SEA MUSSEL MYTILUS EDULIS. 211 



Calculations on the production of phytoplankton and eelgrass per square meter of 

 surface have been attempted, but what has been done so far approaches a mere approxi- 

 mation only. In regard to the phytoplankton, Hensen (1887) figured that 1 square 

 meter of surface produces annually 15 to 18 grams of dry organic matter exclusive of 

 the phytoplankton consumed by the surface fauna. The total annual production of 

 phytoplankton he estimated to be 1 50 grams per 1 square meter. Jensen, by very care- 

 ful calculations, estimated that in the Danish waters about 100 grams of organic matter 

 per square meter are produced each year by the phytoplankton. For eelgrass 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. Eelgrass 

 beds cover about one-seventh of the area studied (between the Skaw at the most 

 northern tip of Denmark and the Baltic Sea), which means that the annual production 

 of eelgrass per square meter of the water as a whole is 120 grams of organic matter. 

 Comparing the production of eelgrass and plankton on a basis of Jensen's calculations 

 we see that eelgrass 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 de- 

 posited 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 bacteria. Admitting 

 that a portion of the eelgrass material is similarly 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 eelgrass. 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 calculations 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 (eelgrass); in the more open waters it is possible that the plankton organisms may play 

 a not altogether important part as a source of the organic matter of the bottom. 



The transformation of nitrogen during the decomposition of eelgrass and its re- 

 lation to the nitrogen content of the organic matter in the sea bottom was also inves- 

 tigated by Jensen. He found that the green eelgrass is as rich in nitrogen as peas or 

 beans, which contain about 3 per cent. As the eelgrass decomposes the percentage of 

 nitrogen decreases until it is as low as 0.88 per cent, then as decomposition continues 

 it rises again up to 1.39 per cent. Analyses of the organic matter in the sea bottom in- 

 dicate that the average amount of nitrogen present is 4 per cent. Thus it is evident 

 that the organic substances of the sea bottom contain a greater proportion of nitrogen 

 than the eelgrass. 



Why the organic matter in the sea bottom is so much richer in nitrogen than the 

 eelgrass, from which it is formed chiefly, is readily explained by Jensen. As has been 

 shown the amount of nitrogen in the green eelgrass is greater than that in the early 

 stages of decomposition. Later the amount of nitrogen increases, becoming much 

 greater than in the green eelgrass. The diminution in nitrogen during the first stages 

 may be due to the fact that a portion of the nitrogenous protoplasm is dissolved in the 

 sea water as the cells die. The increase in proportion of nitrogen in the final stages of 

 decomposition may be due to two causes — (1) either by the destruction of nonnitroge- 



