LILLELUND and LASKER: PREDATION BY MARINE COPEPODS 



h I6r 



■15.4 



-^" 



L trispinosa % 

 L. jollae di L trispinosa <? 



Figure 8. — Predation by individual Labidocera jollae and 

 L. trispinosa under comparable prey density. Experi- 

 ments were conducted in the dark for 24 hr in 3500 ml. 

 Each circle represents the results of one experiment. 

 The horizontal bar is the mean value for each series of 

 experiments. 



long when it hatches from the egg. Yolk-sac 

 anchovy larvae have unpigmented eyes, lack a 

 mouth and gills, and the yolk is invested with 

 lipid (Bolin, 1936) ; when newly hatched the an- 

 chovy larva is very slightly buoyant. The newly 

 hatched larva remains motionless most of the 

 time at this stage and swims only sporadically. 

 As it develops, swimming activity increases, oc- 

 curring about 5 9r of the time at hatching to 25'^r 

 on the second day and 50 '^r by the third (John 

 R. Hunter, personal communication). Figure 9 

 indicates a rapid decline in predation in the dai-k 

 by L. trispinosa and L. jollae females as the larva 

 grows older, presumably as a result of the latter's 

 increased swimming and sensory ability. Ef- 

 fective predation is restricted therefore to yolk- 

 sac larvae. 



14 



12 



10 



I- 



o 

 o 



Q. 

 liJ 

 Q. 

 O 

 O 



cr 



UJ 



UJ 8 



< 

 > 



q: 

 < 



_i 



> 



o 



X 



L. jollae 



L. trispinosa % 



(2) (2) 

 o 



"0 24 48 72 96 120 144 

 AGE OF ANCHOVY LARVAE (hr) 



168 



Figure 9. — The effect of the age of the anchovy larva 

 on predation by Labidocera jollae and L. trispinosa fe- 

 males. Each open circle is the mean of the number of 

 experiments shown in parentheses. The age of the larva 

 at the beginning of each experiment is given on the 

 abscissa. 



EFFECT OF LARVAL ANCHOVY DENSITY 

 ON L. jollae PREDATION 



Given 2 to 3 days, single L. jollae females can 

 kill by capture or biting all of 30 young anchovy 

 larvae in 3500 ml. This is shown in a mortality 

 curve (Figure 10) constructed from the results 

 of a series of experiments, each of which had a 

 number of newly hatched larvae (30 or less) 

 at the start confined with a single L. jollae fe- 

 male. The density of larvae per unit volume 

 (within the limits of these experiments) seemed 

 to have little or no effect on the kill rate until 

 there was only one larva remaining per 700 ml, 

 when the rate due to predation by the copepod 

 declined drastically. Our experience with pre- 

 dation experiments in 3500 ml volumes suggested 

 that anchovy larvae were randomly distributed 

 in this relatively small volume and that in the 

 dark, at least, each L. jollae female could almost 



661 



