1 88 THE BIOLOGY OF THE SEA-SHORE 



which are able to liberate nitrogen from its oxygen com- 

 pounds : in other words, to reverse the action of the nitrogen- 

 fixing bacteria ; and nitrifying bacteria, through whose 

 agency the nitrogen of the ammonia resulting from putre- 

 factive decomposition is " mineralised," i.e. oxidised and 

 combined with a base to form a nitric salt, and so rendered 

 available for marine plants. 



THE NUTRITION OF SHORE ORGANISMS IN PARTICULAR 



From the point of view of food-production the shallow 

 waters of the littoral are the most important in the whole 

 sea. As a result of drainage from the adjoining land the 

 quantity of ultimate food constituents, particularly the 

 essential nitrogen compounds, is relatively much greater 

 than in the open sea. This, of course, means an increased 

 amount of plant-life (both fixed and floating), which leads 

 in turn to a greater wealth of animal forms. One of the 

 fundamental reasons for the greater density of life in shallow 

 marine waters lies undoubtedly in the constant supply of 

 raw food materials washed down from the land. Shore 

 organisms get " first call " on this supply ; what is not 

 utilised by them is gradually dispersed by wind and tide 

 and serves to nourish life in the more open waters. 



The quantity of plankton in coastal waters has been said 

 to be thirty times as great as that in the open sea. These 

 waters, in fact, are the nursery where the development of 

 plankton, especially plant plankton, begins and whence it 

 spreads out gradually into the open sea (Allen, 1917). Over 

 and above this, they supply a quantity of fixed vegetation, 

 in the shape of the larger seaweeds, the development of 

 which is made possible by the presence of a substratum and 

 of adequate illumination. In the actual tidal zone the 

 advantages of this double food-supply are partly discounted 

 by the fact that feeding, except in permanent pools, is 

 necessarily intermittent. Perhaps the most eloquent com- 

 ment on this is the haste with which operations are resumed 

 when the water returns : barnacles and mussels beginning 



