168 PROVASOLI [CHAP. S 



Most water organisms are bound forever to the water environment and the 

 cycle of organic matter is intimately dependent upon their activities. Lucas's 

 theory of "non-predatory" relationships between water organisms includes an 

 important part of these events because in waters the food chain is simul- 

 taneously a food pyramid and a pile of assorted excretions and metabolic 

 products of micro-organisms, plants and animals. These organic substances 

 fully express their biological activity because they are soluble or coupled in 

 various ways to hydrophilic molecules and freely diffusible in the continuum 

 of rivers, lakes and seas. 



The other sources of organic matter in the sea are the rivers, which carry in 

 the left-overs of the activities of fresh-water organisms, the elutes of rocks, and 

 leachings of soils rich in trace metals and in the chemical residues of the activity 

 of terrigenous microbes, plants and animals. Fluvial contributions to the open 

 seas are minimal, and if felt at all, must be long-term ; but they are significant 

 locally, particularly in locations such as great rivers ending in relatively land- 

 locked parts of the sea. One example is the effect of rivers and the effluent 

 from Lake Okichobee after heavy rains on blooms of Gymnodinium breve 

 (Wilson and Collier, 1955). Therefore quantitatively the plankton, especially 

 the phytoplankton which represents the bulk of life, is the main source of 

 organic matter in the sea, either through its secretions or decomposition. 



The fate of the organic substances thus produced, and therefore the quanti- 

 ties of organic substances actually found in the waters, depends on the kinetics 

 of production and consumption. Only slowly metabolizable organic substances 

 should tend to accumulate and, being in larger quantities, may be easier to 

 extract. Though these substances are of little or no nutritional value, they may 

 have important functions such as the solubilization and chelation of trace metals 

 (Shapiro, 1957; Fogg and Westlake, 1955); antibiosis, CO2 and rH buffering; 

 emulsification of fatty substances ; and chemical conditioning of sexuality, 

 spawning, moulting, etc. Such substances do accumulate in fresh waters as the 

 humic substances, the yellow acids (Shapiro, 1957) and peptides (Domogalla, 

 Juday and Peterson, 1925). In sea-water the situation seems to be different: 

 the C/N ratio of the organic solutes is low (2-6) while in fresh waters it is high 

 ( > 10). This difference may, however, be only apparent, because in the sea 

 the origin of the soluble organics is almost entirely autochthonous (from 

 organisms) while in fresh waters the effect of the surrounding soil and its leach- 

 ings are very important (see discussion on page 173). 



Conversely, organic substances which are in continuous demand as nutrients 

 should be present in small quantities. Direct chemical analysis of the waters 

 can be of little' \ise ; studies of turnover of labeled compounds seem more 

 helpful. Granted that most of the inherent difficulties of identifying and 

 following the fate of a variety of organic compounds in sea-water remain, this 

 analysis is inescapable if we want to trace the important chemical events in 

 the environment. The important thing is to know what is worth tracing. 



Since we are dealing with knowns and unknowns produced by organisms, 

 we must go to the origin, to the aseptic cultures of the organisms themselves : 



