absence of extensive blooms of G. breve 

 reported here is probably attributable to fac- 

 tors other than unfavorable temperature. 



RELATION OF SALINITY TO OCCURRENCE 

 OF GYMNODINIUM BREVE 



Laboratory and field studies have been made 

 also on the effect of salinity on G. breve . In 

 bacteria-free cultures, Aldrich and Wilson 

 (i960) observed good growth within the salinity 

 range 27 p.p.t. through 37 p.p.t., and poor 

 growth at values lower than 24 p.p.t. or higher 

 than 44 p.p.t. In media with a salinity of 

 13.7 p.p.t. or less, no live cells of G. breve 

 were detected 1 day after innoculation. Field 

 data on occurrence of G. breve at various 

 salinities vary (table 3), and agree only par- 

 tially with the laboratory observations by 

 Aldrich and Wilson (I960). The most favorable 

 salinity range for growth of G. breve under 

 natural conditions probably is between 21 and 

 37 p.p.t. (Finucane, 1964). According to 

 Rounsefell and Nelson ( 1 964), the upper salinity 

 limit for good growth appears to vary with 

 temperature, and salinity becomes linniting at 

 37 p.p.t. when temperature exceeds 23° C. 



In our study G. breve occurred at salinities 

 from 33.68 to 37.01 p.p.t. The majority of 

 samples containing the organism were from 

 water of salinity of 35.0 and 36.9 p.p.t. 

 (table 3). Highest counts were during periods 

 of reduced salinity (February and September- - 

 see figs. 2a and 2c). G. breve occurred only 

 once in samples with salinity above 37.00 p.p.t., 

 and in samples with salinity below 33.0 none 

 were found. 



The salinities at which G. breve occurred 

 in our study fell within the range at which 

 Aldrich and Wilson ( 1 960 ) obtained good growth 

 under laboratory conditions. Furthermore, on 



the basis of salinities observed by others 

 (table 4), conditions in the area of investigation 

 were favorable for blooms of G. breve even 

 though no outbreak appeared. Thus our obser- 

 vations support the view that favorable salinity 

 alone may not be the major factor in the 

 proliferation of G. breve (Aldrich and Wilson, 

 1960; Dragovich, 1963; Finucane, 1964). 



THE ROLE OF LAND NUTRIENTS AND 



PRECIPITATION IN THE DISTRIBUTION 



OF GYMNODINIUM BREVE 



Nutrients from land drainage play an im- 

 portant role in outbursts of phytoplankton 

 (Wilson and Collier, 1955; Lucas, 1955; Wilson, 

 1951; Numann, 1957). A reduction in salinity 

 in coastal waters is usually the first condition 

 associated with periods of rainfall and in- 

 creased land drainage. Offshore salinity was 

 above 35.00 p.p.t. in 80.1 percent of the obser- 

 vations during the period of study; thus the 

 offshore environment was essentially marine 

 most of the time. Consequently, additions of 

 nutrients via land drainage may have been 

 insufficient to produce conditions required for 

 lethal red-tide blooms. 



On the basis of the incidence and counts of 

 G. breve , the favorable conditions for its 

 proliferation fell during February, March, 

 and September 1964, the months of heavy 

 rainfall and reduced salinity. Wilson in a 

 simultaneous and independent investigation 

 tested the suitability of waters from the study 

 area for growth of G. breve in unialgal cul- 

 tures (personal communication). ^ He found 

 that the water was most suitable for growth 

 of the organism in February, March, August, 

 September, and October 1964. 



Table <4. — Salinity ranges within which 

 Gymnodinium breve was reported under 

 field conditions 



COMPARISON OF DISTRIBUTION OF 



GYMNODINIUM BREVE IN 1964-65 WITH 



THAT PREVIOUSLY REPORTED 



The seasonal, spatial, and vertical distri- 

 bution of G. breve was essentially the same 

 as observed during other non-red-tide years 

 off the coast of west Florida (Finucane, 1964; 

 Rounsefell and Nelson, 1964). Usually the 

 organism was absent in bays but present in 

 neritic areas. Our observation that G. breve 

 is a relatively stenohaline organism which, 

 during a non-red-tide year, occurs in low 

 concentrations in the neritic waters of west 

 Florida is in agreement with the findings of 

 Finucane (1964), Aldrich and Wilson (I960), 

 Dragovich (1963), and Rounsefell and Nelson 

 (1964). 



Wilson, William B., Florida State University, Talla- 

 hassee, Fla. 



14 



