THE DEEP SEA ANIMALS 1 87 



large algae or sea-weeds of many sorts and flowering plants 

 living fastened to the bottom. These are constantly dying 

 and, partially decaying, breaking up into fine particles, this 

 detritus floating about in the water and finally coming to rest 

 in the mud or sand. The microscopic plants of the open ocean 

 of course exist here also, while many kinds of diatoms and 

 similar t>T3es live on the bottom and clinging to the weeds. 

 While a few animals here Hve by browsing on the sea-weeds 

 and the eel-grass, the dominant animal types are sluggish or 

 sessile, or attached and usually arborescent plant-like animals, 

 living on the bottom or traveUng over it consuming the de- 

 tritus, with the more active animals consuming them, espe- 

 cially the shell-tish, crustaceans and echinoderms. 



What happens as the sea floor sinks further and further from 

 the surface? 



The light gradually diminishes so that in the clearest and 

 most sunlit seas at about 650 feet there is only a pale moon- 

 light at noon on the brightest day, while at greater depths 

 there is no light at all. Wave motion dies away and not far 

 below the surface there is perpetual quiet even in the fiercest 

 hurricane. The temperature dechnes, rapidly at first and then 

 more slowly; in the abysses it is mostly a few degrees above 

 the freezing point — below it in some places. The pressure 

 increases so that at 15,000 feet it is about two and one-half 

 tons to the square inch. 



The number of kinds of animals found between tide marks, in 

 rock pools, on the beaches, or on piling, is relatively small, 

 rapidly increasing from the high to the low water mark. Be- 

 low the low tide mark the variety of animal life is markedly 

 increased. Beyond a slight depth, 50 feet or so, but varying 

 in different places, within which there are often well marked 

 zones, some of the shore forms disappear, but other creatures 

 take their places and still others constantly appear at greater 

 depths. The maximum variety of marine animal types is 

 found on bottoms between about 600 and 1200 feet where 

 the light is dim to almost absent, the water is cool and very 



