Table 2. — Seasonal occurrence of Florida red tides 



^ Underlining indicates initial month of an outbreak; dashes join portions of same outbreak 

 during temporary recession. 



To accomplish this concentration, either the 

 organism must travel through the water col- 

 unnn, or the water column must move past 

 the organism. 



2. The occurrence of blooms in streaks with 

 abrupt margins suggests that the organisms 

 are concentrated by one or all of three means: 



a. Convergences paralleling the shore, 

 set up by gentle onshore winds. 



b. Convection cells parallel to steady 

 winds, causing parallel streaks. 



c. Convergences at the mouths of passes, 

 where the residual outward flow of less saline 

 water near the surface meets the more saline 

 Gulf water. 



3. The repetition of Outbreeiks adjacent to 

 the mouths of passes where convergences would 

 occur most frequently and consistently. 



4. The fact that (unlike diatoms) dinoflag- 

 ellates can resist vertical currents. Peters 

 (1929) suggested that some species can sue - 

 cessfxilly oppose a vertical current of about 

 1 cm. per second; he said that Ceratiunn can 

 move through 5 to 10 m. in 12 hours or less. 

 Pomeroy et al. (1956) found that Gymnodinium 

 sp. would seek a light source at 0.3 to 0.8 

 cm. per second. 



5. The sudden appearances of fish-killing 

 concentrations of G. breve in areas in which 

 continuous sannpling showed densities far too 

 low to reach the high concentrations found, 

 in the allotted time, if the increase were 

 based on division rates. Thus, Finucane 

 (USFWS, 1958), speaking of the beginning of 



the 1957 outbreak, said, "The population did 

 not build up rapidly at the time of the last 

 outbresik, only to 12,500 per liter a day and 

 a half before fish kills started." On the ques- 

 tion of division rates Wilson (USFWS, 1958) 

 stated, "It fluctuates, the average rate of a 

 division is 0.4 per day for a particular day 

 but not over a longer period." Lackey and 

 Hynes (1955) stated that under optimum con- 

 ditions several divisions may occur in 24 

 hours. Collier (1955) wrote that the addition 

 of juices from freshly killed fish caused an 

 "explosive bloom" which tripled the number 

 overnight. Wilson (1955), however, using the 

 same mecins, found it took 4 days to triple 

 the numbers in the culture. 



6. Strong winds usucilly break up fish- 

 killing concentrations suggesting that winds 

 of much velocity cause stronger downward 

 vertical currents than can be opposed by the 

 organisms and cause them to become dis- 

 persed through the water in concentrations 

 below the lethal level. Wilson (USFWS, 1958) 

 stated that, ". . . Strong offshore winds, roughly 

 above 18 mph, will probably be detri- 

 mentcil to a bloom developing but calm to 

 moderate onshore wind will probably be bene- 

 ficial." 



7. When severe outbreaks are dispersed 

 by strong winds, apparently enough orgauiisms 

 remain to cause outbreeiks to recur quickly 

 when the wind moderates. Such sudden re- 

 currences imply the existence of a concen- 

 trating mechanism. 



