PARTICULATE AND DISSOLVED ORGANIC CARBON IN OCEANS 21 1 



Organic aggregates in seawater harbor an abundant population of bacteria, 

 small algae that presumably are heterotrophic, at least in deep water, and 

 protista. 7 Their sources of nutrition have not been well established. The 

 possibilities include utilization of some parts of the aggregates, absorption of 

 dissolved organics, or a slightly more complicated mechanism in which 

 adsorptive accretion of the particulate fraction is balanced by browsing activities 

 of the heterotrophs. 



Pomeroy and Johannes 7 measured the respiratory requirements of this 

 so-called ultraplankton and obtained fairly large values, possibly equalling that 

 of the larger zooplankton. They estimated that total carbon utilization by 

 surface and mid-depth ultraplankton was approximately equal to "uncorrected" 

 14 C values for phytoplankton production. 



The last statement requires some explanation. The routine method for 

 measuring 14 C uptake has been criticized 21 because of errors due to 

 self -adsorption on filters. The International 14 C Laboratory at Charlottenlund 

 Slot has recommended that earlier results be increased by a factor of 1.45. In 

 addition, the 14 C measurements do not, of course, record photosynthetic 

 products that are liberated from the cells in soluble form. The combination of 

 these two factors might mean that primary productivity is 50 to 100% higher 

 than is indicated by ordinary 14 C values and therefore could account for the 

 needs of both ultraplankton and the larger zooplankton. 



The food requirements of mid-depth and deep-sea organisms and the role of 

 nonliving organic matter in the bathypelagic food web present some very 

 difficult problems. The "rain of detritus" theory has been challenged, 2 ' 3 and 

 it has been pointed out that much of the mid-depth fauna is migratory and is 

 capable of feeding on living organisms in the surface layer at night more 

 effectively than at the daytime level at mid-depths, thus physically transferring 

 food from the surface to deeper levels. Further, random vertical movements 

 below this level, with feeding and predation and death also randomized, would 

 lead to a net downward transfer of food via active predation and without, 

 necessarily, the mediation of sinking detritus. 



This theory goes to the opposite extreme, and the truth probably lies 

 somewhere between. Although most deep-water animals are predatory, there are 

 a good many copepods with foliaceous appendages suitable for a filter feeding 

 habit, although they might be feeding selectively as well. The guts of various 

 deep-sea animals have been examined, 24,25 and there is no doubt that they feed 

 on small heterotrophs. The copepods presumably are feeding on organic 

 aggregates with their microcosmic assemblages, for they could not filter 

 individual organisms of such small size with any degree of efficiency. However, 

 this would not necessarily be so in the case of pelagic tunicates discussed by 

 Fournier. 24 Harding 25 examined the gut contents of bathypelagic copepods and 

 found flakes and other nonliving components as well as small heterotrophs. 

 Histochemical staining procedures demonstrated a decrease in the protein 

 content of flakes between the foregut arid hindgut but little change in 



