Methods of Control 



Methods of control of red tide depend 

 largely on whether the objective is preven- 

 tion, control, or nnere alleviation. 



Under alleviation fall such measures as 

 seining of dead fish to keep them off the 

 beaches; also, the common practice of using 

 bulldozers and other power equipment to bury 

 mechanically, or to gather together amd re- 

 nnove, the dead fish washed or blown ashore. 

 At best these are temporizing measures. As 

 we have noted previously, fish-killing con- 

 centrations of red tide tend to remain close 

 to shore, sometimes inside the passes. These 

 temporizing measures do not help against 

 the irritating aerosols, nor can they keep 

 all fish off the beaches when the concentra- 

 tions innpinge so closely on the fringing 

 islands. Numerous suggestions have been made 

 for both prevention and control, each of which 

 we discuss in turn. 



Prevention of Outbreaks 



Prevention of outbreaks before they get 

 started involves alteration of the habitat either 

 chemically or physically. 



1. Inhibiting the growth of G. breve by 

 raising and nnaintaining the concentration of 

 heavy metals at an inhibitory level . The idea 

 here was to raise the level of copper (or 

 other heavy metal) in the inshore waters 

 sufficiently high to inhibit the growth of the 

 red-tide organism without actually destroying 

 it. Should an outbreak nevertheless occur, 

 only minimal amounts of copper added to 

 the water should suffice to kill G. breve 

 because of the existing high level of copper. 

 The feasibility of this idea was tested by 

 using copper ore, and the method was re- 

 jected (see Marvin 1958, 1959; Marvin, Lans- 

 ford, and Wheeler, 196l). 



2. Keeping the nutrient level low by curbing 

 use of streams zmd bays for disposal of 

 nutrient-rich sewage or other pollutants . Since 

 G. breve Ccui apparently thrive in nutrient- 

 poor water, this suggestion does not appear 

 too promising. We do need to know whether 

 sewage pollution contributes other substances 

 needed by the organism. 



3. Controlling river flows in streams for 

 which water can be stored so as not to create 

 ideal conditions for blooming . Some streanns, 

 particularly the Caloosahatchee River, have 

 enormous storage capacity. By regulation of 

 the flow (a detailed hydrographic study at all 

 flow levels is highly desirable) it may be 

 possible to prevent the formation of water 

 of suitable salinity in a zone of strong con- 

 vergences. Seasonal releases of blocks of 

 water, either to get rid of surplus water 

 during a period when conditions appear un- 



suitable for blooms, or to suddenly lower 

 the inshore salinity below tolerable levels 

 for G. breve should be considered. One might 

 speculate as to whether the former larger 

 flows of fresh water southward through the 

 Everglades had any effect on earlier red 

 tides, which seem to have been more southerly 

 in occurrence. 



4. Encouragement of competing or inhibi- 

 tory organisms by special types of fertiliza- 

 tion . This idea appears to be innplicit in the 

 suggestion of the University of Miami Marine 

 Laboratory (1954) that the carrying out of 

 extensive fish culture in the back bays might 

 cause changes in the habitat detrimental to 

 G. breve . The danger here lies in losing the 

 estuarine nursery areas needed by shrimp 

 and various sport and commercial fishes. 



5. Altering the physical habitat through con- 

 struction of underwater barriers, jetties, or 

 similar structures at passes to restrict mixing 

 of Gulf cind bay waters, and perhaps to change 

 the pattern of the convergences at the mouths 

 of the passes . This suggestion (which we 

 have slightly elaborated) was made by Robert 

 Hutton at the meeting of the Advisory Com- 

 mittee at the 1958 symposium (USFWS, 1958). 

 It certainly deserves full attention. 



Control of Outbreaks 



Only a few of either the preventive meas- 

 ures listed above or the control measures 

 discussed below have been tried, even on a 

 laboratory scale. Nevertheless, at the present 

 state of our knowledge, we cannot afford to 

 dismiss or reject ideas in cavalier fashion. 

 Sonne of the untried suggestions undoubtedly 

 have merit- -it is a question of patient re- 

 search, pilot experiments, and economics. 



1. Biological control through the use of 

 bacteria . The use of bacteria to destroy the 

 toxin of the red tide was suggested at the 

 1958 symposium (USFWS, 1958). The use of 

 bacteria that destroy vitamin Bj2 was sug- 

 gested by Hutner and McLaughlin (1958), but 

 dismissed with the comment that "truly 

 enormous quantities of bacteria would be 

 required. . . ." 



2. Biological control through encourage- 

 ment of predator organisms . The encourage- 

 ment of predator organisms was mentioned 

 by several authors. Galtsoff (1948) mentioned 

 the ingestion of G^. breve by a cladoceraui, 

 Evadne. Hutner and McLaughlin (1958) men- 

 tioned the ciliate protozoans amd the luminous 

 dinoflagellate, Noctiluca. Torrey (1902) men- 

 tioned the appearance of Noctiluca in great 

 nun-ibers toward the end of July amd their 

 devouring Gonyaulax "with avidity." There 

 is no comnnent on how to encourage these 

 predators, short of providing them a red- 

 tide bloonn. 



13 



