the reduction of the organism to nonbloonn 

 levels when red-tide periods extend into a late 

 summer characterized by unusually high tem- 

 peratures or into a winter when unusually low 

 temperatures prevail. The optimal tempera- 

 tures for G. breve usually occur in spring 

 and fall. 



Another major factor which may influence 

 distribution of G. breve is water movennent 

 along the west coast of Florida. Preliminary 

 hydrographic studies in the coastal waters 

 from Naples to Sanibel Island indicated the 

 presence of a south to north current in rela- 

 tively shallow waters. The findings agree with 

 Hela (1956), who found a northbound current 

 along the Florida southwest coast. Hela also 

 postulated that red tides always start in the 

 south and move northward. Our data on G_. 

 breve distribution indicate that this is not 

 necessarily true. During the 1957 outbreak, 

 the opposite (north to south) distributional pat- 

 tern was evident. At the beginning of the out- 

 break, most G^. breve and most of the fish 

 kills occurred in area A, the Tarpon Springs- 

 St. Petersburg section. This was followed by 

 a more southerly incidence of G^. breve in the 



estuarine and neritic waters of areas B and C 

 during the remainder of the year. 



Our data indicate higher concentrations near 

 the surface during daylight hours (fig. 7). 

 Phototropism of G^. breve in nature and in 

 the laboratory was observed also by Hela (1 956) 

 and Aldrich (1962). Further laboratory studies 

 by Aldrich (unpublished results)2 showed that 

 G. breve survived for a few days without light 

 and that populations maintained at a low light 

 level (200/foot-candles) declined. This sug- 

 gests that survival and vertical distribution of 

 G. breve in nature depend on solar radiation. 



Our investigation of the distribution of 

 G. breve has established the range of the 

 organism along the Florida west coast and 

 described certainhydrographic and meteorolo- 

 gical conditions existing during bloom and non- 

 bloom periods. Further studies of this or- 

 ganism would be necessary to fully understand 

 its environmental requirements and possible 

 means of control. 



^David V. Aldrich. 1960. Physiology of the Florida 

 Red Tide Organism. U.S. Fish and Wildlife Service, Bu- 

 reau of Commercial Fisheries, Clr. 92, p. 42. 



Table 4. --Monthly and annual total precipitation in inches at selected locations along the west 



Florida coast (1954-57)^ 



1954 



Area C 

 Everglades 



Area u 

 Tavemier 



Area A 

 Tampa 



Area B 

 Punta Gorda 



Month 



TOTAL 



Precipitation 



43.20 (49.94) 



Precipitation 



49.33 (50.76) 



64.35 (51.40) 



56.31 (47.63) 



1955 



12 



