G. breve was widely distributed during the 

 year, although no blooms were noted. During 

 January-April, G. breve was present only in 

 the neritic waters of areas A, B, and C, from 

 Sarasota to Cape Romano. From May through 

 August, its distribution was primarily con- 

 fined to neritic waters in areas B and C, from 

 Sanibel Island to the Florida Everglages (fig. 

 6). During the remainder of the year, the 

 organism was distributed in both estuarine 

 and neritic waters in areas A, B, and C, 

 from Clearwater to Cape Romano. The G. 

 breve incidence during September-December 

 was higher during 1956 than in comparable 

 months of 1955 (table 1). 



1 957. --From January to September, G. breve 

 was observed in nonbloom numbers in areas 

 A, B, and C. These areas included Tampa Bay, 

 Sarasota Bay, Charlotte Harbor, San Carlos 

 Bay, the Florida Everglades, and their ad- 

 jacent neritic waters. E>uring March, G. breve 

 was found in area D off Cape Sable. This was 

 the only occurrence of the organism in area D. 



The incidence and numbers of G^. breve 

 increased in September and October, and 

 reached the highest proportions since 1954 

 (fig. 6). Dense concentrations (11,900-136,- 

 000/1.) were detected on Sept, 23 and 24 in 

 area A off Egmont Key and Clearwater. The 

 first fish kills of the 1957 red-tide outbreak 

 were reported off St. Petersburg Beach on 

 Sept. 26. From this date a progressive in- 

 crease in the number of blooms was observed 

 in areas A through C. G. breve counts as high 

 as 3,310,000/1. were noted off Anclote Key 

 (Tarpon Springs) by Oct, 4, During the same 

 month, blooms and fish kills occurred from 

 Sanibel Island to Naples in areas B and C. By 

 November, distribution of the organism ex- 

 tended as far south as the Shark River in the 

 Florida Everglades. As many as 1,100,000/1. 

 were present in water samples from Big Marco 

 Pass on Nov. 4. Blooms also were observed 

 in the estuarine and neritic waters extending 

 from Boca Ciega Bay (St. Petersburg) to Venice 

 in areas A and B. (fig. 6), 



Occurrence of G. breve in Relation to Salinity 

 and Temperature 



Over 400 fresh-water samples were col- 

 lected from Lake Okeechobee, Tanniami Canal, 

 and the Peace, Myakka, and Calosahatchee 

 Rivers. G^. breve was not found in these 

 samples. It was noted at river mouths only 

 during red-tide outbreaks in 1954 and 1957. 

 It occurred in low numbers from October 

 through December 1957 near the mouth of 

 the Manatee River at salinities ranging from 

 25. 37-29. 27%o. This occurrence coincided with 

 high concentrations of G. breve in the ad- 

 jacent neritic waters of area A (fig. 6). 



Most positive sannples occurred at salinities 

 from 31.0-34.9%o(table 2). Lethal concentra- 



tions (250,000/1.) were observed at salinities 

 ranging from 21,0-36,9%o. The lowest and 

 highest observed salinities for this flagel- 

 late were 21,2%o and 37.5%o. G, breve was 

 completely absent at salinities above 37,5%o. 

 The frequency distribution of G, breve at 

 observed water temperatures was determined 

 in 9,108 samples (table 2), G.. breve was noted 

 in the temperature range 10.3°-33,2° C. Most 

 blooms occurred from 14,0°-25.9° C, Lethal 

 concentrations were noted at 14.0°-31.9° C, 

 Most positive samples and lethal concentra- 

 tions occurred between 16, 0°- 17.9° C, 



Vertical Dispersion 



Using all paired surface and bottom samples 

 taken simultaneously during the 4- year period, 

 we found that G^. breve incidence was higher in 

 surface than in bottom samples (fig, 7). This 

 was generally true for the entire sampling 

 period and all areas. The majority of these 

 samples were taken during the daylight hours 

 between 0800 and 1700, 



DISCUSSION 



The distribution of G, breve during this study 

 extended from Anclote Key south to the Shark 

 River in the Florida Everglades, a range of 

 nearly 200 linear miles along the west coast 

 of Florida. The organisnn was not found in 

 Florida Bay or off the Florida Keys, Davis 

 (1948) reported G, breve during the 1946-47 

 red-tide outbreak in the waters off the Florida 

 Keys, Menzel stated that G^. breve was found 

 in Alligator Harbor about 130 miles northwest 

 of Anclote Key ^, Isolated blooms were ob- 

 served in the waters along the upper and lower 

 Texas coast and in the western Gulf of Mexico 

 (Wilson and Ray, 1956, and Collier, 1958). 

 G. breve also was reported from the coast of 

 Trinidad (Lackey, 1956), The distribution pat- 

 tern observed during this study and by other 

 investigations suggests that G_. breve is en- 

 demic to the Gulf of Mexico and the Caribbean, 



The frequent presence of G. breve in west 

 coast Florida waters indicates that it may be 

 considered a normal constituent of the resi- 

 dent phytoplankton population. Since its inci- 

 dence during nonbloom periods is primarily 

 confined to offshore waters, the organism prob- 

 ably is more neritic than estuarine (fig, 6). 

 G. breve occurred in approximately equal fre- 

 quency in both estuarine and neritic waters 

 only during the red-tide outbreaks in 1954 and 

 1957, The offshore distribution usually ex- 

 tended 6-10 miles, although in March 1960 a 

 bloom of 6,320,000/1, was detected 35 miles 

 offshore (Hutton, 1960), During the red-tide 

 outbreak of 1954, Lackey and Hynes (1955) 

 reported G, breve in samples collected 140 

 nniles southwest of Fort Myers, Fla, The 



'r. W. Menzel (personal communication, 1957), Florida 

 State University, Tallahassee, Fla. 



