400 MARINE DINOFLAGELLATES AND RED WATER CONDITIONS 



here completely. Table II gives a partial review of the red water 

 literature, including the time and place of the occurrence, the causa- 

 tive organism, and a brief statement of the ecological conditions 

 preceding or accompanying the outbreak, in so far as these have been 

 observed. 



Prerequisites for Red Water Conditions 



The basic requirements for an outbreak of red water may be 

 summarized under the following three headings: (1) a seed popula- 

 tion of dinoHagellates, (2) the existence of favorable conditions for 

 the growth of one or more of the species present, and (3) either 

 the concentration of sufficient nutrients to permit the dense growth 

 of the organisms, or the concentration of the organisms tliemselves, 

 to the degree to which they are found in "red water." 



The presence of a seed population of dinoflagellates is a condition 

 which is probabh' always met, for there are at least a few of these 

 organisms in almost every part of the ocean at all times. However, this 

 is undoubtedly an important factor, together with the environmental 

 conditions, in determining the particular species of dinoflagellate 

 dominating a red water outbreak. Thus, it is somewhat more difficult 

 to account for the origin of Gijmnodinitim hrevis, the causative agent 

 of the Florida "red tide," which appears to be present in the region 

 only during its periods of blooming. Slobodkin ( personal communica- 

 tion) is of the opinion that seed populations of this organism are main- 

 tained in the brackish to freshwater regions of the Florida Everglades. 



In maximum developments of "red water," the optimal growth 

 conditions for the species involved are perhaps met or closely ap- 

 proached. However, such ideal situations are probably less common 

 than the existence of an environment in which the growth of some 

 one species of dinoflagellates is favored over that of all other phyto- 

 plankton forms. In most parts of the ocean the diatoms are the 

 principal competitors of the dinoflagellates, though other forms, such 

 as Chrysophceae, Chlorophyceae, and Euglenineae may be important 

 in estuarine conditions. 



In the preceding sections of this report we have seen that the 

 dinoflagellates can compete successfully with the diatoms under 

 conditions of high temperature, low sahnity, and reduced nutrient 



