NOTES 



TWO BLOOMS OF GYMNODINIUM SPLENDENS, 

 AN UNARMORED DINOFLAGELLATE 



Little is known about the ecology and physiology 

 of an unarmored dinoflagellate (30 to 50 /im), Gym- 

 nodinium splendens Lebour, although feeding 

 experiments have shown it to be an important 

 food source for certain marine herbivores. Lasker 

 et al. (1970) found that anchovy larvae may be 

 reared the first week upon unialgal suspensions of 

 G. splendens while Paffenhofer (1970, 1971) and 

 Barnett (1974) showed it to be a preferred food for 

 Calanus finmarchicus and larval stages of 

 Labidocera trispinosa. Pokorny and Gold (1973) 

 reported on cell ultrastructure of G. splendens, 

 Sweeney (1954) observed vitamin B12 

 requirements, and Thomas et al. (1973) described 

 optimal light and temperature requirements. In 

 addition to these laboratory studies, Loftus et al. 

 (1972) have noted G. splendens in a bloom of 

 diverse dinoflagellate species in Chesapeake Bay. 

 This note reports upon two field studies of 

 blooms of G. splendens. The first observation was 

 made in Coyote Bay of Bahia Concepcion, Gulf of 

 California, where G. splendens was the dominant 

 phytoplankter in March 1971. The second observa- 

 tion was made in March 1974, when large concen- 

 trations were observed in coastal waters of the 

 Southern California Bight. In both occurrences G. 

 splendens dominated the phytoplankton crop so 

 that measurements of primary production and the 

 chemical composition of suspended particles 

 allowed a reasonable description of this species. 



Gymnodinium splendens in Coyote Bay 



Coyote Bay Oat. 26°43.0'N, long. 111°53.0'W) of 

 Bahia Concepcion is well protected and shallow. 

 Chemical and physical observations were made 

 while the ship (RV E. B. Scripps) was at anchor in 

 20 m of water and included measurements of par- 

 ticulate adenosine triphosphate (Holm-Hansen 

 and Booth 1966) and chlorophyll (Yentsch and 

 Menzel 1963; Holm-Hansen et al. 1965), micro- 

 scopic examination of water samples preserved in 

 5% (V/V) buffered Formalin' (Utermohl 1958), 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



and determinations of primary production based 

 upon rates of incorporation of radioactive carbon 

 (Steemann Nielsen 1952). The depth distribution 

 of phytoplankton was recorded at regular inter- 

 vals by continuous vertical profiles to the bottom 

 with both a submersible transmissometer (Petzold 

 and Austin 1968) and a fluorometer attached to a 

 hose and submersible pump (Lorenzen 1966; 

 Kiefer and Austin 1974). The continuous profiles of 

 in situ fluorescence were translated into 

 chlorophyll a concentrations by frequent calibra- 

 tion with discrete samples which were analyzed 

 fluorometrically for chlorophyll and phaeophytin 

 concentration (Kiefer 1973). 



The five phytoplankters which occurred 

 together and were numerically most abundant in 

 Coyote Bay were: G. splendens (l.OxlOVliter), 

 Leptocylindrus danicus (3.4x lOVliter), Skele- 

 tonema costatum (1.4 X lOVliter), Cerataulina 

 bergonii (1.4x lO^/liter), and Thalassiothrix 

 frauenfeldii (4.0 x lOVliter). Chlorophyll concen- 

 tration varied with depth and ranged from 4.4 

 )Ltg/liter to 13 /tg/liter for numerous samplings of 

 the 20-m water column. Figure 1 shows a time 

 sequence of profiles of in situ fluorescence of 

 chlorophyll. Profiles of light transmission 

 displayed a similar stratified structure. The 

 increase in depth of the upper chlorophyll 

 maximum between 1845 and 2300 and the decrease 

 in depth between 2300 and 0720 the following day 

 indicated a diel migration of G. splendens. This 

 suggestion was supported by the predominance of 

 G. splendens in the maxima and by the 

 improbability of physical factors such as advection 

 or internal waves affecting such variations. Con- 

 ditions were calm at the sea surface and the water 

 column was isothermal with depth. 



The upper chlorophyll maximum (Figure 1) 

 moved downward at sunset with a velocity of 

 approximately 1.7 m/h. Such velocities are similar 

 to those of other dinoflagellates. For example, a 

 natural bloom of Ceratiumfurca occurring off the 

 southern California coast was observed to migrate 

 downward at 2 m/h and mass cultures of 

 Cachonina niei and Gonyaulax polyedra displayed 

 migratory rates of 1 to 2 m/h (Eppley et al. 1968). 

 Our observations suggested that a portion of the 

 G. splendens population moved upward between 

 2300 and 0400 the following day. Since sunrise was 



675 



