pro- 

 teins per square meter is approximately 5 grams. 



On the other hand digestible non-nitrogenous com- 

 pounds in the sea bottom consist of a fairly considerable 

 amount of material in the form of pentosans amounting 

 to from 0.3 to 1.0%. This is an important fact for there 

 is reason to suppose that the bottom fauna is able to 

 digest pentosan. It has been well established that her- 

 bivorous animals utilize pentosan as a food and Bieder- 

 man and Moritz (1898) showed that Gastropods were 

 able to digest pentosan. It is probable, therefore, that 

 bivalves also can digest pentosan and that the consid- 

 erable amount of pentosan present in the sea bottom 

 besides other possible substances (hemicellulose gen- 

 erally) plays an important part as non-nitrogenous 

 nourishment for a great portion of the bottom fauna. 



In support of Jensen's observations Blevgad, 1914, has 

 made an interesting study of the food of the commonest 

 and most widely distributed bottom-inhabiting animals 

 in the various communities of the Danish waters. His 

 report is based on the analysis of stomach contents. 

 Three main sources of nourishment for the bottom 

 fauna of the sea were determined. (1) Plants — fresh 

 growing plants of the benthos formation, chiefly eel 

 grass which in the Danish waters produces about 8,232,- 

 000 kilograms annually. In course of time, this decays 

 and falls to pieces forming (2) detritus. This includes 

 dead or dying organisms or portions of them whether 

 vegetable or animal in origin as are found in suspension 

 (or solution in the sea water) or deposited on the bottom. 

 Most of this detritus is of eel gras origin. (3) Animal 

 or carneous food or the third source includes all living 

 animals found in the sea, together with their carrion, 

 save where these are to be reckoned as forming part 

 of the detritus as just defined. 



