THE VEGETATION OF THE SEA 



OUR-FIFTHS of the surface of our globe is covered by- 

 salt water, and since all of the multitudes of animal 

 inhabitants of this vast aquatic environment are ulti- 

 mately dependent upon the photosynthetic plants, we 

 may say that in one sense the marine plants are the 

 most important of all the groups of organisms on earth. 



In the sea, extremes of climate are modulated by the water medium, 

 and the vastly predominant environment is one of monotonous dark- 

 ness and cold. Accordingly, the diversity of living things on the whole 

 is less than on the land, and while some groups are poorly repre- 

 sented, others are entirely lacking. Thus, whereas the highly devel- 

 oped mammals are sparsely represented in the sea and the insects 

 not at all, in the marine vegetation the seed plants and fungi are few 

 and the ferns and mosses absent. On the other hand, some of the 

 phyla of organisms present in the sea are absent on land, or much 

 less richly developed there. This is true of the several groups of plants 

 known as algae of which the great bulk of the marine vegetation is 

 composed. 



With the exception of the bacteria and of a few parasitic and 

 saprophytic fungi, virtually all of the marine plants are autophytic, that 

 is to say, independent and capable of providing their own food by 

 means of photosynthesis. To do this they need two primary raw ma- 

 terials, namely, water, which is seldom in short supply, and CO^. 

 Energy for the process of photosynthesis must be suppHed by sunlight 

 which, however, is largely absent in the sea. Most of the marine en- 

 vironment is totally lacking in sunlight which penetrates, even in the 

 most exceptionally clear water, only to as much as three or four hun- 

 dred feet. Accordingly, these autophytic plants are restricted in the 



IKTERTOAL PELAGIC 



INFRATIDAL 

 J»7 



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0""^'°'' PHOTIC 



ZONE 



benthk: nvisoN 



Fig. 1. Diagram of the general habitats of the plants of the sea. 



