PART VIII — AQUATIC ECOSYSTEMS 



2. OCEANIC PRODUCTION 



Primary Plant and Animal Life in the World Ocean 



Aquatic Plants 



In the sea as well as on land, the 

 primary producers of organic matter 

 are plants. It is estimated that 

 roughly 20 billion metric tons of 

 carbon is fixed by photosynthesis 

 in the sea each year. This amount 

 of carbon fixed annually should not 

 be confused with the total amount 

 of plants, in terms of carbon weight, 

 existing at any one time. Since the 

 process of organic production takes 

 place at a rapid rate in the sea, the 

 average standing crop of plants is a 

 small fraction of the annual produc- 

 tion. This makes a sharp contrast to 

 the plant production on land. The 

 total quantity of terrestrial plants 

 present at any one time is, on the 

 average, much greater than the an- 

 nual production. 



Potential Use by Man — Another 

 striking difference between oceanic 

 plants and terrestrial plants is in 

 their size and distribution. The vast 

 majority of plants in the sea are 

 microscopic single-cell algae (see Fig- 

 ure VIII— 4) in contrast to the grass, 

 crops, shrubs, and trees that form the 

 bulk of terrestrial vegetation. These 

 small organisms, collectively called 

 phytoplankton, are diffused over vast 

 areas of the ocean. Even the great- 

 est concentrations of phytoplankton, 

 which occur in productive areas at 

 certain times, are nothing compared 

 with the density of plants in green 

 land areas. The enormous expense of 

 collecting these diffused, single-cell 

 organisms from sea water makes har- 

 vesting of marine plants for man's 

 use completely uneconomical. Fur- 

 thermore, many of the dominant spe- 

 cies of phytoplankton have hard 

 siliceous or calcareous skeletons that 

 make them unpalatable to man. For 

 these and many other reasons, the 



use of phytoplankton as an important 

 source of food appears quite out of 

 the question. 



There are various seaweeds and 

 other large aquatic plants, some of 

 which are used for food or for man- 

 ufacturing industrial products. Most 

 of them, however, are attached to the 

 bottom and therefore confined to 

 shallow inshore waters. The total 

 yield (in wet weight) of these plants 

 for all purposes from the world ocean 

 is about 900,000 metric tons a year, 

 or approximately 1.5 percent of the 

 total landings of marine fisheries. 

 More than half of this amount is 

 harvested in Japan. Harvesting of 

 large aquatic plants could be increased 

 greatly, but its contribution to the 

 supply of plant food as a whole 

 would be insignificant. 



The Role of Phytoplankton — The 

 infeasibility of using phytoplankton 

 for food or other purposes does not, 

 of course, affect their basic role in 

 the economy of the sea. Animals can- 

 not manufacture living substance 

 from inorganic materials. They de- 

 rive it directly by grazing on plants 

 or indirectly by eating other animals 

 that have eaten plants. Thus, the 

 amount of carbon fixed by plants 

 (measured by 14 C methods) is widely 

 used for evaluating the basic produc- 

 tive capacity of the sea. On a global 

 scale, it may be used for roughly 

 estimating the potential harvest of 

 the sea. Starting with the total fixa- 

 tion of organic carbon and using 

 various assumptions on the efficiency 

 of energy transfer, one can theoreti- 

 cally arrive at estimated harvestable 

 outputs at different levels of the 

 food chain. Estimates obtained by 

 this method vary widely, depending 

 on the assumptions used. Neverthe- 

 less, they indicate a general range 

 within which the potential harvest of 



the sea should fall, as well as the 

 sources of inaccuracy inherent in 

 this method. 



It has been demonstrated that, 

 among the areas where intensive ex- 

 ploitation of living resources has been 

 taking place, areas of high primary 

 productivities generally coincide with 

 those of high yields from fisheries. 

 Such primary productivity data by 

 area are useful in a variety of ways. 

 Used in combination with catch stat- 

 istics in heavily exploited areas, they 

 provide means to test the validity 

 of various assumptions on the effici- 

 ency of energy transfer, particularly 

 when data on secondary production 

 (i.e., zooplankton) are also available. 

 They also indicate some of the areas 

 that are grossly underexploited but 

 in which abundant potential re- 

 sources are likely to occur, as is the 

 case with certain parts of the Indian 

 Ocean, the tropical Pacific, and the 

 South Pacific. When such informa- 

 tion is combined with data on the 

 forms of animals likely to be abun- 

 dant in the respective areas, it will 

 provide a substantial scientific basis 

 for planning the exploration and ex- 

 ploitation of such areas in order to 

 extract greater amounts of animal 

 protein material from the sea. Also, 

 the differences in primary produc- 

 tivity between areas are such (1:50) 

 that there are many areas in the 

 world ocean that could be written 

 off, based on productivity data alone, 

 as potential fishing grounds for large- 

 scale industrial operations. 



Numerous measurements of pri- 

 mary production have been made, 

 but they are largely in the limited 

 areas of the world ocean, and data 

 are quite scarce for most other parts. 

 It would be desirable to incorporate 

 primary production measurements in 



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