declines to the summer minimum at Bermuda. One 

 can assume from this alone that organic production 

 in the tropics is maintained at a low, rather steady 

 rate throughout the year, probably maintained by 

 the recycling of nutrients entirely within the eu- 

 photic zone, perhaps occasionally stimulated into 

 brief minor outbursts of growth by the limited mix- 

 ing action of storms . 



It is clear, then, that organic production in 

 the oceans is limited most of the time by either 

 light or nutrients . Both are available in plentiful 

 supply in the oceans as a whole, but both seldom 

 occur together. At the few times and places where 

 neither of these factors is limiting, production may 

 proceed at rates comparable to the highest levels 

 of production observed on land . 



As mentioned earlier, the concentrations of 

 nutrients in the tropics and semi-tropics are far 

 less than those present in the high latitude seas. 

 As a result much smaller populations of plants can 

 develop. Yet, due to the rapid turnover of these 

 materials , a low to moderate rate of production can 

 be maintained throughout a deep euphotic zone . If 

 one integrates production over the entire water col- 

 umn, the annual rate beneath a square meter of sea 

 surface is as high or higher than that of presumably 

 far richer waters . As an extreme example of this , 

 let us compare the vertical profile of photosynthe- 

 sis in the Sargasso Sea during a period of peak pro- 

 duction (April 19, 1958) with that of a shallow, 

 highly enriched sewage oxidation pond in South 

 Dakota (from Bartsch and Allum, 195 7) . The chlor- 

 ophyll concentration of the former averaged less 

 than 1 mg/m'^, the latter some 450 mg/m^ . The 

 oxygen production values of Bartsch and Allum have 

 been converted to carbon fixation assuming an 

 assimilatory quotient of 1.25 (Ryther , 1956b), and 

 the depth curve of photosynthesis has been rather 

 subjectively extrapolated to the surface. Exami- 

 nation of the depth profiles of daily production from 

 the sewage oxidation pond and the Sargasso Sea 

 (Figure 4) reveals an interesting fact . In the oxi- 

 dation pond, the euphotic zone is two orders of 

 magnitude smaller while production per unit volume 

 is two orders of magnitude greater than in the Sar- 

 gasso Sea . If one integrates the two curves, or- 

 ganic production beneath a square meter for the two 

 areas is found to differ by less than 20% . Actually, 

 the value for the oxidation pond is probably some- 

 what low, for the measurements were made from 

 10:00 a.m. to 3:00 p.m. rather than for an entire 

 day. But even if this figure is increased by 25% - 

 50%, the similarity between the two situations is 

 striking . 



This may appear to contradict the earlier 

 statement that production per unit area may be ex- 

 pected to increase with a decreasing euphotic zone. 

 It should be reiterated here that such is true only 

 in cases where living plants alone contribute to 

 the turbidity of the water . In a pond receiving raw 



sewage wastes, this would hardly be the case. 



But the point which I wish to make in com- 

 paring these two situations is this: that the daily 

 rate of production of organic matter, as it is cur- 

 rently defined by ecologists, is very nearly the 

 same in two bodies of water in which the amounts 

 of living plant material are respectively of the or- 

 der of 100 grams and 0.1 grams per cubic meter. 



AAHiat, then, does this rate of primary produc- 

 tion actually mean? One looks in vain for evidence 

 of it in the clear, blue waters of the Sargasso Sea . 

 The major fisheries of the world are located in the 

 temperate or high latitudes, or in the few regions of 

 divergences and upwellings which we discussed 

 above, not in places like the Sargasso Sea. Is it 

 realistic to compare fertility of northern and tropical 

 seas, of the ocean and the land, of a plankton 

 bloom and a cornfield, all on the basis of their rel- 

 ative rates of natural photosynthesis ? 



In modern, dynamic ecology, it has become 

 unfashionable to speak of the "standing crop" of 

 organisms . The important question is not "how 

 much is there?" but "how fast is it being produced?" 

 There is no doubt that this concept has opened up 

 new and extremely interesting avenues of ecologi- 

 cal research. But the population ecologist or fish- 

 eries biologist should beware of these values. The 

 sociologist who compares the productive capacity 

 of the land and sea may be sadly deluding himself. 

 For animals eat food, not photosynthesis. What is 

 the significance of organic matter which is produced, 

 consumed, decomposed and remineralized almost 

 simultaneously? Why add up a daily production 

 which is daily expended into a non-existent annual 

 total. Is this comparable to a barn full of corn? 

 The study of the rate of organic production has al- 

 ready and will continue to reveal fundamental phys- 

 iological and ecological principles . But the person 

 who examines these data with the hope of feeding 

 an overpopulated earth on marine resources would 

 do well to remember, when he picks a pound of 

 beans from his kitchen garden, that to get the same 

 weight of rather undigestable and unappetizing 

 plankton algae from the open sea, he would need to 

 filter some five million gallons of water. 



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