FISHERY BULLETIN: VOL. 69. NO. 3 



35 r 



24 48 



HOURS 



Figure 10.— Survival of 0- to 1-day-old anchovy larvae 

 in the presence of a single Labidocera jollae female. 

 The curve is a composite from a series of experiments 

 in 3500 ml starting at different larval densities per 

 copepod where the time was noted after the capture of 

 a number of larvae. The numbers in parentheses indi- 

 cate the number of experiments ending at each point. 



completely search half this volume in 24 hr, re- 

 sulting in continuing random contact with and 

 killing of most, although not all, of the suspended 

 larvae when two or more L. joUae females were 

 present. 



THE EFFECT OF AN ADDITIONAL PREY 

 ON LARVAL PREDATION BY Labidocera 



Recent experiments by Brooks (1970) with 

 Labidocera trispinosa showed that this copepod 

 selects Artemia salina nauplii over copepod nau- 

 plii from the plankton. She concluded that Ar- 

 temia nauplii are selectively grazed because they 

 are relatively less mobile, hence more easily 

 captured. 



We tested predation by L. trispinosa on Arte- 

 mia nauplii and found that grazing corresponded 

 roughly to the results we obtained when fish 

 larvae alone were killed, i.e., up to a certain 

 concentration all Artemia nauplii were killed 

 in the experimental container in the dark over 

 24 hr. Survivors were found only if the number 

 of nauplii exceeded 11-14 nauplii 'liter 'copepod. 

 As the density of nauplii was increased more 

 were killed. This result was the same whether 

 experiments were performed in 3500-ml beakers 

 or in 200-ml Petri dishes (Figure 11). 



When Artemia nauplii in various concentra- 

 tions and 30 anchovy larvae were offered to- 

 gether to five L. jollae males or five L. trispinosa 

 males or females, larval mortality decreased in 



100 



CM 



Q 

 O 

 0. 

 LlJ 

 Q. 

 O 

 <J 



cr 

 iij 



Q. 



20 40 60 80 100 



Artemia NAUPLII PER COPEPOD 



Figure 11. — Mortality of Artemia nauplii due to Labido- 

 cera trispiiiosa female predation at different densities 

 of nauplii per copepod. Closed circles indicate experi- 

 ments done in 200-ml Petri dishes. 



662 



