If the operation is to be successful, there 

 are other requisites which are often disre- 

 garded, i.e., freedom from administration, a 

 high degree of initiative and competence, and 

 wide cooperation with researchers here and 

 abroad. It is highly advisable that a great deal 

 of the hydrological work be cotitracted to other 

 laboratories, as mentioned before. The labo- 

 ratory work on bacteria -free cultures --an area 

 where there are few competent workers--can 

 be done anywhere (be it in the United States, 

 Canada, England, Germany). Specialists canbe 

 induced to cooperate. 



The essential work to be done in situ is 

 hydrography, chemistry, taxonomy, and the 

 collection of samples. It is also necessaryand 

 easier to establish raw and clonal cultures of 

 the various dominant organisms of the Gulf in 

 situ. Bacteria-free cultures can be achieved 

 anywhere, but the physiological work should be 

 done exclusively on the strains isolated in the 

 Gulf, even if the same species are already in 

 bacteria-free culture elsewhere. We know that 

 strains of the same species from different 

 localities have widely different nutritional re- 

 quirements. 



The existing body of knowledge on red tides 

 should be extended widely, as has been men- 

 tioned by other participants in this Symposium. 

 We need to know far more about the hydrology 

 of the region and the physical and chemical 

 influence of the rivers. These rivers, rich in 

 tannic and humic acids (bothmetal-chelators), 

 are sure to enrich the coastal waters with 

 metals. The cycle of iron is being investigated 

 but is still poorly known. The cycle of other 

 trace metals--z,inc, copper, cobalt, molyb- 

 denunn, manganese, titanium, zirconium, and 

 others--which may be necessary, stimulatory, 

 or poisonous to algae is completely unknown. 

 A study of the concentrations of trace metals, 

 vitamins, and other nutrients in the water is 

 essential; so is the study of their role in the 

 nutrition of the different species of algae of 

 the Gulf, including G. breve , which is already 

 in bacteria-free culture. 



Plant hormones and unknowns should not be 

 excluded. We have found that normal mor- 

 phology of two green seaweeds, lost when they 

 are grown aseptically, can be restored by 

 adding filtrates of two marine bacteria, or by 

 supernatants of aseptic cultures of red or 

 brown seaweeds. The active principle of the 

 supernatant of brown seaweeds, extracted by 

 charcoal and eluted by ethanol, is a tannin. 

 Higher plant tannins, and the waters of the 

 Florida rivers investigated, have no effect on 

 the two green seaweeds, but they may contain 

 some active substances for the local phyto- 

 plankton or G. breve . Similarly, the chennicals 

 produced by a preceding bloom during life or 

 after decay, can deternnine by their inhibitory 

 or beneficial action which one of the nnany 

 species is to grow to bloom proportions next. 

 A host of exciting mysteries awaits the anxious 



hand of the researcher who will persist until 

 he uncovers them. 



Last but not least, after the first broad 

 analysis of the environment it would be waste- 

 ful to continue working throughout a region as 

 vast as the one in which the red tides occur. 

 The concerted Woods Hole approach, which is 

 a work in depth where every detail counts, 

 should be accomplished at a snnall number of 

 stations carefully selected to be representative 

 of the environment being studied. As one 

 environmental niche becomes well known, the 

 next niche should be taken up and analyzed. 



SCREENING OF CHEMICALS FOR THE 

 CONTROL OF GYMNODINIUM BREVE 



By Kenneth T. Marvin 



Bureau of Commercial Fisheries Biological 

 Laboratory, Galveston, Tex. 



The Bureau of Commercial Fisheries has 

 been investigating the chemical control of red 

 tide for about 12 years. Most of the initial in- 

 vestigation centered around the use of copper. 

 The conclusion from field testing was that 

 copper sulphate gave some temporary relief 

 in localized areas, but that effects were not 

 durable enough to be considered economically 

 feasible for a large-scale application. 



Since March 1959, some 4,700 primarily 

 organic compounds have been screened sys- 

 tematically as possible control chemicals. A 

 material was considered acutely toxic to 

 G. breve if it produced 100 percent mor- 

 tality within a 24-hour period at a concentra- 

 tion level of 0.04 p. p.m. Culture media were 

 based on water taken several miles offshore 

 at St. Petersburg Beach, Fla. G. breve used 

 in the tests had been maintained under labo- 

 ratory conditions about 6 years. Of the com- 

 pounds tested, 191 were acutely toxic. The 

 second phase consisted of determining the 

 minimum toxic levels of the compounds in 

 artificial media and then running tests to 

 determine how many, if any, were selective 

 enough to be considered as controls for 

 G^. breve . Four compounds were toxic at 0.0004 

 p. p.m., 5 at 0.001 p.p.nn., 20 at 0.004 p.p.m., 

 32 at 0.01 p.p.m., and 120 at 0.04 p.p.m. 



At this point, it was decided that a potential 

 control must produce 100 percent mortality to 

 G. breve within 24 hours at a level of 0.01 

 p.p.m. This standard left 32 compounds with 

 which to conduct selectivity tests. Estimates 

 of the specificity of the "0.01 compounds" were 

 obtained by testing them against commercially 

 important indicator organisnns, such as post- 

 larval shrimp, small fish and crabs, and other 

 forms of marine animal life from the Gal- 

 veston, Tex., area. The selectivity require- 

 ment arbitrarily assigned to a potential control 

 was that it must not kill nnore than 50 percent 



