Publication Date:
2022-05-27
Description:
The paper examines the conventional notion of the food chain of the oceans in the light of field studies of microheterotrophic processes. In common with the earlier observations of POMEROY (1974), the conclusion is that the classical paradigm is not compatible with contemporary observations and appears to need extending in order to take them into account. The evidence would seem to point towards at least half of primary production passing through the planktonic microheterotrophs before it is mineralized. The possible routes of flow of organic material from the classical food chain (phytoplankton excretion, losses during grazing and zooplankton excretion) were examined in some detail. The conclusions were that the cumulative production of dissolved organic material from the above sources, estimated to amount to about 60% of primary production, are sufficient to sustain the anticipated rates of microheterotrophic activity. These considerations, by themelves, give no reason to seriously doubt the accuracy of contemporary measurements of primary production. It was calculated, given the present day estimates of microbial growth yields, that secondary production at the microbial level may be comparable to or greater than that of herbivorous zooplankton. When considering the sources of supply of organic material for the microheterotrophs, the events occurring prior to herbivore ingestion were found to be more important than those subsequent to ingestion. As a consequence, the overall accuracy of the estimates of the supply of organic material to the microheterotrophs was very much dependent upon the assessment of total phytoplankton exudation of organic material, i.e. the measured excretion plus that taken up by heterotrophic micro-organisms during the measurement period. The review also highlighted the need for a better understanding of the fate(s) of microbial production: to what extent it is utilized directly by metazoan hervibores as opposed to passing through a protozoan food chain.
Type:
Article
,
NonPeerReviewed
Format:
text
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