Field Studies of Red Tide 



Since 1954 the Bureau of Commercial Fish- 

 eries has gathered environmental data that 

 included concurrent enumerations of G. breve . 

 One of the chief aims when this sampling 

 began was to attempt to predict red-tide 

 outbreaks by noting the gradual increase in 

 abundance of the orgEinisms. Unfortunately, 

 high concentrations of the organism appear 

 with little prior warning. In 1957 this pro- 

 gram was revised to give nnuch more in- 

 tensive coverage of one area- -Tampa Bay 

 and vicinity. More chemical determinations 

 were also added. 



One of the first tasks should be to complete 

 the analysis of this accumulation of environ- 

 mental data. It is inriportauit to know which 

 factors can safely be dropped, which must be 

 retained, and how much sampling is needed 

 for a reliable estimate of population changes. 

 In the analysis of these data we feel it im- 

 portant to obtain detailed data on wind direc- 

 tion and velocity. If convergences play as 

 important a role as is strongly suspected in 

 the rapid concentration of organisms, and 

 possibly equally innportant, in permitting the 

 organisms to grow in low-nutrient water, 

 then winds may be one of the major factors 

 in overblooming. Any modifications of the 

 present sampling program should await the 

 results of the analysis of the accumulated 

 data to prevent discontinuity of the records. 



A detailed hydrographic survey of the areas 

 adjacent to the nnouths of the principal passes 

 should be made under varying conditions of 

 tide, wind, and residual outflow of brackish 

 water. This survey should include an attempt 

 to locate the position of convergences amd 

 the speed of the vertical currents. Once this 

 detailed information is available for a major 

 pass we suggest a model study to determine 

 whether it is feasible to make smy modifica- 

 tions of the pass (such as underwater barriers 

 to restrict mixing, jetties, etc.) to aid in two 

 objectives: 1) to lessen the formation of 

 convergences and 2) to prevent the formation 

 of large bodies of nnixed Gulf and bay waters 

 of salinities favorable for G_. breve. 



One importamt aspect of the field work 

 that may need nnore emphasis is obtaining 

 reliable quamtitative data on the relative 

 abundance, both seasonally and annually, of 

 other plankters. G. breve cam grow in water 

 of relatively high salinity but appears to 

 bloom more often in the fall, usually at lower 

 salinities.-suggesting that the stimulation of 

 growth depends upon some terrigenous sub- 

 stance brought into the Gulf by the rivers, 

 or upon previous chauiges in the neritic waters 

 dependent upon other plankters, or both. The 

 influence of the previous plankton population 

 could operate in at least three ways: l)through 

 rennoval of some substance inhibitory to 

 G. breve , 2) by excretion of a substance 



favorable to G. breve , or 3) by providing 

 competition, perhaps through excretion of a 

 substance detrimental to G. breve . 



These quantitative data on other plankters, 

 thus, need to be supplemented by laboratory 

 work on the effect of these plankters, or of 

 the water in which they have grown, on the 

 growth of G. breve . It nnay be necessary to 

 grow cultures of a number of plankters. 

 These cultures should include forms that 

 prey directly upon G. breve . If predatory 

 forms could be encouraged by any feasible 

 means, this type of control would be pref- 

 erable to the use of nonspecific algicides. 



At the meeting of the Advisory Committee 

 at the 1958 symposium (USFWS, 1958) Rice 

 suggested that field observations be made in 

 an area outside the areas in which red-tide 

 outbreaks normally occur. Comparison of 

 chemical, physical, and biological data from 

 the two areas might serve to isolate one or 

 more causative factors. 



Control Methods 



Control methods have been discussed at 

 some length in the section "Control of out- 

 breaks." Here we discuss only new or un- 

 tried methods. 



The chief deterrent to the use of non- 

 specific algicides is the possibility of 

 inflicting serious damage to other forms. 

 If applied carefully in concentrations just 

 high enough to kill G. breve , this damage 

 will be chiefly to plankton, including larval 

 forms. Since dinoflagellates tend to concen- 

 trate in convergences because of their ability 

 to resist vertical currents, it might be feasible 

 to control the red-tide organisms by treat- 

 ment of the convergences only and, thus, 

 inflict minimal damage to other forms. This 

 end might be accomplished by gradually dif- 

 fusing the algicide from floating material, 

 such as coarse sawdust. 



Algae in fresh water lakes have been suc- 

 cessfully controlled by the use of aniline dye 

 (Eicher, 1947). In a 200-acre lake averaging 

 10 feet deep, nigrosine dye was applied at 

 10 pounds per acre. The water became black, 

 and 18 months later retained about 50 percent 

 of its dark color. One very noticeable effect 

 was the lowering of the pH. Whether it is 

 feasible to shield the light by use of dye- 

 stuffs, or perhaps sonne cheaper material, 

 sufficiently to affect G. breve significantly 

 should be investigated. 



Need for Coordinated Research 



It has become abundantly clear that research 

 on red tide involves several disciplines-- 

 both physical and biological oceanography, 

 microbiology, ainalytical chemistry, bio- 

 chemistry, aind mathematics; several types 

 of physical equipment and infinite patience also 



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