LILLELUND and LASKER: PREDATION BY MARINE COPEPODS 



proportion to the number of Artemia nauplii 

 present. The results of these experiments are 

 shown in Figure 12. There was a 50% decrease 

 in mortality of larvae with L. trispinosa females, 

 L. jollae males, and L. trispinosa males when 

 the nauplii concentration was approximately 220, 

 150, and 100 nauplii /liter, respectively. The de- 

 crease in larval mortality is accentuated if Ar- 

 temia nauplii are offered to Labidocera when 

 older larvae are present. Fewer Artemia nauplii 

 need to be present to depress the predation mor- 

 tality on older larvae (Figure 13). The ease 

 with which Labidocera can captui'e Artemia may 

 make it less likely that fish larvae will be at- 

 tacked. As the larvae age, this effect is com- 

 pounded since it has become even more difficult 

 to catch larvae and hence relatively less taxing 

 for the copepod to take Artemia nauplii. 



L. trispinosa $ 

 L. jollae ^ 

 L trispinosa a' 



d 50 100 150 200 250 



^ Artemia NAUPLII PER LITER (seawater) 



Figure 12. — Predation by Labidocera jollae males and 

 both sexes of L. trispinosa on anchovy larvae when 

 Artemia nauplii were also available to the copepods. 

 Fifty percent reduction in larval mortality occurred 

 when Artemia nauplii numbered 220/liter with L. tris- 

 pinosa females, approximately 150/liter with L. jollae 

 males and 100/liter with L. trispinosa males. 



CALORIC REQUIREMENT OF L. jollae 

 AND L. trispinosa 



We noted that the vigor of Labidocera indi- 

 viduals declined with time if they were not fed 

 or fed only Artemia nauplii. For example, after 

 1 week in the laboratory the activity of copepods 

 fed only Artemia was diminished so that a cope- 

 pod's ability to capture larvae was about one- 



50 100 150 200 250 300 



Artemia NAUPLII (1 day old) PER LITER 



Figure 13. — The effect of the age of the anchovy larva 

 and the addition of an extra prey (Artemia nauplii) on 

 larval mortality due to predation by Labidocera tris- 

 pinosa females. 



half that of a newly caught copepod. Labidocera 

 died after 2 or 3 days of starvation. This was 

 preceded by a decrease in swimming activity 

 which was reflected in a lower respiration rate 

 and dry weight of individuals. In Figure 14 we 

 give comparative respiration rates and dry 

 weights for L. jollae females (a) newly caught, 

 (b) larval-fish fed, and (c) starved for 2 days. 

 These results show an enhanced respiratory rate 

 for fed and presumably healthier animals and a 

 drastic decline due to short term starvation. 



STARVED FOR 2 DAYS 



FRESH ANIMALS 



FED ANCHOVY AND SARDINE LARVAE 2 DAYS 



00 02 0.4 0.6 08 10 1,2 



is\ Og/COPEPOD PER HOUR 



STARVED 2 DAYS 



FRESH ANIMALS 



FED ANCHOVY AND SARDINE LARVAE FOR 2 DAYS 



000 0.10 Oil 012 013 014 015 



DRY WEIGHT (mg) 



016 



Figure 14. — Comparative oxygen consumption and indi- 

 vidual dry weight measurements of Labidocera jollae 

 females under starved and well-fed conditions at 18° C. 



663 



