342 University of California Publications in Zoology [Vol.22 



DINOFLAGEL.L A TES 



Although some dinoflagellates are nearly always present in 

 plankton catches taken in the San Diego region, they are often very 

 few, and they are rarely so numerous as diatoms. This deficiency 

 in numbers is compensated to some extent by the fact that many 

 prominent dinoflagellates arc larger than any planktonic diatom cells 

 and also by the fact that living substance constitutes a larger part of 

 the cell body in dinoflagellates than it does in diatoms. But even 

 when we accept the statement made by Johnstone (1908, p. 192) that 

 one peridinian contains as much dry matter as twelve diatoms, it still 

 appears that dinoflagellate production over long periods of time is 

 distinctly less than diatom production, volumetrieally as well as 

 numerically. As to the four months now under discussion, however, 

 we may note that although dinoflagellates were found in distinctly 

 greater numbers than diatoms only in November, in October and 

 December their numbers were one-eighth and one-fourth as great, 

 respectively, as those of diatoms, which according to the ratio men- 

 tioned by Johnstone would indicate that they were volumetrieally 

 more important than diatoms in three months out of the four. 



At least a few dinoflagellates were present in every catch made at 

 this time. Their distribution was somewhat irregular though not so 

 markedly so as that of the diatoms. The extremes were not so great 

 and the representation was more constant in spite of the generally 

 smaller numbers. This, however, was offset to some extent by the 

 more frequent and sudden changes in numbers (fig. 2). In figure 2 

 the areas filled in solid black indicate the relative average numbers 

 found in each five day period (including ten catches), except in 

 October and December where the last period consists of six days with 

 twelve catches. 



The general features of distribution in the four months seem to be 

 essentially similar to those of distribution reported for other localities. 

 As in the case of the large diatom pulse in September, the largest 

 dinoflagellate pulse, which came in November, was preceded for a day 

 or two by strong currents of water from the north and was also 

 accompanied by moderate currents from that direction. While it is 

 not probable that these currents flowed continuously in the one 

 direction, it is probable that the main shift of the water mass was that 

 way. A successful recording apparatus for water currents was put 

 in operation at one time by our hydrographer, Dr. 0. F. McEwen, but 



