JOHN H. RYTHER 397 



motility provides the dinoflagellates with an advantage in waters of 

 low nutrient content. The nonmotile diatoms are dependent upon 

 the dissolved nutrients contained in the water which immediately 

 surrounds them and through which they sink (see Munk and Riley, 

 1952). In contrast, the dinoflagellates, though not strong swimmers, 

 can move about for considerable distances and localize In the most 

 advantageous depth for photosynthesis. If the nutrient level of the 

 water is low, they may, by their vertical migrations, utilize all the 

 nutrients available within the entire photic zone. According to Peters 

 ( 1929 ) Cerotium can move through 5 to 10 meters in 12 hours or less. 

 Thus motility may be equally as important as the basic physiological 

 characteristics of dinoflagellates in providing the means for their 

 existence in waters of high temperature, low salinity, and reduced 

 nutrient concentration. 



"Red Water" Phenomena 



Background 



In certain parts of the world, usually in coastal or estuarine regions, 

 dinoflagellates either grow or aggregate to such an extent that they 

 impart a distinct coloration to the water. Such manifestations are 

 known popularly as "red tide" or "red water," since the predominant 

 color is of a reddish hue, although yellow or brown dinoflagellate 

 blooms are not uncommon. 



According to Allen (1946) a cell concentration of one-half to one 

 million organisms per liter may give a chocolate-brown color to the 

 water, while a doubling or trebling of this number is sufficient to 

 produce red water. Concentrations of over 50 million cells per liter 

 are not uncommon in patches of red water (Woodcock, 1948; Davis, 

 1948). 



Frequently these aggregations of dinoflagellates are accompanied 

 by a mass mortality of marine organisms (Whitelegge, 1891; Aiyar, 

 1936; Gunter et al., 1948; Connell and Cross, 1950). However, many 

 red water reports make no reference to such calamities. In many in- 

 stances these outbursts are also ac-companied by brilliant displays of 

 luminescence. 



The reported occurrences of red water are too numerous to review 



