SECT. 2J ORGANIC REGULATION OF PHYTOPLANKTON FERTILITY 171 



or contain inhibitory substances for the test species. When sufficient nutritional 

 information is available for a group of organisms, we can add to freshly collected 

 samples of waters (with their living population) a mixture of all the nutrients 

 required, the mixture minus one of the nutrients, and each single nutrient. We 

 have thus a means of discerning the lack of some nutrients and of evaluating by 

 the incidence of scarcity, which parameter is more ecologically important. 

 Other profitable uses of this approach can be found : H. Kylin (1941), employing 

 germlings of Ulva, found that waters of 70-m depth were low in N, P, Fe, Zn, 

 Co, Mn ; A. Kylin (1943) determined the need of them and level of trace metals 

 favorable for Ulva. 



2. Data from Chemical Analysis 



A . Quantities of Organic Matter in the Seas 



Organic matter into water is arbitrarily divided into : (a) particulate (living 

 organisms + detritus = seston) and (b) "dissolved" organic matter (in general 

 particles < 1 ll). Strikingly, the amount of dissolved organics exceeds by 

 many orders of magnitude the amount of particulate : in the euphotic zone, 

 rich in phytoplankton, it is seven to eight times greater and in deep waters, in 

 which the plankton is scarce, it may be up to a thousand or more times greater. 



Only recently has it been possible to analyze the dissolved organic carbon in 

 sea-water. The first reliable method was developed by Krogh and Keys (1934) ; 

 newer methods were developed by Kay (1954), Skopintsev (1959) and Duursma 

 (1960). Duursma, in a comprehensive, stimulating paper, reviews methods for 

 determining the dissolved organic Q, N and P in sea-water, the data obtained 

 and their significance. The quantities of total organic C in open seas vary from 

 0.2-2.7 mg C/l. Higher values are found in more landlocked areas : 3.3 in the 

 Black Sea, 4.6 in the Baltic, 6 in the Sea of Azov, and 8 in the landlocked 

 coastal area of the Dutch Wadden Sea (Table I). Contrary to the early data of 

 Krogh, who found an almost homogeneous distribution from surface to deep 

 water, wide variations were found by the other investigators. Especially 

 significant are the data of Duursma derived from several hundred analyses in 

 the Wadden, North and Norwegian Seas, and in the North Atlantic Ocean. He 

 found that "there are well defined areas where maximum and minimum con- 

 centrations occur, both horizontally and along the vertical" (Duursma, op. cit., 

 p. 133). Water-masses can be characterized by their peculiar concentrations in 

 organic nitrogen and carbon, besides the usual variations in salinity and tem- 

 perature. His distribution charts and data indicate that concentrations of 

 dissolved organics may permit the identification of smaller water -masses, 

 especially if one considers also the C/N ratios, which vary widely and in- 

 dependently. In a year's study of the station L.V. Texel in the North Sea, 

 Duursma found clear seasonal variation in dissolved organic matter. Since the 

 highest concentrations of organic C are reached several weeks after phyto- 

 plankton blooms, he considers that nearly all the dissolved organic compounds 

 are produced by breakdown of the dead phytoplankton and that the excretion 



