occurs only sporadically and reports are few. 

 The senior author found no reports, for in- 

 stance, from Alaska, although he knows from 

 personal experience that streaks of water as 

 red as tonnato soup sometimes occur in 

 southeastern Alaska in late summer. 



The best docunnented reports of red tides 

 and mass mortalities conne from a few locali- 

 ties: The Malabar Coast of India, the coast 

 of northern Chile and Peru, near Walvis Bay 

 in Southwest Africa, Japan, and southern 

 California. Additionally, in many localities in 

 which blooms of toxic dinoflagellates are not 

 sufficiently dense to cause mortalities, the 

 ingested organisnas can render shellfish toxic 

 to humans. 



The distribution of the naked dinoflagellate, 

 Gymnodinium breve , that causes the Florida 

 red tide is not well known. It occurs in 

 Trinidad (Lackey, 1956) and is the chief 

 suspect in frequent fish mortalities near the 

 mouth of the Orinoco River in the Gulf of 

 Paria. There is considerable evidence that 

 G. breve may be distributed throughout the 

 Gulf of Mexico. The organism has caused 

 extensive fish nnortalities along the southern 

 coast of Texas, extending far down the Mexican 

 coast (Wilson and Ray, 1956; Gunter, 1952; 

 Lund, 1935). Wilson isolated G. breve from 

 Galveston waters (Collier, 1958b). Fishermen 

 report "red water" on the Campeche Banks, 

 but the causative agent is still unknown 

 (Graham, 1954). Because G. breve was not 

 identified until 1948 and is so fragile as to 

 resist collection by conventional methods, it 

 may be far more widely distributed than avail- 

 able records indicate. Although other toxic 

 dinoflagellates, such as Gonyaulax , occur in 

 Florida, it is probably safe to assume that 

 the earlier red tides were also caused by 

 C_. breve . Hutton (1956) reported a bloom of 

 Ceratium furca with counts as high as 

 17,600,000 cells per liter, but this was in 

 Hillsborough Bay (a part of Tampa Bay) which 

 is not normally invaded by G. breve on account 

 of the low salinity (see Ingle and Sykes, 1964), 



GENERAL CONDITIONS DURING 

 RED-TIDE OUTBREAKS 



Conditions conducive to overblooming of 

 dinoflagellates are suggested by numerous 

 reports of red-tide outbreaks in many locali- 

 •ties. These are discussed below. 



Temperature 



Red tides as a whole are less frequent and 

 less intense in temperate regions than in the 

 lower latitudes, where the hot weather during 

 outbreaks is often mentioned. These observa- 

 tions concerning hot weather may be a reflec- 

 tion of other conditions, such as a lack of 

 strong wind. Certainly the sea temperatures 



remain fairly low in regions of extensive up- 

 welling, such as the California and southwest 

 African coasts, where red tides often occur. 



Barker (1935) found the optimal range for 14 

 species of marine dinoflagellates to lie between 

 18° and 35 C. For Gymnodinium breve Finu- 

 cane (1960) stated that the optimum is 26° to 

 28° C, but that dense populations were ob- 

 served at 15° to 18° C. Aldrich (1959) exposed 

 800 individual cultures to controlled tempera- 

 tures and found no survival at 7° C. or below, 

 or at 32° C. and above. Populations did not 

 grow above 30° C, and multiplication was 

 visibly slowed but not halted at 15° C. 



Isopleths of abundance of G. breve against 

 tennperature and salinity (averages from 

 samples of 20 or nnore) from 7 years of field 

 data analyzed on the computer show that the 

 organisms appear to thrive from 16 to 27 C. 

 (fig. 2). Beyond this range organisms occurred 

 only in low abundance. These observations 

 agree rennarkably well with the laboratory 

 results of Aldrich (1959). 



The effect of cold waves in ending a bloom 

 has often been mentioned. After the heavy out- 

 break in the fall of 1957, Finucane (USFWS, 

 1958) said, "...There were several cold waves 

 in December and water temperature was as 

 low as 9.9° Centigrade. Following the cold front 

 we couldn't find any bugs north of Pass-a- 

 grille. . . ."Taylor ( 1917a, b) mentioned a severe 

 freeze in February 1917, following the heavy 

 fall outbreak of 1916, which did not recur in 

 1917. Gunter (USFWS, 1958) mentioned a 

 cold spell that brought freezing temperatures 

 to Miami and ended (temporarily at least) 

 the 1946 red tide outbreak. 



Salinity 



Dinoflagellates in general have a wide salin- 

 ity tolerance. The armored species are usually 



Figure 2. — Isopleth (0.01) of geometric mean of Gymno- 

 dinium breve per ml. showing relation of G. breve to 

 temperature and salinity. 



