Distribution and Seasonal Occurrence of 

 Gymnodinium breve on the West Coast 

 of Florida, 1954-57 



by 



JOHN H. FINUCANE, Fishery Research Biologist 

 Bureau of Commercial Fisheries Biological Station 

 St, Petersburg Beach, Florida 



ABSTRACT 



The distribution and seasonal occurrence of Gymnodinium breve, the Florida 

 red-tide organism, was recorded for a 4-year period in estuarine and and neritic 

 waters along the Florida west coast. G. breve was found throughout the year in the 

 area from Tarpon Springs south to the Florida Everglades. Blooms of this dino- 

 flagellate occurred mainly from September through December in 1954 and 1957. 

 Essentially, both 1955 and 1956 were not red-tide years. The observed salinities, 

 temperatures, and distribution of G. breve are presented during both bloom and 

 nonbloom periods. 



INTRODUCTION 



This is the seventh report on field studies 

 of the red tide in Florida's coastal waters 

 by the Bureau of Commercial Fisheries. The 

 red-tide organism associated with mass mor- 

 talities of marine animals and discoloration of 

 water off the west coast of Florida was first 

 described by Davis (1948) as a new dino- 

 flagellate species, Gymnodinium brevis. Ray 

 and Wilson (1957) and Starr (1958) showed that 

 this organism produced a toxic substance(s) 

 lethal to fish. Hutton (1956) reviewed the 

 earlier red-tide literature covering the out- 

 breaks of 1946-47 and 1953-54. More recent 

 observations on the importance of dissolved 

 nutrients, salinity, and meteorological condi- 

 tions were reported by Collier (1958), Aldrich 

 and Wilson (1960), and Hutton (1960) respec- 

 tively. Chew (1961) noted the association of 

 red tides with hydrographic conditions off the 

 southwest Florida coast. Dragovich (1963) 

 reported on G. breve , other plankton, and 

 hydrology off Naples, Fla, 



Prior to our investigation of this red- 

 tide organism, little was known of its dis- 

 tribution. Our objective was to determine its 

 distribution and seasonal occurrence during 

 bloom and nonbloom years in an area ex- 

 tending from Tarpon Springs to the Florida 

 Keys. The effects of salinity and tempera- 

 ture on distribution of this organism were 

 also studied. 



MATERIALS AND METHODS 



The sampling areas and station locations 

 are shown in figures 1-5. At the beginning 

 of the red-tide research program in February 

 1954, sampling was confined mainly to areas 

 of fish kills, and no stations were occupied 

 south of Cape Romano. Systematic biweekly 

 or monthly sampling of the entire area of 

 investigation was begun in 1955 and continued 

 through 1957. Most sannpling was confined to 

 bay and offshore waters. Fresh-water canals. 

 Lake Okeechobee, and the upper reaches of the 

 Caloosahatchee and Peace Rivers also were 

 sampled (figs. 2-5). In this report, all passes, 

 bays, sounds, and river mouths were ternned 

 estuarine waters, Neritic waters included all 

 adjacent coastal areas in the open Gulf. All 

 offshore sampling stations were in the latter 

 category, and the majority of them were lo- 

 cated within the 10-fathom (fm.) contour 

 (figs. 2-5). Half of the stations were between 

 sea surface and 2 fm. in areas A through D, 

 Numbers of G^, breve , enumeration techniques, 

 sampling nnethods, and associated oceano- 

 graphic data were previously reported by 

 Finucane and Dragovich (1959) and Dragovich, 

 Finucane, and May (1961), 



The term "bloom" represents any concen- 

 tration of G, breve exceeding the normal popu- 

 lation level of approximately 1 ,000/1 ,G, breve 

 counts of more than 250,000/1 , were considered 

 lethal during red-tide fish kills. 



