22 



NATURAL HISTORY 



numerous crustaceans mostly copepods, jellyfish, and the larvae of 

 many crustaceans, molluscs, and fish. Some of the plankton, such 

 as small crustaceans, tunicates, medusae, small fishes, and larger 

 algae, may be visible to the naked eye, but most of it is microscopic. 



iV. y. Siaie Conseruation Dept. 



Comparison of the distribution of nannoplankton (minute forms that will 

 pass through the meshes of a plankton net) at the surface and bottom of four 

 Adirondack lakes. 



The larger pelagic organisms mostly found in the ocean, such as fish, 

 squid, whales, turtles, and seals, are called collectively nekton. 



Currents, wind action, the shapes of bays and coasts, migrations 

 of various animals, all cause differences in the horizontal distribution 

 of plankton. Sometimes given forms, as Cladocera, will multiply very 

 rapidly, even coloring the water in a large area. The vertical dis- 

 tribution is much more regular with reference to plants, since algae 

 and other green plants depend upon sunlight. Plants get very little 

 light at a depth of 100 meters. At 75 meters' depth, only half as many 

 plants are found as at 50 meters, and careful investigation in various 

 areas shows that most of the plant plankton lives within a few feet 

 of the surface. On the other hand, animals exist at great depths. 

 Beebe reports jellyfish, shrimps, and other plankton at a depth of 

 over 1000 feet and the tunicate, Salpa, as well as fishes, at his greatest 

 depth of 3028 feet. Dredgings from the "Challenger" and other 

 expeditions reveal many living organisms, particularly protozoans, 

 in the abysmal depths. 



