also stated, ". . . Cysts form chains and when culture is stirred these tend to remain together, but I have never seen a chain formation of normal free swimming cells." There are several statements that G. breve affects the viscosity of the water when numerous. Galtsoff (1948) stated, ". . . the water had an oily appearance. When dipped up and allowed to stand for 5 to 10 minutes, it became thick, sometimes almost of a consistency of Karo syrup, and slimy to the touch...." Gunter, Smith, and Williams (1947) reported, "The water was viscid and slimy, having the consistency of diluted syrup." Collier (USFWS, 1958) said, '... observing with a dissecting microscope, the viscosity seemed to be caused by the organisms agglutinating. While I watched they started joining in long chains, long branching chains. . . .' There may be another answer to the high viscosity. Martin and Nelson (1929) found by killing Gymnodinium sp. with special solutions that they could observe a gelatinous envelope as thick as the diameter of the cell itself. They stated, "Gelatinous envelopes are common among dinoflagellates when encysted, but not when active. The cells referred to in this connection were actively motile. A similar envelope has been noted occasionally surrounding other species of naked dinoflagellates in the active condition, but only when killed by the iodine or bichloride methods. In red water plankton in which Amphidinium fusiforme is the dominant species, the Amphidinium cells tend to cling together in clumps, but no gelatinous envelopes can be demonstrated. In many of the clumps (although not in all), however, they may be seen to be clustered thickly about a cell of the Gymnodinium. This gelatinous envelope may well be a factor of importance in holding the organisms together, once they are massed by a favorable combination of light, water temperature, and tidal currents." Conjugation of G. breve was discussed by Wilson (USFWS, 1958). He said, "In the condition I have called conjugation I have never seen more than 2 organisms attached together. You may find them in various positions, but there is always a stalk-like process between two individuals." The size of G. breve is usually given as between 20 and 30μ. Wilson (USFWS, 1958) said, ". . . In certain cases in the field you will see a fairly large form which appears to have no chromatin material at all. . . ." CONTROL OF RED TIDE It is difficult to discuss control of red tide without first discussing the type and scope of the damage inflicted. This damage has three main aspects, 1) effect of red tide on the tourist business, 2) effect on the sport and commercial fisheries, and 3) effect on public health. Damage from Red-tide Outbreaks Since red-tide outbreaks usually start in the fall, just as the tourists are commencing to move south, an outbreak can cause very serious losses, especially at seaside communities in which the accommodation of tourists is often the chief, or sometimes the only, major business. Rotting fish on the beaches, and sometimes acrid aerosols containing toxin, will drive tourists away. From this standpoint alone, control is highly desirable. The effect on the fish populations has not been nearly as severe as the layman imagines when he hears of the death of millions of small fishes. The percentage kill is doubtless low. For instance, Lackey and Hynes (1955) stated, "... the last localized outbreaks of the 195354 Red Tide are only a few weeks past, yet sports fishing (grouper, speckled trout, mackerel, and redfish) has been generally good throughout the entire area. . . ." The kill of fishes by the 1946-47 red tide was estimated by Gunter, Williams, Davis, and Smith (1948) as 500 million fish. This figure may sound large, but actually it is not. If we realize that these fish will probably run no less than 10 to the pound, the total is only 50 million pounds. Every year about 1 billion pounds of menhaden are caught along a 300-mile stretch of the northern Gulf, but this enormous catch of a single species does not appear to be harming the supply. The effect of red tide on public health is rather debatable. For a short while during severe outbreaks there will be aerosols from breaking surf when the wind is blowing onshore. Long exposure close to, or on, the beach can be very irritating to the respiratory tract. A few people are so adversely affected that they must leave until the outbreak is over. More serious have been the questions regarding the safety of seafood products, shellfish in particular, during an outbreak; however, the Gulf Coast Shellfish Sanitation Research Center (1964) stated that, "... rigorous proof of the Red Tide organism as the cause of shellfish toxicity remains to be demonstrated." Since Gonyaulax and other dinoflagellates occur, often in fair abundance, in the red-tide area of the coast, it seems hardly fair even to attempt to indict G. breve without very definite proof. Oysters tend to occur, except when transplanted, in areas with salinities below those tolerated by G. breve (which is neritic), but well tolerated by several species of estuarine dinoflagellates. Methods of Control Methods of control of red tide depend largely on whether the objective is prevention, control, or mere 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 and remove, the dead fish washed or blown ashore. At best these are temporizing measures. As we have noted previously, fish-killing concentrations 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 impinge 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 maintaining 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 rejected (see Marvin 1958, 1959; Marvin, Lansford, and Wheeler, 1961). use 2. Keeping the nutrient level low by curbing of streams and bays for disposal of nutrient-rich sewage or other pollutants. Since G. breve can apparently thrive in nutrientpoor 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 streams, 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 convergences. 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 inhibitory organisms by special types of fertilization. This idea appears to be implicit 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 construction of underwater barriers, jetties, or similar structures at passes to restrict mixing of Gulf and 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 Committee at the 1958 symposium (USFWS, 1958). It certainly deserves full attention. Control of Outbreaks Only a few of either the preventive measures 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. Some of the untried suggestions undoubtedly have merit--it is a question of patient research, 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 B12 was suggested by Hutner and McLaughlin (1958), but dismissed with the comment that "truly enormous quantities of bacteria would be required. . . ." 2. Biological control through encouragement of predator organisms. The encouragement of predator organisms was mentioned by several authors. Galtsoff (1948) mentioned the ingestion of G. breve by a cladoceran, Evadne. Hutner and McLaughlin (1958) mentioned the ciliate protozoans and the luminous dinoflagellate, Noctiluca. Torrey (1902) mentioned the appearance of Noctiluca in great numbers toward the end of July and their devouring Gonyaulax "with avidity." There is no comment on how to encourage these predators, short of providing them a redtide bloom. 3. Physical control by high-frequency waves. Little attention has been paid to physical means of control. Lackey and Hynes (1955) stated, "... It has already been shown, however, 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 (1959) 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 Odum, Lackey, Hynes, and Marshall (1955) as a means 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 with practically 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 directly: 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 with copper sulfate to prevent the growth of bacteria after killing the dinoflagellates (Galtsoff, 1948). or 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 concentrated solution of 3,000 pounds of copper sulfate from the ballast tanks of the Alaska. In 1953 sacks of copper sulphate were towed from small boats off Anna Maria Key. Later a small area was dusted by plane. None of these experiments 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 discover 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 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. a on red SUGGESTIONS FOR FUTURE RESEARCH In summarizing research to date 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 solution 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 declined between outbreaks until, at times, the level has become too low to provide adequate 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 suggestions that were made. Perhaps some reorientation 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 compounds to discover one or more specific for G. breve. This work has resulted in a report by Marvin and Proctor (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 is photoautotrophic, requiring both light and CO2 for growth and survival. 3. Would a copper ore dike maintain a high enough level of copper in the water to inhibit growth of G. breve? The answer is no (Marvin, Lansford, and Wheeler, 1961). The Advisory Committee urged the Bureau of Commercial Fisheries to attempt to publish both the data and the results of its redtide investigations. Since 1958 the Bureau has published all its raw field data and a number of reports on both field and laboratory projects. Laboratory Studies of the Organism Laboratory studies of both unialgal and bacteria-free cultures have yielded considerable information on the physiology of G. breve. More work is needed, however, especially on the role of other plankton organisms in promoting or inhibiting growth. This type of work may involve the use of radioisotopes to trace the flow of nutrients. There has been much discussion of the possible role of chelators in stream water or surface runoff in promoting growth. In both of the above cases it is possible that experiments have been hampered by the very high surface: volume ratio of the test tubes in which most experiments have been carried out. In 1958 several advisers suggested that cultures be grown in large tanks to answer better such questions as killing concentrations of G. breve and the effect of dead fish, either in perpetuating a bloom, or possibly in creating lethal concentrations of bacteria. a Some have advocated attempting to cause a bloom of red tide by such measures as dumping a barge of dead fish, dumping large amounts of pollutants from selected localities, or by fertilizing an area containing organisms with specific nutrients. Most agreed that to gain sufficient control over the experiments, the studies might better be performed in large tanks. Discovering how to create bloom is the opposite approach from observing blooms in the field and then trying to decide the cause. We believe the problem should be approached from both directions. In any such tank experiments, we believe that an attempt should be made to imitate natural conditions insofar as practicable. Thus, a very large tank might offer a fine opportunity to test the role of convergences in concentrating the organisms, and perhaps to solve their ability to grow in water of low nutrient content. The life forms of G. breve have been observed, but work is needed to determine the factors causing encystment, the conditions under which cysts can survive, the length of time they can survive, and the conditions favoring resumption of the normal form. The winter survival of G. breve in the deeper (and warmer) offshore waters (as deep as 123 feet) has been stressed (Dragovich, 1960b; Dragovich and May, 1961; Finucane, 1960), but overwinter survival of encysted forms in the shallower inshore waters is a distinct possibility that requires investigation. Should this inshore survival occur it might be remotely possible, following heavy redtide outbreaks in the fall, to modify the sudden recurrences in the spring (as happened in 1947, 1954, and 1960) by destruction of the cysts on the bottom. Binary fission was the only method of reproduction observed by Lackey and Hynes (1955). Conjugation was also observed by Wilson (USFWS, 1958). Because it is apparently not often observed, the discovery of what favors conjugation and its role in maintaining population abundance might be important. Although the red-tide organism normally measures about 20 to 35 μ, large forms, perhaps up to 80 μ, have been observed. Wilson (USFWS, 1958) mentioned that occasionally in the field one observes "... a fairly large form which appears to have no chromatin material at all. . . ." He did not observe these in the laboratory. It would be of interest--perhaps of some importance--to discover whether this large form is a special life form of G. breve or perhaps a distinct species. Opinions seem to differ as to whether G. breve can form chains. Wilson (USFWS, 1958) said that cysts form chains, and that when the culture is stirred these tend to remain together, but he had never seen a chain formation of normal free-swimming cells. Collier (USFWS, 1958), however, mentioned watching the organisms form long chains. His observation was apparently made while he was watching a very high natural concentration--probably much higher than any encountered in the laboratory. It is possible that dense concentrations may cause the organisms to act in a different manner. The possibility that a difference in life forms or manner of reproduction may be triggered by excessively high concentrations deserves investigation. There appears to be some question whether changes in color of red-tide water are caused by density of the organisms, by the angle of the light, or by the age of the population. Wilson (USFWS, 1958) said that each culture seems to have a tendency to accumulate oil droplets with age, which will give a different color comprehension. If either color or oil accumulation could be used as a gross measure of population age, it might be useful in determining whether a population is increasing or declining. |