ANIMAL LIFE IN THE SEA 159 
animals, are represented in the shore waters by many 
species—by more than in the open ocean. But, it 
may be asked, if these algae have no attachment to 
a substratum, how do they contrive to remain in 
the shore waters, in spite of currents and tides which 
must tend to sweep them seawards? The answer 
is apparently that myriads are so swept out into 
the ocean, but there they degenerate, and probably 
do not live long. Produced in the shore waters, their 
destiny may be to serve as food for the pelagic animals 
of the open seas, but they no more form a true part 
of the life of the pelagic area than does that shore- 
born weed which floats at the surface of the Sargasso 
Sea for a period, ere it perishes and is replaced by new 
fragments torn off by the currents. 
Of the physical peculiarities of the littoral area the 
constant movement of the waters is characteristic. 
Tides and currents, in all the open seas, ensure that no 
stagnation shall occur, and thus keep the water sweet, 
and bring constant supplies of food and oxygen. It is 
this constant movement which helps to give the shores 
of the oceans so much richer a fauna than the shores of 
lakes, or of enclosed seas like the Mediterranean or 
Black Sea. The constant movement brings with it 
also a danger, whose influence is manifest in several 
ways. Some of the shore forms are swift swimmers, 
strong to stem the tide, and yet, notwithstanding their 
strength, the shore naturalist knows that off many 
coasts he is sure of a rich harvest when wind enforces 
tide or current, for the beach at certain seasons is 
strewn with flotsam and jetsam. Many shore fish, the 
strong cuttles among molluscs, powerful forms like 
porpoises and dolphins and even whales—there are 
times when the strength of these avails them nothing 
