11G The Outline of Science 



the littoral area, and it is divisible into zones, each with its charac- 

 teristic population. It may be noted that the green seaweeds are 

 highest up on the shore; the brown ones come next; the beautiful 

 red ones are lowest. All of them have got green chlorophyll, 

 which enables them to utilise the sun's rays in photosynthesis ( i.e. 

 building up carbon compounds from air, water, and salts), but 

 in the brown and red seaweeds the green pigment is masked by 

 others. It is maintained by some botanists that these other pig- 

 ments enable their possessors to make more of the scantier light 

 in the deeper waters. However this may be, we must always 

 think of the shore-haunt as the seaweed-growing area. Directly 

 and indirectly the life of the shore animals is closely wrapped up 

 with the seaweeds, which afford food and foothold, and temper 

 the force of the waves. The minute fragments broken off from 

 seaweeds and from the sea-grass (a flowering plant called 

 Zostera) form a sort of nutritive sea-dust which is swept slowly 

 down the slope from the shore, to form a very useful deposit in 

 the quietness of deepish water. It is often found in the stomachs 

 of marine animals living a long way offshore. 



Conditions of Shore Life 



The littoral area as defined is not a large haunt of life; it 

 occupies only about 9 million square miles, a small fraction of the 

 197,000,000 of the whole earth's surface. But it is a very long 

 haunt, some 150,000 miles, winding in and out by bay and fiord, 

 estuary and creek. Where deep water comes close to cliffs there 

 may be no shore at all; in other places the relatively shallow 

 water, with seaweeds growing over the bottom, may extend out- 

 wards for miles. The nature of the shore varies greatly according 

 to the nature of the rocks, according to what the streams bring 

 down from inland, and according to the jetsam that is brought in 

 by the tides. The shore is a changeful place ; there is, in the upper 

 reaches, a striking difference between "tide in" and "tide out"; 

 there are vicissitudes due to storms, to freshwater floods, to 



