In developing a model for a bloom of Gonyaulax , Prakash (1975) suggested that 

 the process involved two distinct parts: initiation and continuation. Bloom 

 initiation requires specific biological and chemical conditions that would 

 allow exponential growth of a population. An example is the disruption of 

 cyst beds caused by hydrographic disturbances. Continuation of the bloom 

 would then involve hydrographic and meteorological factors that could act as 

 mechanisms to concentrate the bloom. If cysts were carried to warmer surfaces 

 or coastal waters in spring or summer, excystment could occur and may account 

 for reappearance of Gonyaulax in spring each year (personal communication from 

 C. M. Yentsch, Bigelow Laboratory, West Boothbay Harbor, ME; November, 1977). 



Factors of Abundance 



The ecology of Gonyaulax excavata has attracted the attention of an increasing 

 number of scientists in recent years. One of the most puzzling aspects of red 

 tide is that the blooms are composed almost entirely of this single species. 

 Thus, conditions that favor a bloom of Gonyaulax must be highly selective. 



Prakash (1967) found that in culture conditions the optimal temperature and 

 salinity for G. excavata were 59 to 66°F (15 to 19°C) and 19 to 20 ppt. He 

 has suggested that in coastal and estuarine conditions salinity has a greater 

 effect on the abundance of this organism than does temperature, although the 

 effect of temperature may be expressed through cyst formation. The motile 

 form of the organism is not found in nature at temperatures less than 4l°F (5° 

 C; Yentsch et al. 1975). The low salinity in upper estuaries may slow 

 filtration rates of shellfish to such an extent that the organisms do not take 

 in toxins at a harmful level. 



Nutrient requirements of red tide organisms are not well defined. Several 

 studies (Prakash 1967, 1975; Yentsch et al. 1975) have suggested that humic 

 matter from land runoff may be important in controlling concentrations of 

 dissolved trace metals for growth of the organism. Other research has focused 

 on the role of iron, vitamins, and organic materials in Gonyaulax nutrition. 

 The nitrogen and phosphorus requirements of Gonyaulax seem to be much lower 

 than those of other phytoplankton species (Yentsch and Yentsch 1977). 



Benthic organisms may ingest the cyst form of the species, and accumulate the 

 toxin in the absence of a bloom. One dense bed of these cysts has been 

 located off the Maine coast near Monhegan Island (personal communication from 

 C. M. Yentsch, Bigelow Laboratory, West Boothbay Harbor, ME; November, 1977). 

 Prakash (1967) notes that sea scallops in the Bay of Fundy reach maximum 

 levels of toxicity in winter, when cysts may be most abundant. 



Other factors that may influence the species abundance include predation, 

 competition, and day length. 



Importance to Humanity 



The toxins Gonyaulax produces, which are harmful to other marine species, 

 evoke a reaction in humans known as paralytic shellfish poisoning (PSP) . The 

 poison is a group of endotoxins contained within the cell of the 

 dinof lagellate that is released when the cell is broken during digestion by 

 the consumer. The endotoxins block the transmission of nerve impulses along 

 nerve fibers. 



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10-80 



