SECT. 2] ORGANIC REGULATION OF PHYTOPLANKTON FERTILITY 189 



are due to red-pigmented dinoflagellates, other discolorations (brown, yellow, 

 green or cloudy) are also responsible for producing mass mortality ; conversely 

 some red blooms like the ones of Trichodesmium erythreum (a red-pigmented 

 blue-green alga) in the Red Sea, Indian Ocean and the Sea of California are 

 generally harmless. The poisonous blooms, though not annual, recur in certain 

 coastal regions : in general, where fertilization occurs (upwelling, pollution, 

 heavy soil runoffs). Maps of bloom localities are given by Hayes and Austin 

 (1951) and Ballantine and Abbott (1957); Brongersma-Sanders (1957) gives 

 a detailed review of the outbreaks, the causative agents, and an impressive 

 bibliography. 



Most of the mortalities are due to dinoflagellates, specifically to Gonyaulax 

 2)olyedra, G. monilata, Gymnodinium splendens, G. breve, G. mikimotoi, G. 

 galatheanwm, Cochlodinium catenatum, Exuviaella baltica and Pyrodinium 

 phoneus. Two other dinoflagellates, Gonyaulax catenella and G. tamarensis, do 

 not cause mortality of marine organisms, including shellfish, but are ingested 

 by shellfish, which concentrate the poison in the siphon or digestive glands and 

 so become poisonous to man. Two other algae, the chloromonadine Horniella 

 marina (Subrahmanyan, 1954) and the diatom Thalassiosira decipiens (Takano, 

 1956), caused, respectively, extensive mortalities off the Malabar Coast and in 

 Tokyo Bay. Mortalities of fishes in brackish waters in Denmark (Otterstrom 

 and Nielsen, 1939) and in fish ponds in Israel (Shilo and Aschner, 1953) are 

 caused by the chrysomonad Prymnesium parvum. 



Mass mortalities occur at the peak of the bloom. In bacteria-free cultures of 

 Gonyaulax catenella, the toxin is localized in the cells during the logarithmic 

 phase of growth and accumulates in the medium, when death and disintegration 

 affect the population (Provasoli and McLaughlin, unpublished). This does not 

 exclude some toxin excretion by actively dividing cells, i.e. concentrations 

 below the sensitivity limit of the mouse bioassay. The ecological situation may 

 be similar ; toxic levels may be reached only when large numbers of dino- 

 flagellates are senescent or dying. 



A wealth of information on the poison of Gonyaulax catenella and Pry- 

 mnesium parvum (Schantz, 1960; Burke et al., 1960; Shilo and Rosenberger, 

 1960) and other products of marine organisms appeared in vol. 90, pp. 615-950, 

 of the Ann. N.Y. Acad. Sci. devoted to "The biochemistry and pharmacology 

 of compounds derived from marine organisms". 



If the poisons of other dinoflagellates are as potent as the one of Gonyaulax 

 catenella, we have another example of extremely active biological substances 

 released in sea-water. The poison of Gonyaulax catenella is one of the most 

 potent known, i.e. 1 mouse unit = 0.18 [i.g (1 unit is the dose killing all 20-g 

 mice in 7-15 min) ; the lethal dose for man = 3-4 mg. This neurotoxin, unlike 

 botulinum toxin, is a strongly basic nitrogeneous compound of low molecular 

 weight (372), yielding under various oxidations and hydrolytic procedures 

 guanidopropionic acid, guanidine, urea, ammonia and carbon dioxide (Schantz, 

 1960). A survey on the production of poisons by many dinoflagellates reared in 

 bacteria- free culture is under way at the Haskins Laboratories. 



