8 Marine Microbiology 



logical activities and also by the movements of water masses. 

 Upwelling, eddy diffusion, and vertical convection are especially 

 important in the transport of nutrient substances from deep 

 water to the euphotic zone. Harvey (15) reports concentrations 

 of some important nutrient elements in sea water as follows: 



There is considerable variation in the quantity as well as in 

 the kind of organic matter in sea water (9). Tlie concentration 

 of organic matter ranges roughly from 0.4 to 10 mg/liter in the 

 open sea and up to 100 mg/liter in shallow productive bays. From 

 60 to 85 per cent of this exists in a colloidal or other finely partic- 

 ulate state, generally less than 25 per cent in a dissolved con- 

 dition (13). Living cells, including plankton organisms, make up 

 a small fraction (usually less than 10%) of the total organic 

 matter, according to Fox et al. ( 12 ) who apply the term leptopel 

 to tlie colloidally or otherwise finely particulate suspended de- 

 tritus. Fox (11) estimates that the standing crop of organic 

 leptopel in the world's oceans exceeds by at least tenfold (per- 

 haps a hundredfold) the annual synthesis or standing crop of 

 total living marine organisms. 



An appreciable part of the organic leptopel consists of rela- 

 tively inert substances such as humus, chitin, lignin, cellulose, 

 complex proteins, and other refractory products along with par- 

 tially decomposed cellular materials. Dissolved organic substances 

 identified in sea water include traces of polypeptides, various 

 amino acids, organic acids, certain sugars, biotin, carotenoids, 

 enzymes, niacin, thiamine, and cobalamin (9, 56). The organic 

 content of sea water is in a state of constant flux, being continually 

 enriched by the organic remains, dissimilation products, and ex- 

 cretory materials from biota while losing organic substances 

 through assimilation, oxidation, mineralization, and other pro- 

 cesses. 



Despite the low concentration of organic matter in sea water, 

 it is a prime determinant of the growth of many kinds of micro- 



