FISHERY BULLETIN: VOL. 75. NO. 3 



was heavily preyed upon by anchovy larvae even 

 though P. trochoideum are as small as the small- 

 est particles detected by Arthur ( 1976) in the guts 

 of larval anchovies. 



It appears that prey differ in their nutritional 

 value to anchovy larvae. Gymnodinium splendens 

 and Gonyaulax polyedra are readily eaten by an- 

 chovy larvae, but G. polyedra was an inadequate 

 food. Only 1 larva of the 74 that were reared on 

 an exclusive diet of G. polyedra survived for 

 10 days. Larvae reared on a diet of G. polyedra 

 supplemented with microzooplankton had sur- 

 vival rates that increased relative to the degree 

 of supplementation. Although certain species of 

 Gonyaulax are known to be toxic, it seems un- 

 likely that this was a cause of mortality in our 

 experiments because survival was good when lar- 

 vae were fed G. polyedra supplemented with 5 

 microzooplankters/ml. 



We offer two possible explanations for the dif- 

 ference in the nutritional value of the two dino- 

 flagellates: 1) G. polyedra is about 10 /xm smaller 

 in diameter than G. splendens. Therefore, on the 

 basis of volume alone, G. splendens could have 

 twice as many calories as Gonyaulax polyedra, 

 because the volume increases as the cube of the 

 radius in a sphere. 2) G. polyedra is armored while 

 Gymnodinium splendens is not, and, therefore, 

 G. splendens is presumably more, digestible by 

 anchovy larvae which have an undifferentiated 

 gut during the early stages of their development. 

 Lasker et al. ( 1970) found that the armored dino- 

 flagellate, Prorocentrum micans (27 x 38 /xm), 

 did not sustain life in first feeding anchovy larvae 

 but again, this organism is smaller than G. 

 splendens. 



Lasker (1975) concluded that the nearshore 

 area of the Southern California Bight was a good 

 feeding ground for first feeding anchovy larvae 

 during the spring of 1974 because of the high 

 concentrations of G. splendens found in the chloro- 

 phyll maximum layer. In this study, the survival 

 of anchovy larvae fed 100 G. splendens/m\ was 

 acceptable, and it did not differ from that of larvae 

 fed a G. splendens diet supplemented with micro- 

 zooplankton at concentrations up to 5 organisms/ 

 ml. Although larvae grew slightly faster when 

 given the microzooplankton, these results still 

 indicate that a larva could survive until an age 

 of 10 days without the high concentrations of 

 micronauplii that O'Connell and Raymond ( 1970) 

 found to be necessary. If anchovy larvae survive 

 to a size of 5 to 6 mm on G. splendens, their feeding 



582 



efficiency would be higher than smaller larvae 

 (Hunter 1972), and because of their larger size, 

 the volume of water that larvae could search for 

 food would also be increased. These factors would 

 reduce the concentration of microzooplankton 

 necessary for survival (Vlymen in press). 



During several sampling periods in 1975, 

 Lasker (in press) found that the chlorophyll maxi- 

 mum layer in the nearshore region of the South- 

 ern California Bight was dominated by Gonyaulax 

 polyedra or a variety of small diatoms. Our work 

 indicates that during the time periods when 

 these phytoplankters predominated, feeding con- 

 ditions for post yolk-sac anchovy larvae would 

 be less suitable than when G. splendens was 

 abundant. 



ACKNOWLEDGMENTS 



We thank James Alexander and Geoffrey Lewis 

 for their technical assistance and Charles Bary 

 for culturing the phytoplankton. Thanks also go 

 to Reuben Lasker and John Hunter for reviewing 

 the manuscript. This research was supported by 

 a grant to Reuben Lasker from the Brookhaven 

 National Laboratory. 



LITERATURE CITED 



ARTHUR, D. K. 



1976. Food and feeding of larvae of three fishes occurring 

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 74:517-530. 



Bainbridge, v., and D. C. T. Forsyth. 



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Beers, J. R., and G. L. Stewart. 



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