210 RILEY 



zooplankton, nekton, benthos, and bacteria. The nonliving fraction, generally 

 denoted as detritus, received scant attention. Much of what was said about it was 

 contradictory. For example, there was a common concept that the role of 

 decomposers was to degrade organic remains into progressively smaller particles 

 and eventually to dissolved organic matter and mineralized elements. However, 

 the most obvious detrital remains were the amorphous masses of material 

 referred to earlier, which could not by any stretch of the imagination be 

 identified as decomposing organisms. Detrital remains they might be, and are, in 

 the light of recent research, but there was no speculation as to the mode of 

 aggregation of small remains into larger masses. 



In general, this detritus tended to be regarded as of doubtful nutritional 

 value, but, paradoxically, many investigators regarded the so-called "rain of 

 detritus" as the chief nutritional supply for the sparse deep-sea fauna. Or 

 perhaps they were thinking more in terms of sinking bodies of dead copepods 

 and larger organisms, but few of these have been recovered in bathypelagic net 

 tows. 



In recent years, increasing attention has been given to the development of an 

 accurate description of nonliving organic matter in the sea, its possible roles in 

 the food web, and experimental studies that bear upon these matters. Detailed 

 discussion of the latter is given in the appendix, but some salient features may be 

 summarized briefly: 



1. Dissolved organic matter is not solely produced by bacterial activity. It is 

 also a product of extracellular liberation by algae 1 and zooplankton excre- 

 tion. These products include amino acids and other compounds of low 

 molecular weight that probably can be recycled directly into the food web via 

 heterotrophic uptake by small organisms and possibly by other pathways that 

 will be discussed later. 



2. Although the chief function of bacteria in the food web is the 

 decomposition of organic remains and eventual conversion to inorganic matter, 

 this is by no means a simple process. Bacteria also are capable of aggregating 

 small particles and possibly dissolved materials into flocculent masses that more 

 or less resemble naturally occurring aggregates. These masses can provide a 

 microcosmic environment for other small organisms and possibly a food 

 supplement for larger filter feeders. 



3. Small particles and probably dissolved organic matter can be adsorbed on 

 bubbles, producing flakes that are indistinguishable from those found in natural 

 seawater. Ultraviolet irradiation also stimulates particle formation. These 

 processes would be operative only in the immediate surface layer and may be 

 responsible for the observed fact that particulate organic carbon is several times 

 higher in surface film collections than in slightly deeper water. 



In short, it now appears that the interactions between living and nonliving 

 matter are more complicated than was formerly supposed and that a good many 

 of the reactions are reversible. 



