THE IMPENETRABLE SEA 



Scientists find it extremely difficult to make cut-and- 

 dried classifications of the habitats of the creatures of the 

 sea. The lower deeps merge into the middle deeps and 

 these into the surface waters, while these again blend 

 with the waters over the continental shelves, which yet 

 again pass without rigid demarcation lines into the 

 borders of the sea : its shallows and shore-edges. So with 

 the creatures themselves, for classifications tend to be 

 arbitrary, and the countless species, from the lowest forms 

 up to sea-mammals merge together with imperceptible 

 graduations, like the colours of a rainbow. 



There is one region which can be treated as a sharply 

 defined area, capable of simpler classification : the shore 

 between tide-marks. In this area the conditions of life are 

 unique, so that it is to be expected that the plants and 

 animals inhabiting the area will not be found elsewhere. 

 Jelly-fish are, in a sense, invaders of this clearly defined 

 area — they are stranded upon it rather than inhabitants 

 of it. 



Shore life presents animals and plants with peculiar 

 problems. These are mainly due to the fluctuating con- 

 ditions obtaining between tide-marks. Covered and un- 

 covered twice every twenty-four hours, by the ebb and 

 flow of the tide, the shore creatures live surrounded or 

 lapped by sea water when the tide is in, and subjected 

 to the influence of the local climate with its air conditions 

 when the tide is out. Rocks on the shore often become 

 extremely hot — even hotter than the air above them — 

 as when some rocks near Plymouth, England, during a 

 recent summer, showed a temperature of 120 degrees, 

 too hot for human feet. Yet sea creatures such as limpets 

 and barnacles on the rock, which had been chilled by 

 the sea some hours before, were alive and well. Rain is 

 another challenge to the hardihood of intertidal animals 

 and plants. 



As a general rule — although a few creatures like eels 

 and salmon are the exceptions — land forms die when 



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