408 MARINE DINOFLAGELLATES AND RED WATER CONDITIONS 



Thus through the combined processes of floatation and surface con- 

 centration, a method is possible by means of which red water condi- 

 tions may be produced without the excessive enrichment of the water, 

 and, indeed, without an unusually heavy growth of dinoflagellates. 

 This may be illustrated by the following hypothetical situation. 



According to Riley (1937, 1938) phosphate-phosphorus values for 

 the surface waters of the Gulf of Mexico range from 0.02 to 0.5 micro- 

 gram atom per liter. Since red water often occurs when nutrient levels 

 are low, let us propose a situation in which the phosphate-phosphorus 

 concentration is 0.05 microgram atom or 1.55 X 10^® gram per liter. 

 Let us further assume that other mineral nutrients, organic growth 

 factors, etc., are present in the same or higher concentrations as 

 phosphorus relative to the requirements of a given species of dino- 

 flagellate. 



No data are available concerning the dry weight and elementary 

 analysis of red water organisms. However, these may be roughly 

 estimated from known figures for other plankton organisms, and values 

 may be obtained which are probably reliable within an order of 

 magnitude. 



Gymnodinium brevis, the dinoflagellate responsible for the Florida 

 red tide of 1946-47, measures approximately 28 by 28 by 13 mi- 

 crons (Davis, 1948), and its volume may be roughly estimated at 

 7.5 X 10-^ cc. If it is assumed to have about the same densit}^ as 

 sea water (at about 34<'/oo and 25° C in the coastal waters of the 

 Gulf of Mexico), its wet weight will approximate 7.7 X lO"'' gram per 

 cell. 



Ketchum and Redfield (1949) found that the dry weight of a va- 

 riety of planktonic algae was approximately 25% of their wet weight, 

 and that their phosphorus content was rather constant at about 2.5% 

 of the dry weight. Using these figures for Gymnodinium (which are 

 probably somewhat high for dinoflagellates in general) a value of 

 0.48 X 10^^^ gram of phosphorus per cell is obtained. 



A dissolved phosphorus concentration of 1.55 X 10"^ gram per liter 

 will then support a population of 



1.55 X 10-« 



0.48 X 10-10 



= .3.2 X 10" cells per liter 



