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Plant Biomass on Land and in the Sea. Rodin et al. (1975) estimate 
that the total weight of plant tissue (biomass) present on the land is 2.4 
x 1012 metric tons, dry weight. The total plant biomass in the world 
ocean amounts to 1.7 x 108 metric tons, which is about 15,000 times 
smaller than that of the land. Perhaps a better gauge of the relative im- 
portance of land and sea to the problem at hand is the rate of plant pro- 
duction. 
Plant Production of the Land and of the Sea. Primary production re- 
fers to the rate of production of organic matter through the photosynthesis 
of plants. Bogorov (1959) estimates that the total primary production of 
the land is 1.72 x 1011 metric tons per year, whereas that of the sea 
averages 5.8 x 1010 metric tons per year. Hence, the oceans with 
roughly three times the area of the land account for only one-third as much 
primary production as do terrestrial plant communities. What this adds up 
to, however, is the relative capacities of these two ecosystems to produce 
human food. The sea is a poor second. 
Food Producing Capacities of Land and Sea. The marine 71 percent of 
the earth's surface produces no more that 1.5 percent of the world's food 
supply, although it does contribute between 8 and 10 percent of the protein 
consumed by humans. Part of the reason for this disparity is the deficient 
protein level in the diet of the majority of humans. It is doubtful that 
the ocean's contribution to human food supplies will increase much in the 
future. In fact it may well decline. In 1978 world landings of ocean 
products totaled 72.4 million metric tons, which was down from the record 
74.7 million metric tons reported for 1976. The important point to note in 
regard to attempts to increase the food derived from the sea is that 99 
percent of it comes from nearshore (the estuarine/shelf complex) and only 1 
percent from the deep offshelf waters. The reason that the offshelf region 
yields so little (in the form of shark, tunas, and some squids) is not be- 
cause of the lack of exploitation but because it just is not there. The 
other discouraging fact is that most of the world catch is taken in waters 
less than 200m deep’and it is estimated that conmercial catches will at 
their deepest be no more than a 1000m. Compare this with the fact that 
