ORGANIC PRODUCTION BY PLANKTON ALGAE, AND ITS ENVIRONMENTAL CONTROL 



John H . Ryther 

 Woods Hole Oceanographic Institution 



Roughly three quarters of the earth's surface 

 is inhabited by an algal flora. Only on land and in 

 a few shallow water areas do the higher plants pre- 

 vail . Does it follow, then, that the non-vascular 

 plants dominate the earth in terms of the biomass 

 and productive capacity? In some coastal waters 

 there are vast beds of giant seaweeds representing 

 several thousands of grams of organic matter per 

 square meter (i.e. Blinks, 195 4), some of the 

 densest stands of vegetation known. However, 

 over 99% of the oceans are too deep to permit the 

 growth of attached plants and the flora is repre- 

 sented almost entirely by the microscopic, unicell- 

 ular algae, the so-called phytoplankton . The sole 

 exception to this is the sporadic occurrence of 

 floating seaweeds which may accumulate locally, 

 as in the Sargasso Sea, but are quantitatively in- 

 significant in the oceans as a whole. 



There have been but few attempts to measure 

 directly the standing crop, in terms of biomass, of 

 the phytoplankton . But there have been a large 

 number of measurements of their photosynthetic 

 pigments, particularly during 1957 - 1958, as part 

 of the oceanographic program of the International 

 Geophysical Year . Chlorophyll a values for the 

 upper, illuminated layers of the Atlantic Ocean 

 were found to range usually between .1 and .5 

 mg/m , averaging perhaps .25 . If we may assume 

 a chlorophyll a^:dry weight relationship of 1:100 in 

 phytoplankton (Harris and Riley, 195 6) the dry 

 weight/m of phytoplankton to a depth of 100 

 meters averages no more than 2.5 grams. Adding 

 a generous .5 grams to allow for the richer coastal 

 waters and to include the benthic algae, the oceans 

 support an average standing crop of about 3 .0 g/m 

 or, for the 361 x 10 kmof the hydrosphere, a 

 total weight of some 1 .1 x 10 ■'■^kg . 



From various sources (Schroeder, 1919; 

 Fawcett, 1930; Show, 1949; Brown, 1956) we may 

 divide the land surface into the following relative 

 proportions: 



1. Wasteland (desert, artic regions , 



mountains) 50% 



2. Cultivated land, grasses, sedges, 



brush, etc. 20% 



3. Forests 30% 



Let us assume that the first category, half 

 of the land area, supports a negligible fraction 



of its vegetation. From various agricultural statis- 

 tics, crop yields were found to average about 1000 

 g/m /year. According to Pearsall and Gorham 

 (1956) natural stands of grasses, sedges, bracken, 

 etc. produce from 400 to 1400 g/m /year, about 

 the same as cultivated land. Since these crops are 

 seasonal in most of the world, the average standing 

 crop on an annual basis would be less, perhaps 

 5 0% of the annual production. The mean standing 

 crop of this second category may be taken, then, 

 as 5 00 g/m^ over an area of roughly 30 x 10 km 

 for a total biomass of 1.5 x lO-'-'^kg. 



Ovington and Pearsall (1956) have estimated 

 the annual production of forest trees in Great 

 Britain from the weight of selected samples and the 

 age of the trees . Working backwards from their 

 data , the standing crop of their forest trees was 

 found to range from 10,000 to 40,000 g/m^ , an 

 average of 25 ,000 g/m . Extropolating this to the 

 45 X 10 km of the world's forests, we may esti- 

 mate a crop of trees of 1.1 x lO-'-^kg. 



Summarizing these standing crop estimates, 

 we have: 



Oceans 

 Land 



Wasteland 



Crops, grasses, etc. 



Forest 



1.1 X 10-^ ^kg. 



1.5 X lO^^kg, 

 1.1 X lO^^kg, 



Thus it appears that the higher plants , oc- 

 cupying no more than 1/8 of the area inhabited by 

 the algae, maintain a biomass more than 1,000 

 times greater. Crude though these figures may be, 

 they probably minimize the contrast between the 

 two plant groups, since the values for the aquatic 

 plants, if anything, have been exaggerated, while 

 the terrestrial stands were probably underestimated. 



What of the productive capacity of the land 

 and sea ? Does it follow that the algae are equally 

 insignificant in the annual production of the earth's 

 organic matter? There have been several recent 

 studies of organic production in restricted marine 

 areas on an annual basis (Steemann Nielsen, 1937, 

 1951; Riley, 1956, 1958; Ryther and Yentsch, 1958; 

 Menzel and Ryther, in press), and many more scat- 

 tered single observations in different parts of the 

 world's oceans (i.e. Riley etal, 1949; Steeman 

 Nielsen and Jensen, 1957) . From these sources, 

 we may place the mean value for net oceanic 



Contribution No. 1049 from the Woods Hole Oceanographic Institution and Contribution No. 

 from the Bermuda Biological Station. Supported in part by contracts AT(30-1)-1918 and AT(30-l)-2078 

 with the U.S. Atomic Energy Commission and by NSF Research Grant G-3234. 



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