during a cruise on RV David Starr Jordan. Sta- 

 tions in the sampling program extended along the 

 20-fathom contour from Malibu (lat. 34°00.8'N, 

 long. 118°40.6'W) south to San Onofre (lat. 

 32°56.0'N, long. 117°17.4'W). Intermediate sta- 

 tions included Manhattan Beach (lat. 33°52.5'N, 

 long. 118°27.0'W), Seal Beach (lat. 33°36.5'N, long. 

 119°04.3'W), and Dana Point (lat. 33°26.3'N, long. 

 117°42.8'W). A sixth station was on the 270- 

 fathom contour off Laguna Beach (lat. 33°30.8'N, 

 long. 117°50.3'W). 



Continuous vertical profiles of in situ chlorophyll 

 fluorescence were made to a depth of 35 m. Water 

 from the outflow of the fluorometer was collected 

 at the surface and within the fluorescence 

 maximum. Three analyses were made on sub- 

 samples of water from the two depths. First, the 

 size distribution of suspended particles was im- 

 mediately determined with an electronic particle 

 counter (model Ta Coulter Counter). We ac- 

 cumulated counts in the upper nine channels which 

 gave us a frequency distribution for particles with 

 equivalent diameters ranging from 20 to 128 /^m. 

 Second, subsamples were preserved in 5% For- 

 malin for species determination. Third, the 

 chlorophyll a concentration in each subsample was 

 determined fluorometrically for acetone extracts 

 of filtered particles. 



Vertical profiles made at various times of the 

 day and night at each of the six stations on the 

 20-fathom contour were characterized by a 

 unimodal distribution of chlorophyll. The 

 chlorophyll maximum varied little in depth from 

 15 to 20 m within a moderately developed ther- 

 mocline, and was most often less than 4 m thick. At 

 these stations, G. splendens contributed most of 

 the phytoplankton crop within the maxima. 

 However, in surface waters it contributed a much 

 smaller fraction of the crop. The highest concen- 

 tration (Figure 2) of G. splendens was within the 

 well-defined maximum at Seal Beach where its 

 concentration reached 4x10^ cells/liter 

 (chlorophyll a = 42.0/xg/liter). The lowest concen- 

 tration within a maximum was at Manhattan 

 Beach, 1.2x10'' cells/liter (chlorophyll a = 1.3 

 /Ag/liter. 



The predominance of G. splendens in the 

 chlorophyll maximum was also evident from the 

 particle size distributions obtained with the elec- 

 tronic particle counter. Within the maximum, 

 particles with equivalent diameters between 36 

 and 57 fxm far outnumbered smaller- and larger- 

 sized particles. In surface waters the smaller-sized 



CHLOROPHYLL a ( ^g/L ) 



I? 24 36 48 



T T" 1 1 1 1 1 



SEAL BEACH STATION 



3/21/74 



0845 



I 

 I- 



CL 



CHLOROPHYLL a ( ^g / L ) 

 0.5 1.0 1.5 2.0 2.5 



20 



30 



1 r 



MALIBU STATION 



3/20/74 



0935 



Figure 2.-Profiles of the concentration of chlorophyll a based 

 upon fluorescence profiles at two stations along the 20-fathom 

 contour of the Southern California Bight. The subsurface 

 maxima are predominantly composed of Gymnodinium 

 splendens. 



particles outnumbered particles of the size of G. 

 splendens. The other phytoplankton in surface 

 waters included Ceratium furca and C. kofoidii, 

 Dinophysis acuminata, and a species of 

 Gyrodinium. Very few diatoms were present. 



It appeared that the bloom of G. splendens dis- 

 sipated seaward since the subsurface chlorophyll 

 maximum was poorly developed at the Laguna 

 Beach station which was on the 270-fathom con- 

 tour. Here the concentration of chlorophyll in the 

 maximum was only 0.76)u,g/liter, while the concen- 

 tration at the surface was 0.63 /ig/liter. In addi- 

 tion, both the particle size distribution and 

 microscopic counts indicated a more diverse as- 

 semblage of dinoflagellate species at this station, 

 with the unarmored dinoflagellate Cochlodinium 

 catenatum being most abundant. 



Thus, the bloom of G. splendens appeared to be 

 limited to nearshore waters, in a band extending 

 as far as 100 km along the coast. This subsurface 

 bloom was presumed to be a large food source for 

 planktonic herbivores, but more field sampling is 

 necessary to determine whether the bloom is a 

 seasonal occurrence. In another paper, Lasker 

 (1975) describes the feeding responses of anchovy 

 larvae to these natural concentrations of 

 G. splendens. 



Acknowledgments 



This work was supported, in part, by the Na- 

 tional Science Foundation (GA-36511). We thank 

 Eileen Setzler, Anne Dodson, and Freda Reid for 



677 



