collecting 12 hours each through a strong 

 flood and ebb tide sequence. The plankton 

 taken was considered sufficient to feed 357 

 people a meal. It is not known whether equiva- 

 lent amounts could be obtained anywhere along 

 the American coast. Heavy concentrations of 

 plankton exist in polar regions, but harvesting 

 these would be hazardous owing to adverse 

 weather and would entail the added expense of 

 transporting the catches long distances for use 

 in the populous areas of the world, although 

 the bulk could be reduced to a minimum by 

 dehydrating the catch aboard factory ships. 

 Cropping plankton on a large scale for human 

 food might critically reduce the food supply 

 of fish, lobsters, clanns, whales, and other 

 fishery resources which now produce a world- 

 wide annual yield of 45 to 60 n-iillion tons of 

 choice foods. Yet some authorities estimate 

 that only about 10 percent of the ocean's 

 annual production is now being used, that the 

 present harvest could be increased from 1- 1/2 

 to 10 times by the use of more effectual fish- 

 ing gear, and that production could be increased 

 even more by cultivation and fertilization of the 

 water masses. 



Man scarcely can afford to jeopardize the 

 continuance and improvennent of this food 

 supply from the seas, lakes, and rivers by 

 competing directly with the aquatic aninnals for 

 their food. He may, more wisely, supply his 

 growing needs by cultivating the plankton 

 ashore in automated factories established 

 near markets, thus eliminating the problem of 

 collecting under adverse weather and sea 

 conditions. 



Phytoplankton can be cultured in vats wher- 

 ever water and proper light, temperature, and 

 nutrients are available, and the organisms can 

 then be floated off the nutrient into handy 

 containers. The single-celled alga, Chlorella , 

 which has the capacity for rapid growth, is 

 particularly well suited to artificial culture. 

 With suitable media and an appropriate ap- 

 paratus, a bloom can be generated as often as 

 nine times daily and these blooms can be re- 

 peated indefinitely. When algal food for human 

 consumption is produced under controlled con- 

 ditions, yields will be high and crops can be 

 harvested continuously by mechanical means 

 requiring a minimum of hunnan labor. Culture of 

 algae in the future may become a big business. 



At present, great strides are being made 

 toward producing, in a closed ecological sys- 

 tem with only a small amount of electrical 

 energy, sufficient algae to satisfy the food 

 requirements of one man in space travel and 

 to convert his wastes into nutrients for the 

 algae. 



Purification of Water Supplies 



The health of the people in a community is 

 influenced by the purity of the water they 

 drink; moderate numbers of algae help purify 



lake and stream waters. Algae use as nutrients 

 nitrogen and phosphorus compounds that have 

 been washed frona the land, and convert into 

 oxygen the carbon dioxide dissolved in the 

 water from the atmosphere and from the decay 

 of submerged organic matter. Blooming plank- 

 ton, because they feed on the inorganic solutes, 

 actually change the chemical composition of 

 the water. Nitrogen and phosphorus connpounds 

 normally are not abundant in most surface 

 waters, and a real scarcity of either compound 

 slows the growth of algae, thus gradually 

 diminishing their value for purification as the 

 season progresses. 



Excessive enrichment (pollution) of water 

 supplies, and consequent blooms of algae, has 

 emerged as a major problem in the purifica- 

 tion of water for human consumption in recent 

 times. The rate of removal of nutrient mate- 

 rials by biological means is dependent upon 

 the kind of planktonic organisms present and 

 upon the environnnental conditions; conse- 

 quently, the actual performances have been 

 erratic and unpredictable. Light intensity is 

 one of the critical factors. The minimum 

 requirement to produce rapid biological ex- 

 traction of phosphate appears to be about 100 

 to 200 foot-candles. Under normal conditions 

 adequate light intensities seldom are attained 

 in algal cultures in excess of a foot below the 

 surface; if the water is deeper than that, the 

 illumination decreases sharply . For these 

 reasons, in the treatment of wastes fronn urban 

 areas the purest water and the greatest return 

 of nutrients are obtained in industrial plants 

 where the best environmental conditions for the 

 algae and the most active species can be main- 

 tained. 



High fertility of the water need not neces- 

 sarily generate noxious blooms. On the Eni- 

 wetok coral reefs, where community produc- 

 tion was well balanced, E. P. Odum was 

 impressed not only by the importance of 

 water movement, but by the intimate asso- 

 ciation of algae with the corals and with many 

 other animals. This association was a highly 

 developed symbiosis (living together) of or- 

 ganisms, some (i.e., green plants, some bac- 

 teria, and true fungi) able to feed on simple 

 inorganic substances and others (i.e., animals, 

 some bacteria, and true fungi) dependent on 

 complex organic food materials which have 

 originated in other plants and animals. In this 

 environment lived, in addition, a large standing 

 crop of consumers including great numbers 

 of herbivorous fish, which, Odum believed, 

 "were capable of consuming algae as fast as 

 produced." This is an ideal situation with no 

 outside pollution that could not be duplicated 

 in the effluent from a modern city. 



Odum suggested that man "get into the food 

 chain" at the primary level not only to alle- 

 viate his crying need for additional foods but, 

 at the same time, to, "make use of the in- 

 creased productivity created by cities rather 



10 



