RELATION OF TEMPERATURE TO 

 OCCURRENCE OF GYMNODINIUM BREVE 



Several studies have been made on the 

 effect of temperatures on G. breve under field 

 conditions and in the laboratory. Aldrich(1959), 

 who studied the effect of temperature upon 

 bacteria-free cultures of G. breve , reported 

 some survival below 7° C. and a slowing down 

 at 15° C. Seven years of field data analyzed 

 by Rounsefell and Nelson (1964) indicated that 

 G. breve thrives frona 16° to 27° C, but that 

 outside this range the organism occurs only 

 in small numbers. The adverse effect of low 

 tennperature upon blooms of G. breve was 

 observed in 1957 (Finucane, 1958). Concen- 

 trations were reduced to a few cells per liter 

 after the water temperature dropped to 9.9'-' C. 



In our study, G. breve was observed at 

 temperatures from 13.8° to 30.6° C. The 

 highest numbers of samples containing the 

 organism were recorded within the ranges 

 from 14.0° to 15.9° C. and from 26.0° to 

 27.9° C. (table 3). Incidence was low at the 

 maximum and minimum temperatures. Cell 

 densities greater than 1,000 per liter were 

 recorded at 26.0° to 27.9° C. 



The relation between the occurrence of 

 G. breve and temperature is difficult to deter- 

 mine from our data because of the low inci- 

 dence and concentrations encountered. On 

 the basis of laboratory studies by Aldrich 

 (1959) and field observations by Finucane 

 (1964) and Rounsefell and Nelson (1964), the 

 temperatures observed were generally favor- 

 able for the proliferation of G. breve . The 



Table 3. — Temperature and salinity ranges within which G. breve occurred in the coastal waters of 



west Florida (February 1964 through February 1965) 



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