The term "bloom" used in this paper follows 

 the definition by Finucane (1964): "Any con- 

 centration of G. breve exceeding the normal 

 population level of approximately 1,000 cells 

 per liter." During previous red-tide studies, 

 lethal blooms of G. breve usually consisted of 

 250,000 organisms per liter or more (Finucane 

 and Dragovich, 1959). 



DISTRIBUTION OF GYMNODINIUM BREVE 



The distribution of phytoplankton may be 

 portrayed as 4-dimensional, consisting of 

 latitudinal, longitudinal, vertical, and temporal 

 components. In this paper, distribution is 

 examined primarily in the light of previous 

 studies of the Florida red tide (Dragovich, 

 1961; Finucane, 1964). 



Geographic Distribution 



G. breve was found in 24 percent of all 

 samples, and was present in one or more 

 collections at all offshore stations in concen- 

 trations of <10 to 53,800 cells per liter (figs. 

 2a, 2b, 2c, and 2d). The scale shown in the 

 legend of the figure represents only one-half 

 of the profiles; September values are shown 

 with interrupted lines because they exceed 

 scale. The top value (September) represents 

 the number of cells at the surface; the lower, 

 cells at 5 m. 



The percentage of samples in which G. breve 

 occurred (hereafter identified as incidence) 

 was highest (32.3 percent) at stations off 

 Venice Inlet, lowest at stations off Boca Grande 

 Pass (23.0 percent), and intermediate off Anna 

 Maria Key (29.7 percent) and Johns Pass 

 (29.0 percent). In terms of distance from 

 shore, incidence of G. breve was highest at the 

 27.8-km. (15-mile) stations and least at the 

 9.3-km. (5-mile) stations (fig. 3). 



G. breve was absent from all Tampa Bay 

 samples and was recorded at Charlotte Harbor 

 only in April and July, in concentrations of 

 less than 100 cells per liter. 



Monthly Occurrence 



Counts of G. breve were less than 1,000 per 

 liter in each month except February and Sep- 

 tember. After the high incidence in February 

 1964, numbers declined in March and April 

 and remained relatively low through August. 

 Both numbers and incidence increased at all 

 offshore stations in September, and cell counts 

 were higher than in any previous month. 

 Numbers decreased in October and November, 

 when monthly incidence was the lowest during 

 the study. Both numbers and incidence in- 

 creased again in December. The incidence in 

 that month was highest 27.8 km. (15 miles) 

 and 37.1 km. (20 miles) offshore from Johns 

 Pass, Anna Maria Key, and Venice Inlet; 

 samples off Boca Grande yielded no G. breve . 

 Adverse weather in January and February 

 1965 prevented collections at some stations, 

 but in the areas sampled (Tampa Bay, Johns 

 Pass, and Venice Inlet), the incidence of G. 

 breve was low. 



Vertical Distribution 



G. breve was collected at least once during 

 the study at each offshore station and each 

 sampling level. The highest incidence of the 

 organism was at the surface (33.3 percent) and 

 at 5 m. (30.5 percent), lowest at 20 m. (20.7 

 percent), and intermediate at the 10- and 15-m. 

 levels. Samples containing 1,000 cells or more 

 per liter were recorded only at the surface 

 and at 5 m. (figs. 2a and 2c); 67 percent of 

 these high counts were at the surface. Finucane 

 (1964) also observed higher incidence of G. 

 breve at the surface than at the bottom. 



