OCEANOGRAPHY IN THE UNITED STATES 283 



making up bottom communities ; the first step in the animal food chain, 

 the zooplankton; and the hirger forms — fish and whales. The distri- 

 bution of interest and effort of these scientists is shown in table I. 



These basic biological processes are studied primarily because of the 

 interest and the curiosity of the scientists on our staff. There are also 

 eminently practical reasons for understanding the biological cycle in 

 the sea. These basic studies are necessary before we can understand, 

 much less modify, the yield of edible species of fish and other seafood. 

 Also, the living organisms in the ocean will limit the amounts of radio- 

 isotopes which w^e can safely add to the ocean, either as a waste-dis- 

 posal measure or inadvertently as a result of accidents. 



The cycle of life in the sea, just as on land, depends upon the process 

 of photosynthesis which converts the energy of the sun to living or- 

 ganic matter. In the clearest ocean water sufficient light to permit 

 photosynthesis may penetrate to depths of 300 feet. Here, however, 

 the bottom is perpetually in the dark and the microscopic phytoplank- 

 ton, which float freely in the water are the only plants which can live 

 in the upper, illuminated zone. The seaweed, so common along shore, 

 is limited to depths of 100 feet or so in our turbid coastal water by lack 

 of light. 



The essential fertilizing chemicals, such as phosphorus and nitrogen, 

 are greatly reduced and sometimes completely exhausted throughout 

 the illuminated zone. However, about 90 percent of the ocean water 

 is at greater depths and a tremendous reservoir of these essential ele- 

 ments is stored in these deep waters. In the higher latitudes, w^inter 

 cooling and strong winds mix the w^aters deeply and these fertilizers 

 are returned to the surface. In spring, as sunlight increases and the 

 water warms, the phytoplankton liave a rich medium in which to grow 

 and produce a spring bloom. In the tropics mixing occurs less deeply 

 and the surface waters are always low in nutrients. However, the 

 plants grow slowly throughout the year. Here the biologist and 

 physical oceanographers face common problems since it is the turbu- 

 lence and the rate of exchange of materials between layers in the sea 

 wdiich keep this system going. 



The animals of the sea depend upon this plant production as their 

 source of food. The tiny zooplankton animals filter the microscopic 

 plants from the w^ater, using the most intricate arrangements of modi- 

 fied limbs and mouthparts. The variety of zooplankton is remarkable. 

 All of the major groups of invertebrate forms of life are represented, 

 and many different feedings types are frequently found in a single 

 sample obtained with a fine mesh net. To date we have studied the 

 food requirements of only a few species of this enormous community. 

 Some depend entirely on the plants they can filter from the water 

 while others consume these plant eaters, to be eaten in turn by larger 

 animals, including fish. There is a loss in energy at each step in this 

 food chain. When many steps are involved the final animal product 

 may be a small fraction of the organic production by the plants. It 

 has been estimated for one of our great fishing gromids, Georges 

 Bank, that about a thousand pounds of organic material must be 

 produced by the microscopic plants to provide one pound of fish for 

 the table. 



Several estimates have been made comparing the fertility of the 

 oceans with that of the land areas of the earth. Beyond the shallow 



38170— 5& 19 



