3. Physical control by high-frequency 

 waves . Little attention has been paid to physi- 

 cal means of control. Lackey and Hynes (1955) 

 stated, ". . . It has already been shown, how- 

 ever, that there is no useful killing action in 

 a high-frequency radio field. . . ." 



4. Control by changing the pH. Galtsoff 

 (1948) wrote ". . . The use of powdered calcium 

 oxide (unslackened lime) suggests itself, for its 

 addition to sea water will raise the pH to a 

 level which is beyond the tolerance of the 

 dinoflagellate. . . ." [p. 35.] Wilson (1955) said 

 that G. breve grows best in pH of 7.3 to 8.1, 

 but survives pH from 7.0 to 8.6. Aldrich (1 959) 

 gave 7.5 to 8.3 as the pH range for good 

 growth of G. breve and said that a pH below 

 7.3 was definitely toxic. 



5. Control by adsorption of vitamins or 

 chelators or both . Adsorption of vitamins 

 required by G. breve through large-scale 

 dusting with charcoal was suggested by Odunn, 

 Lackey, Hynes, and Marshall (1955) as a 

 nneans of modifying offshore blooms. This 

 suggestion should be tested in the laboratory. 



6. Destruction of G. breve by nonselective 

 chemicals . The most widely tried method of 

 control for red tides has been the spreading 

 or dusting of water areas with nonselective 

 chemicals. The question of what destruction 

 these chemicals can do to organisms other 

 than the one in bloom is usually based on 

 general uneasiness, without substantial proof. 

 For instance, few question the spraying of 

 valuable estuarine nursery grounds withprac- 

 tically nondestructible hydrocarbons in the 

 name of mosquito control, yet many worry 

 about a very low concentration of copper 

 sulfate, which has only a momentary effect. 



Several nonselective chemicals have been 

 suggested for killing red-tide organisms di- 

 rectly: 



Ammonia was sharply inhibitory to growth 

 of Prymnesium parvum ; it was less toxic at 

 high salinity or at low pH (McLaughlin, 1958). 



Ferric chloride and chlorine gas were used 

 in Japan; materials were discharged over 

 the stern of a boat so they could be churned 

 into the water by the propeller (Anon., 1934). 



Calcium hypochlorite or liquid chlorine 

 was used by the Japanese either after or 

 with copper sulfate to prevent the growth of 

 bacteria after killing the dinoflagellates 

 (Galtsoff, 1948). 



Copper sulfate is the most widely used 

 chemical. The Japanese have used it for 

 many years to protect their oyster beds 

 from red tide. It was tried on a small scale 

 in Florida in 1952 by discharging a concen- 

 trated solution of 3,000 pounds of copper sul- 

 fate from the ballast tanks of the Alaska . In 

 1953 sacks of copper sulphate were towed fronn 

 small boats off Anna Maria Key. Later a small 

 area was dusted by plane. None of these ex- 

 periments was on a sufficiently large scale to 

 indicate the effectiveness of copper sulfate. 



In a large-scale experiment, during the 

 heavy outbreak of 1957, 105 tons of copper 

 sulfate were spread by crop-dusting planes 

 at about 20 pounds to the acre along 32 miles 

 of beach between Pass-a-Grille and Anclote 

 Keys (Rounsefell and Evans, 1958). 



7. Destruction of G. breve by selective 

 chemicals . The primary objective is to dis- 

 cover a chemical or chemicals toxic to G. breve 

 at low enough concentrations to hold promise 

 of being cheap enough to use for control, 

 that at the same time is specific for G. breve 

 or perhaps closely related species. The 

 screening of 4,306 compounds, including most 

 of those screened in past years in developing 

 a specific larvicide for the sea lamprey 

 ( Petromyzon marinus ) in the Great Lakes, 

 yielded 55 compounds toxic at 0,01 p. p.m. 

 (Marvin and Proctor, 1964). Further tests 

 (unpublished) have shown that several of these 

 highly toxic compounds do not harm several 

 other estuarine organisms. The laboratory 

 testing of these very toxic compounds, when 

 completed, should lead to pilot experiments 

 under field conditions. 



SUGGESTIONS FOR FUTURE RESEARCH 



In summarizing research to date on red 

 tide, we are immediately aware of the fact 

 that, despite some very significant progress, 

 many gaps remain in our knowledge. When 

 we consider the tremendous expenditures of 

 time and effort that have gone into the solu- 

 tion of many medical problems, such gaps 

 are not surprising. Serious red-tide research 

 is comparatively recent; barely 10 years have 

 elapsed since the first successful culturing 

 of the causative organism. Perhaps the chief 

 deterrent to progress has been the fluctuation 

 in financial support. Heaviest support has 

 followed severe outbreaks; support has de- 

 clined between outbreaks until, at times, the 

 level has become too low to provide ade- 

 quate continuity of field data. Despite the 

 marked improvement in the field programs 

 since the 1958 symposium finances have been 

 insufficient to keep up continuity in field and 

 laboratory and at the same time carry out 

 research on some of the imaginative sug- 

 gestions that were made. Perhaps some re- 

 orientation may aid in stretching the research 

 dollar. 



Several items suggested by the Advisory 

 Committee at the 1958 symposium have been 

 worked on, and some completed. These items 

 follow: 



1. Testing chemical comp oTindg to discover 

 one or more specific for G. breve . This work 

 has resulted in a report by Marvin 2uid Proc- 

 tor (1964) for 4,306 chemicals, several of 

 which show promise. This item should be 

 pushed vigorously. 



2. Does G. breve require a heterotrophic 

 existence? Aldrich (1962) showed that G. breve 



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