The Immediate Tasks of Marine Microbiology 495 



microorganisms - nereids - fish. At present, the possihihty ol the 

 existence of shorter food chains is not excluded, characterizing 

 the nutritional importance of microorganisms at early stages in 

 the development of fishes. 



Much remains to be done to clarify the complicated and 

 varied inter-relations between microorganisms and phytoplank- 

 ton, plntol^enthos, zooplankton and zoobentlios in marine habi- 

 tats. Only very broad lines have so far been drawn, but even 

 those lines need confiniiation and correction. In the past, only 

 the relations between marine animals and plants and compara- 

 tively small groups of microorganisms belonging to heterotrophs, 

 which are able to develop only on the easily assimilable organic 

 matter have been studied. The use of direct methods opens new 

 possibilities in the study of these phenomena. The immediate 

 task, of interest also to planktonology, is a study of the dynamics 

 of microbial populations in connection with biological processes 

 of such importance in the seas and oceans as the diurnal migra- 

 tions of zooplankton and the "blooming" of phytoplankton. 



The progress of marine microbiology in explaining the regu- 

 larities underlying distribution of many biogenic substances in 

 seas and oceans is also still very insufficient. The obvious part 

 played by microorganisms in the biocatalytic changes of organic 

 and inorganic matter on land and in the ocean prompts hydro- 

 chemists and geochemists to expect from microbiology an ex- 

 planation of the causal relationsliips which determine the exist- 

 ing regularities in distribution of a number of chemical com- 

 pounds. However, the data of marine microbiology until re- 

 cently were often of a purely cjualitative character. It has been 

 established that in the water, and on the bottom of the seas, and 

 in the coastal areas of the oceans are found representati\ es ol 

 various physiological groups of microorganisms, taking direct 

 part in the carbon, nitrogen, phosphorus, sulphur, iron, man- 

 ganese, calcium cycles, but there are only few data as to what 

 numbers of these microbial forms are present and how acti\(> 

 they are. 



Wide scale investigations of the distribution of plixsiological 

 groups of microorganisms and the degree of their actixity were 

 carried out in the Black Sea, They were to elucidate the reasons 



