402 MARINE DINOFLAGELLATES AND RED WATER CONDITIONS 



It is quite likely, however, that land drainage is important to the 

 dinoflagellates from another aspect, that of providing their necessary 

 organic matter. Whatever the function of these substances, it is possi- 

 ble that they are required in such minute concentrations as to satisfy 

 the requirements of the organisms, although the entraining fresh- 

 water may not appreciably dilute the sea water. 



The concentration of dissolved nutrient salts in a given water mass 

 prior to the onset of red water has not, to the author's knowledge, 

 been determined. There are, to be sure, small, local occurrences 

 which appear to be related to the introduction of domestic pollutants 

 (Braarud, 1945; Connell and Cross, 1950). In these instances there are 

 perhaps sufficient nutrients, as well as the necessary organic growth 

 factors, to support populations approaching red water proportions. 

 However, in the majority of red water occurrences there is no indica- 

 tion of an unusually high enrichment of the water prior to the out- 

 break. 



Brongersma-Sanders ( 1948 ) emphasized that red water is associated 

 with those regions of the world where upwelling brings deep, cold, 

 nutrient-rich water to the surface (i.e.. Southwest Africa, Peru, Cali- 

 fornia). She also pointed out, however, that such upwelled water 

 normally supports a luxuriant growth of diatoms, and that red water 

 occurs in these regions only during the summer months when upwel- 

 ling, and presumably the nutrient level, is greatly reduced. On the 

 Indian coast, the southwest monsoon is associated with high enrich- 

 ment and maximum productivity of the waters. Under these condi- 

 tions it is again the diatoms which flourish, and red water appears 

 only when the monsoon has ended. 



Ketchum and Keen (1948) measured the total phosphorus content 

 of sea water collected in and outside of patches of red water which 

 occurred off the west coast of Florida in 1946-47. They found con- 

 centrations of total phosphorus in the red water (including that 

 contained in the organisms) up to ten times as high as that of the 

 clear water outside of the local patches. These authors emphasize 

 the necessity for a mechanism either for accumulating these concen- 

 trations of phosphorus in the water prior to the growth of the organ- 

 isms, or for concentrating the organisms after they have grown. 

 There was no indication that the first of these alternatives was true. 



