LABORATORY EVALUATION OF RED-TIDE CONTROL AGENTS 



By Kenneth T. Marvin and Raphael R. Proctor, Jr., Chemists 

 Bureau of Commercial Fisheries Biological Laboratory, Galveston, Texas 77550 



Intense blooms of the dinoflagellate Gymnodinium 

 breve Davis that occur at irregular intervals along 

 the west coast of Florida (Feinstein, Ceurvels, 

 Hutton, and Snoek, 1955) may cause extensive mor- 

 tality of marine organisms. The blooms are popu- 

 larly knowTi as red tides because of the amber to red 

 discoloration they impart to the water. 



The Fish and Wildlife Service initiated studies in 

 1948 to determine the possibility of artificial means 

 to reduce the occurrence or intensity, or both, of the 

 red tides. Early tests indicated that copper, in con- 

 centrations as low as 0.03 p. p.m., is lethal to labora- 

 tory cultures of the red-tide organism. Rounsefell 

 and Evans (1958), and Alarvin, Lansford, and 

 Wheeler (1961) demonstrated, however, that control 

 by copper was not feasible under field conditions. 

 The copper precipitated from solution after a few 

 days and, consequently, was ineffective for control. 

 In 1959, scientists of the Bureau of Commercial 

 Fisheries Biological Laboratory in Galveston, Te.\-., 

 began a systematic evaluation of 4,30G compounds 



'Contribution No. 215, Bureau of Commercial Fisheries Biological 

 Laboratory. Galveston, Tex. 

 Note. — .\pproved for publication May 6. 1966. 



as red-tide to.xicants. The initial phase of the study 

 (Marvin and Proctor, 1964) involved testing each 

 compound to determine its toxicity to G. breve. The 

 final phase of the study, described here, evaluated 

 some of the more toxic materials in the laboratory. 

 We investigated only the compounds that we deter- 

 mined to be 100-percent lethal to G. breve within 24 

 hours at concentrations of 0.01 p. p.m. or less. A 

 red-tide control agent must also be selectively toxic; 

 it must kill the red-tide organism without harming 

 other species. 



The chemicals fulfilling the toxic requirement for 

 red-tide control were tested for selectivity by deter- 

 mining their effects on juvenile forms of marine 

 species living in Galveston Bay and adjacent coastal 

 waters. The selectivity threshold concentration was 

 set arbitrarily at 0.1 p.p.m. Chemicals that killed 

 50 percent or more of any test organism within 24 

 hours at or below this concentration were rejected. 

 The five chemicals that passed the selectivity tests, 

 their effects on the test organisms at the threshold 

 concentration, and the species tested are noted in 

 table 1. 



T.\BLE l.—Pcrce>itage mortality of test organisms held 24 hours at toxicant concentration levels of 0.10 p.p., 



Chemical 



Carbamic acid, diethyldithio-; tellurium salt... 

 Carbamic acid, dimethyldithio-: ferric salt 



Disulfide, bis(diethylthiocarbamvl) 



Sulfide, bis(2-hydrosy-3-bromo-5-chlorophenyi)-; 



bi.s dimethylamino butyne monosalt 



Sulfide, bis(2-hydro.\y-.3-bromo-5-chlorophenyl)-; 



cyclohexylamine mono salt 



Species' 



Blue 



crab 



(megalops) 



striped 

 mullet 



Brown 



shrimp 



(postlarval) 



Sailfln 

 molly 



Marsh 

 periwinkle 



Shccpshead 

 minnow 



Hermit 

 crab 



Atlantic 

 croaker 











20 







10 



^SSSEf------ --^^ 



FISHERY bulletin: VOL. 66, NO. 1 



163 



