Distribution and Occurrence of Gymnodinium breve 

 on the West Coast of Florida, 1964-65^ 



By 



ALEXANDER DRAGOVICH and JOHN A. KELLY, JR., Fishery Biologists 



Bureau of Commercial Fisheries Biological Laboratory 

 St. Petersburg Beach, Fla. 33706 



ABSTRACT 



The distribution and monthly occurrence of Gymnodinium breve , the Florida 

 red-tide organism, were determined over a period of 13 months (in 1964-65) in the 

 coastal waters of west Florida. Counts of G. breve varied from to 53,800 cells 

 per liter of water; no fish kills were observed. The organism was present at all 

 stations from 9.3 km. (5 miles) to 37.1 km. (20 miles) offshore. It was not present 

 in samples from Tampa Bay, and it was found only twice in samples from Charlotte 

 Harbor. The highest occurrence of G. breve was in samples taken 27.8 km. (15 miles) 

 offshore. Vertical distribution of the species was greatest at the surface and at 5 m. 

 and lowest at 20 m. The largest concentrations of G. breve occurred in September 

 during a period of reduced salinity and temperature. Because these two factors are 

 innportant to the ecology of the organism, their relation to the presence or absence 

 of G. breve is discussed. G. breve were found within the tennperature range 13.8° to 

 30.6° C. It was absent or rare at both the low and high temperatures; cell densities 

 greater than 1,000 per liter were observed from 26.0° to 27.9° C. The organism 

 occurred at salinities ranging from 33.68 to 37.07 p.p.t. The highest concentration 

 of cells and incidence was noted within the salinity range 35.00 to 36.90 p.p.t. 



INTRODUCTION 



Gymnodinium breve Davis is the nonthecate 

 dinoflagellate that causes red tide inestuarine 

 and neritic waters along the west coast of 

 Florida. Dense concentrations of the organism 

 discolor the water and produce toxic metabo- 

 lites that cause catastrophic mortality among 

 fishes and other marine animals. References 

 to previous reports on the distribution and 

 seasonal occurrence of G. breve were pre- 

 sented by Finucane (1964). Rounsefell and 

 Nelson (1966) reviewed published and un- 

 published papers and data on red tide, and 

 Rounsefell and Dragovich (1966) examined 

 the relation between oceanographic factors 

 and abundance of the Florida red-tide or- 

 ganism. At the Red- Tide Symposium held in 

 October 1964 at St. Petersburg Beach, Fla., 

 past and current red-tide research was ex- 

 amined and several suggestions for future 

 studies were presented (Sykes, 1965). 



1 Contribution No. 30, Bureau of Commercial Fisheries 

 Biological Laboratory, St. Petersburg Beach, Fla. 



This study presents information on the 

 seasonal occurrence and distribution of G. 

 breve in an area of recurrent red-tide out- 

 breaks covering about 2,800 sq. km. (1,600 

 square miles) along the west coast of Florida. 

 Systematic monthly collections of such mag- 

 nitude to monitor G. breve and observe 

 oceanographic conditions have not been made 

 previously in the region. Our work made it 

 possible to corroborate and extend information 

 on several aspects of the ecology of G. breve 

 in Florida waters. 



SAMPLING METHODS AND LABORATORY 

 TECHNIQUES 



From February 1 964 through February 1 965, 

 water samples were collected monthly to de- 

 termine the abundance of G. breve and to 

 measure water temperature and salinity. We 

 established 22 stations in Tampa Bay, Char- 

 lotte Harbor, and at regular intervals along a 

 series of transects extending 37.1 km. (20 

 miles) offshore (fig. 1). The water column was 

 sampled during daylight at 5-m. intervals 



