Papers in Marine Biology and Oceanography, Suppl. to vol. 3 of Deep-Sea Research, pp. 281-286. 



The production of antibiotics by plankton algae and its effect 

 upon bacterial activities in the sea * 



By E. Steemann Nielsen 

 Department of Botany, Royal Danish School of Pharmacy, Copenhagen 



Summary — Laboratory experiments with Chlorella and plankton diatoms show that small concen- 

 trations of the algae produce antibiotics which highly decrease the bacterial activities, including 

 respiration. If the concentration of organic matter is about the same as in natural sea water, the 

 decrease in bacterial respiration is of a much higher order of magnitude than the rate of photo- 

 synthesis of the algae. 



The normal light and dark bottle oxygen experiments cannot be used for measuring organic 

 productivity in oligotrophic water. Intense bacterial activities, which occur in the dark bottles as soon 

 as natural sea water is enclosed in the bottles, are much reduced in the light bottles; thus there is an 

 important difference in oxygen consumption between the two kinds of bottles, a difference which 

 has nothing to do with photosynthesis. The disagreement for tropical oceanic water between the 

 oxygen technique and the C-14 technique is thus easy to explain. 



It is suggested that the average age of the dissolved organic matter found in sea water is some 

 thousand years. This organic matter is most likely the most important food source— although 

 indirectly — for the bottom animals living at very great depths. 



INTRODUCTION 



In PRODUCTIVE coastal areas the so called " light and dark bottle " o.xygen experi- 

 ments originally introduced by Gaarder and Gran (1927) have been of great value 

 for estimating organic productivity by the phytoplankton. Riley (1939), however, 

 published results of such experiments lasting 3 days from the Sargasso Sea. which 

 according to ail evidence is one of the regions in the oceans most scarce in organic 

 life. According to Riley's measurements, this sea would be one of the most pro- 

 ductive sea areas of the world— if not the most productive. 



Steemann Nielsen (1954), by using the carbon-14 method, could not verify the 

 high rate of organic production in the Sargasso Sea. On the contrary, this sea was 

 found to be about the poorest area in all oceans regarding organic productions by 

 the plankton algae. This result, on the other hand, is in absolute agreement with 

 the general hydrographic conditions (minimum supply of nutrient salts), the low 

 standing crop of phyto- and zooplankton found, and the scarcity of fish. It could 

 further be shown that, theoretically, an organic production of the size claimed by 

 Riley must be considered impossible in the clear water of the Sargasso Sea, where 

 most light by far is absorbed by the water itself. The energy absorbed by the plankton 

 algae is only sufficient for a small photosynthetic rate. 



It could, however, be verified that the light and dark bottle oxygen cxpcnmcnis 

 give results comparable with those obtained by Riley. 



It is a well-known fact (cf. the next section) that the bacterial activities in sea water 

 are highly intensified if the water is enclosed in glass bottles. The respiration rates 



* Contribution No. 780 from the Woods Hole Oceanographic Institution. 



281 



