University of the West Indies 

 Cave Hill Campus, P.O. Box 6U 

 Barbados, West Indies 



Bellairs Research Institute 



ofMcGill University 

 St. James 

 Barbados, West Indies 



ascent in the early morning and maintenance of a 

 deeper distribution at night. This pattern was similar 

 to that observed by Kiefer and Lasker (1975) for this 

 Wayne Hunte species in the Gulf of California. Vertical chlorophyll 

 a profiles indicated the cells rose in the morning and 

 descended in the evening. The present study was 

 undertaken to measure swimming speeds of G. 

 splendens under different temperature conditions. 

 The observed speeds vary with temperature and are 

 similar to those calculated from field studies. 



EFFECTS OF TEMPERATURE ON 



SWIMMING SPEED OF THE DINOFLAGELLATE 



GYMNODINIUM SPLENDENS 



Dinoflagellate blooms or red tides frequently occur 

 in a stratified water column having low nutrients 

 near the surface (Huntsman et al. 1981). Under these 

 conditions dinoflagellates have a competitive advan- 

 tage over other phytoplankton due to their motility 

 and diel vertical migration pattern. In the absence 

 of turbulence, active swimming allows them to over- 

 come sinking and thereby, remain close to the sur- 

 face The normal diel vertical migration consists of 

 an ascent to some minimum depth during the day 

 and descent to a maximum depth at the night 

 (reviewed by Forward 1976). Through this pattern 

 they have access to nutrients over the area covered 

 by migration and they can migrate to the surface 

 during the day to obtain more light for photosyn- 

 thesis (Ryther 1955; Margalef 1978; Huntsman et 

 al. 1981). 



The success of dinoflagellates depends to a great 

 extent upon their swimming capability. There have 

 been few measurements of actual swimming speeds 

 of individual dinoflagellates (eg., Hand et al. 1965) 

 or estimates of speeds from population movements 

 during migration (Eppley et al. 1968; Kamykowski 

 and Zentara 1977). This is unfortunate because such 

 measurements are necessary to estimate the depth 

 of the water column available to dinoflagellates for 

 nutrients during migration. 



The most pronounced and widespread dinoflagel- 

 late blooms off the coast of Peru are caused by Gym- 

 nodinium splendens Lebour. Blooms occur most 

 frequently during the summer and are usually asso- 

 ciated with the phenomenon of El Nino (Rojas de 

 Mendiola 1979). At the beginning of the 1976 El 

 Nino, there was a major bloom of G. splendens. 

 Blasco's (1979) surface measurements during this 

 bloom indicated the dinoflagellate vertically 

 migrated with the suggested pattern involving an 



Materials and Methods 



The dinoflagellate Gymnodinium splendens 

 Lebour was cultured as described previously (For- 

 ward 1974) in a Sherer 1 environmental chamber 

 (Model CEL-44) on a 14:10 LD cycle at a salinity of 

 about 34 ppt. All experiments were performed in the 

 middle 4 h of the light phase with cultures having 

 densities of about 2,000 cells/mL. This cell density 

 was used because it was similar to that used in past 

 studies (Forward 1974, 1977) and thus past results 

 can be applied to the present study. Swimming speed 

 during phototaxis was only measured during a 

 specific time interval because there is a circadian 

 rhythm in phototaxis (Forward 1974). Gymnodinium 

 splendens shows about average levels of phototaxis 

 during the middle 4 h of the light phase It is not 

 known whether there is a similar rhythm in swim- 

 ming. 



Subcultures were exposed to two sets of temper- 

 ature conditions to test for the effects of 1) tem- 

 perature acclimation and 2) acute temperature 

 changes upon swimming speed. In the first tests cells 

 were acclimated to selected temperatures from 13° 

 to 25 °C for at least 5 d prior to swimming speed 

 measurements. These temperatures were used 

 because they encompass the range in which the cells 

 grow at reasonable rates (Thomas et al. 1973). For 

 the second tests, cultures were acclimated to 19°C 

 for at least 5 d. At the time of testing cultures were 

 exposed to an acute temperature change by placing 

 the flasks in a water bath set at selected tempera- 

 tures for 0.5 h, after which time swimming speed 

 was measured. Room lights were on during this 0.5-h 

 period. The temperature of the room in which swim- 

 ming was measured was regulated to approximate- 

 ly each test temperature Each test was performed 

 on four separate subscultures. 



To measure swimming speeds, a sample of cells 

 was removed from a subculture and placed in a clear 



1 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



460 



FISHERY BULLETIN: VOL. 84, NO. 2, 1986. 



