ZoBeU 



76- 



Marine Microbiology 



other observed property of the water, Allen's (1937) data on the sea- 

 sonal distribution of phytoplankton off the La JoUa pier from 1920 

 through 1939 show that phytoplankton organisms vary in abundance 

 throughout the year much more than do bacteria. 



There is a definitely rhythmic seasonal cycle in the temperature of the 

 surface water at this latitude. Year after year the water temperature has 

 been observed to increase from a minimum of about 12° C. in the winter 

 months to a maximum of about 23° C. reached during the summer months, 

 but the abundance of bacteria in the surface water fails to parallel this 

 seasonal periodicity, except for short periods of time. 



Likewise the annual distribution of bacteria in surface sea water can- 

 not be correlated with the intensity of solar radiations. The latter has 



20 



5 3 

 O 



Fig. 9. — Seasonal distribution of bacteria (dotted line) in surface sea water 

 at La Jolla, California, based upon the average of daily plate counts from January 

 through December, 1933. The relative number of phytoplankton organisms per 

 liter of sea water (solid line) and the intensity of solar radiation (dashed line) are 

 also given. The latter was measured by the recording pyrheliometer at the Scripps 

 Institution. 



been measured continuously by an automatic recording pyrheliometer 

 which shows a definite seasonal cycle, the period of maximum insolation 

 at this latitude being from May through July. Minimal plate counts are 

 often observed during this period of maximum insolation as shown by the 

 curves in Figure 9, but during other years there is no semblance of cor- 

 relation between the abundance of bacteria in surface sea water and the 

 intensity of sunlight. 



The studies stress the importance of continuous and extensive obser- 

 vations preliminary to evaluating any single ecological factor. The com- 

 plexity of the factors influencing the marine environment is also illus- 

 trated by these studies on the seasonal distribution of bacteria. The com- 

 plexity of the marine environment is emphasized by Allen (1941) in his 

 ''Twenty years' statistical studies of marine plankton dinoflagellates of 

 southern California." 



Below the euphotic zone the marine environment appears to be highly 

 uniform throughout the year. One would not expect to find seasonal 



