with the aid of a Quebec colony counter. Plates with either more 

 than 300 or less than 30 colonies were not used in quantitative 

 estimates except in a very few instances. The exceptions were in 

 cases where either the most dilute plates contained more than 300 

 colonies or the undiluted plate contained less than 30 colonies. 



The bacterial counts most likely represent minimal concen- 

 trations because nutritional and environmental requirements of 

 an entire bacterial population cannot be satisfied with any 

 one medium or with a single set of incubation conditions. We made 

 no attempt to enumerate anaerobic bacteria. All colonies except 

 those with the typical appearance of molds were counted, therefore, 

 any microorganisms producing bacteria-like colonies were included 

 in the counts. 



Since we could not prepare pour-plates of all water samples 

 immediately after collecting them, another possible source of error 

 in the counts should be considered. Both quantitative and qualitative 

 changes in the bacterial population may have occurred before some 

 of the samples were plated, particularly those plated several hours 

 or even days after collection. Immediately after collection all 

 water samples were refrigerated (^ C=) until shortly before preparing 

 the plates. In most cases the storage period did not exceed 6 

 hours. However, this period varied considerably in some experiments, 

 especially those in which several samples were counted. Consequently, 

 we have recorded the extremes of the storage period for each 

 experiment. 



Procedure for Enumerating Dinoflagellates 



The concentration of G. brevis and other dinoflagellates was 

 determined in two steps: (1) a preliminary counting of 1.0 ml, 

 0.1 ml, and 0.01 ml aliquots from a sample mixed by gently swirling 

 the tube (vigorously shaking frequently causes many of the organisms 

 to cytolyse) to determine sample size best for counting, and (2) 

 counting 3 to 9 aliquots of the quantity selected in the first step. 

 The latter counts were averaged to obtain the G. brevis concentrations. 

 The counts probably represent minimal levels because the organism 

 tends to disintegrate when manipulated. Because of this tendency, 

 only one aliquot was withdrawn at a time and it was counted immediately, 

 A wide field stereoscopic microscope with a magnification of 54X was 

 used in making the counts. 



EXPERIMENTS WITH UNIALGAL CULTURES OF 

 GYMJODINIUM BREVIS AND OTHER DINOFLAGELLATES 



Seven experiments testing the toxicity to fish of unialgal cultures 

 of G, brevis and some other dinoflagellates were performed. All of 

 these studies, even those which are preliminary such as experiments 

 1 through 3 J are presented because the details and results vary 

 considerably in some cases. In some experiments only one test fish 



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