80 



70 - 



UJ 



< 

 I- 

 z 



o 



QC 

 UJ 



O. 40 



30 - 



20 - 



10 - 



2 



1954 



3 



ll 



SYMBOLS 



I 



2 

 3 



POSITIVE 

 POSITIVE 

 PAIRED 



-T — T- 



2 3 



1955 

 SURFACE 



I 



-T 



3 



1956 

 SAMPLES 



I 



2 



1957 



■T- 



3 



BOTTOM SAMPLES 



POSITIVE SAMPLES IN WHICH COUNTS 



WERE HIGHER AT THE SURFACE THAN AT THE 

 BOTTOM 



Figure 7. — Incidence of G. breve from simultaneously collected samples (1954-57). 



was below normal in the entire sannpling area. 

 During 1957, the other red-tide year, rainfall 

 was 10.29 and 20.49 inches above normal in 

 areas A and B respectively. The major red-tide 

 outbreaks in the fall and winter of 1954 and 

 1957 occurred in areas of abnormal rainfall. 

 These observations agree with the hypothesis 

 of Slobodkin (1953), who observed a close 

 association of red tide along the west coast of 

 Florida with periods of exceptionally heavy 

 rainfall. 



The seasonal occurrence and abundance of 

 G. breve may be associated directly or in- 

 directly with periods of heavy rainfall. In- 

 creased land drainage usually accompanies 

 these rainy periods, ultimately bringing more 

 nutrients into the adjoining estuaries and off- 

 shore waters (Harvey, 1957). Aldrich (1962) 

 stressed that vitamins, trace elements, and 

 chelators introduced by drainage waters into 



coastal environments were necessary to the 

 growth of G. breve . Dragovich and May (1962) 

 indicated that the mean copper concentrations 

 in river waters draining into Tampa Bay are 

 well below the levels toxic to G. breve . Bein 

 (1957) concluded that phosphates do not limit 

 the distribution of this organism because the 

 coastal waters of west Florida contain suf- 

 ficient phosphorus to support a red tide at all 

 times of the year. 



Salinity appears to have sonne association 

 with the distribution and abundance of this 

 organism, G^. breve was never observed in 

 high salinity >39,0%o waters south of Cape 

 Sable or in the upper portion of estuaries 

 having salinities less than 21 .0%o. The absence 

 of G, breve at salinities below 21 .0%o and above 

 38,9%o indicates that salinity may serve as a 

 barrier to its distribution. Lethal concentra- 

 tions of G. breve occurred only from 21,0- 



10 



