cuvette The cells were viewed by the closed circuit 

 video system described by Forward (1974). During 

 random swimming the cells can move in any direc- 

 tion and are not necessarily moving in the plane of 

 view of the video camera. Thus measurements of 

 swimming speeds during random swimming tend to 

 underestimate true speed. To prevent this problem, 

 cells were stimulated horizontally with light and 

 speed measured during oriented swimming toward 

 the light (positive phototaxis). Room lights were off 

 during light stimulation. 



The light stimulus was a tungsten light source 

 filtered with a 4-96 Corning filter. The spectral com- 

 position of the light was similar to the spectral sen- 

 sitivity of phototaxis of G. splendens (Forward 1974). 

 A constant light intensity of 4.79 x 10 2 Wm~ 2 , as 

 measured with an EG and G radiometer (Model 550) 

 and calculated at 465 nm, was used for all tests 

 because maximum positive phototaxis occurs in this 

 intensity range, and it was necessary to measure 

 swimming speed during phototaxis. Swimming was 

 recorded on video tape and speed analyzed using 

 previous techniques (Forward 1974). 



Results 



Swimming speed varied greatly with temperature 

 (Fig. 1) as mean speeds approximately double upon 

 acclimation to temperatures between 13° and 25 °C 

 (0.56 h _1 to 1.16 mh _1 ). The dinoflagellate seems 



capable of limited temperature acclimation. If the 

 cells were acclimated to 19°C and suddenly exposed 

 to other temperatures, there was always a signifi- 

 cant difference (Student's t test; P < 0.001) between 

 these mean speeds and those upon acclimation. At 

 a lower temperature of 13 °C the acclimation speed 

 was higher; while at temperatures above 19 °C, the 

 acclimation speeds were lower. This trend is expected 

 with acclimation. 



The effects of temperature can be further assessed 

 by calculating the temperature coefficients upon ac- 

 climation and exposure to acute temperature 

 changes (Table 1). The Q 10 values for acute changes 

 are always higher than those upon acclimation, which 

 is expected if swimming rates are adjusted through 

 acclimation. When acclimated to temperatures be- 

 tween 13° and 19°C, the cells showed total compen- 

 sation (Q 10 = 0.98). In contrast, they were less able 

 to adjust their rates upon acclimation to higher tem- 

 peratures between 19° and 25°C (Q 10 = 3.42). Par- 

 tial acclimation occurred over this temperature 



Table 1.— Temperature coefficient values for the 

 dinoflagellate Gymnodinium splendens upon tem- 

 perature acclimation and exposure to acute 

 changes in temperature. 



Temperature 

 range 



Acute 

 Q10 



Acclimation 



Q10 



13°-19°C 

 19°-25°C 



1.47 

 4.68 



0.98 

 3.42 



13 15 17 19 21 23 25 



Temperature (°C) 



Figure 1.— Swimming speeds of the dinoflagellate Gymnodinium 

 splendens upon acclimation to various temperatures (solid line). The 

 effect of acute temperature change was measured by acclimating the 

 animals to 19°C and measuring speeds upon exposure to other 

 temperatures (dashed line). The number beside the points are the sam- 

 ple sizes and the vertical bars are standard errors. 



461 



