8. Despite strong tidal movements through 

 the passes, and a general residual current 

 flowing northward along the coast, a fish- 

 killing concentration may remain in virtually 

 the same place over several days at a time. 

 This persistence could be explained by the 

 organisms being held in one area by a con- 

 vergence at the mouth of the pass. Wilson 

 (USFWS, 1958), in discussing an early con- 

 trol experiment, said, ". . .this bloom had 

 persisted in this area [0.2 square mile] for 

 22 days." He also stated, "If you find a high 

 concentration of organisms one day, it tends 

 to be at this location the next day. If there is 

 water movennent you would expect to find them 

 at some other location and not at approxi- 

 mately the same position day after day." 



There is some evidence that dinoflagellates 

 tend to sink toward the bottom at night and 

 rise to the surface during the day. The 

 sinking may not be purposeful movement, 

 but merely a tendency for the organisms 

 to become dispersed at night when there is 

 no light to bring them toward the surface. 

 Pomeroy et al. (1956) mentioned that they 

 observed a bloom of Gymnodinium sp. that for 

 4 successive days disappeared at night and 

 in the early nnorning and reappeared each 

 day at about 9 a.m. While spraying copper 

 sulphate during the control experiment in 

 the heavy outbreak of 1957, it was noted 

 that concentrations of G. breve were not 

 apparent in the early morning before the sun 

 attained a high angle. 



Because dinoflagellates cam move vertically 

 they may be able in calm weather when con- 

 vergences are fewer to strain the nutrients 

 from a goodly part of the water column. 



That a dense concentration of organisnns is 

 usually formed either at a convergence or in 

 very calm water is shown by the fact that 

 concentrations of G. breve often occur in 

 places protected from currents, such as small 

 bays, or the stagnant fingers made by dredging 

 narrow blind channels to make waterfront 

 lots (Ingle et al., 1959). Wilson (USFWS, 

 1958) said, "You normally have more plankton 

 bloom and red tide during periods of calm 

 weather." 



never very abundant from March through 

 August. For the 3-month period from Sep- 

 tember through November, the contour lines 

 of relative abundance are shown in figures 

 5 and 6. Centers of high abundance were in 

 the Sanibel Island area and adjacent to the 

 mouth of Tampa Bay. Heavy concentrations 

 tended to hug the coastline. A light concen- 

 tration extending seaward off Tampa Bay may 

 be a reflection of the permanent counter- 

 clockwise eddy which, according to Hela, de 

 Sylva, and Carpenter (1955), seems to have 

 its northern end at the latitude of Tampa Bay. 

 During 2 months (December-January) the 

 distribution was in general similar (figs. 7 

 and 8), but the level of abundance had fallen 

 in the north, which may well reflect the 

 curbing effect of cooler water. 



Pollution as a Contribution to Red-Tide 

 Outbreaks 



The question has been raised as to whether 

 nutrient-rich pollution, especially domestic 

 sewage, contributes in initiating or main- 

 taining outbreaks of red tide. Odum (1953) 

 found in Florida that 18 small unpolluted 

 streams contained 0.019 p. p.m. (parts per 

 million) of phosphorus, 10 small acid streams 

 draining phosphatic formations contained 0.413 

 p. p.m., and 7 streams not draining phosphatic 

 formations but receiving sewage contained 

 0.836 p. p.m. The effects of sewage could 

 result from an increase in phosphorus and 

 nitrogen or from some other condition. Bac- 

 teria working on sewage, for instance, might 

 increase the amount of VitaminBi2 available. 

 Wilson (USFWS, 1958) said ". . . possibly the 

 most important aspect of stream discharges 

 which are contributing to red tides is that 

 some form of chelating agent may be in this 

 water. . . ." 



If red tides are tending to occur more 

 frequently, and especially if they are tending 

 to occur more toward the northern portion 

 of the red tide area, one might well suspect 

 that pollution from the mushrooming cities 

 around Tampa Bay is contributing to their 

 occurrence. 



Coastwise and Seasonal Abundance 



One of the first steps in analyzing the 

 1954-60 raw data on G. breve was to deter- 

 mine how the organisms were distributed 

 both seasonally and in relation to the coast. 

 For this purpose the data were coded into 

 10 north-to-south areas, each measuring 25 

 miles along the general trend of the coast 

 (fig. 1). To obtain the distribution in relation 

 to the land, the data were also coded in 

 bands of distance offshore, and, for stations 

 inside the fringing barrier islands, by dis- 

 tance to the mouth of the nearest pass. It 

 was obvious that in 1954-60 organisms were 



LIFE FORMS OF GYMNODINIUM BREVE 



Very little has been published on life forms 

 of G^. breve . Detailed descriptions of the 

 organism appear in Davis (1948) and Lackey 

 and Hynes (1955). The latter stated that the 

 only observed method of reproduction is by 

 binary fission. Wilson (USFWS, 1958) men- 

 tioned observations on cysts. He stated that 

 he could not make G. breve encyst by tem- 

 perature adjustments. When questioned con- 

 cerning whether cysts would divide, he stated, 

 "I have put in from one to 20 in sterile media 

 and found that they will encyst and divide." He 



10 



