20 Marine Microbiology 



ments. Small naked flagellates sometimes constitute a major bulk 

 of tlie biomass (52). Such nannoplankton appear to be very im- 

 portant as primary producers and as food for aquatic animals 

 (5). 



Autoti'ophic as well as heterotrophic microbes catalyze 

 countless chemical reactions which influence the states and cycles 

 of carbon, nitrogen, sulfiu", phosphorus, oxygen, and other ele- 

 ments in the sea. Some of these reactions influence the pH, Eh, 

 and other environmental conditions, particularly in sediments and 

 microzones. Bacteria are believed to be among the most important 

 dynamic agents in the diagenesis of marine sediments where 

 they play a role in the origin of oil. 



Although preponderantly beneficial, there are many ways 

 in which marine microbes are deleterious to the economy of the 

 sea or to the welfare of man (59). In this latter category is the 

 microbial spoilage of fish and the deterioration of man-made 

 structures. Many kinds of marine microorganisms contribute to 

 the fouling of submerged surfaces. Certain marine plants and 

 animals have been shown to be injured by microbial diseases and 

 maybe all higher aquatic organisms are susceptible to microbial 

 infections. In localized environments microbes sometimes vitiate 

 water by depleting dissolved oxygen or by producing hydrogen 

 sulfide or other toxic substances. 



CONCLUDING COMMENTS 



Such glimpses as we have gained of marine microorganisms 

 indicate that many kinds occur in aquatic environments where 

 they influence biological, chemical, and physicochemical condi- 

 tions. An accurate assessment of their significance awaits much 

 more information on their ecology, physiology, in situ reaction 

 rates, and other characteristics. New methods and new approaches 

 are needed to realize the great contributions that microbiology 

 has to make to oceanology and limnology, as well as to basic 

 biology. This symposium has already done much to take an in- 

 ventory of what is known and to delineate many of the unsolved 

 problems. It is hoped that these sessions will catalyze more active 

 interest in all aspects of aquatic microbiologv and help pave the 

 way for worldwide cooperation in studying the sea around us. 



