to 30.0 ± 0.6^C (A T = 9.7 ± 0.7°C) and beakers were placed into the heated 

 water at six minute intervals. Containers were aerated throughout the shock 

 procedure. As a 15 minute exposure period was completed, a beaker was 

 immersed in seawater 1°C above ambient for a five minute cooling period. The 

 larvae were introduced into predation tanks via a funnel filled with incoming 

 seawater (Figure 19-1). Larvae were added at six minute intervals, and most 

 larvae were eaten by the predator within the first three minutes following 

 introduction. All control larvae were treated in the same manner as shocked 

 larvae, but with transfer containers held at ambient water temperature rather 

 than a higher temperature. 



Larvae of Paralichthys dentatus are prone to damage in screened beakers 

 because of weak swimming ability and great sensitivity to handling (Grace 

 MacPhee, personal communication). Therefore, intact 100 ml polypropylene 

 beakers were used as transfer vessels. Ambient bay water temperature during 

 these tests was 15.1 ± 0.8°C. Groups of 10 larvae were shocked by gently 

 pouring the contents of each 100 ml beaker into a glass culture bowl (12.5 cm 

 dia.) containing 100 ml of seawater preheated to 25.2 ± 0.8°C (^T = 10.1 ± 

 0.6 C). After the 15 minute exposure period, larvae were siphoned into the 

 predation tank using siHcon tubing (9.5 mm dia.). Introductions of larvae to 

 the thermal treatment were again staggered at six minute intervals, as with M. 

 menidia. Control larvae were treated in the same manner as shocked larvae, but 

 with transfer to 100 ml of seawater at ambient water temperature. 



Quantifying Predator-Prey Interactions 



During the predation tests, all attacks, captures, and escapes were observed 

 from below and recorded using an Esterline-Angus event recorder. The best 

 visual field for recording observations was achieved by placing two opposing 

 light sources (two fluorescent bulbs) above, yet just outside of the visual range 

 of an observer directly below the tanks, and placing a flat black background 

 over the tanks (Figure 19-1). Tliis system permitted accurate recording of 

 predator-prey interactions involving organisms as small as four mm. 

 Significance of changes in escape probabilities, expressed as no. escapes/attack, 

 were tested using the Wilcoxon distribution-free rank sum test (13). 



RESULTS 



Results of predation tests for Menidia menidia are grouped by prey age 

 categories (Table 19-1). The two oldest larval groups of M. menidia (four week 

 and six week old) experienced a significant decrease (P < .01) in the number of 

 attacks, escapes and escapes/attack for shock tests relative to control groups. 

 The two youngest age groups of this species (newly hatched and two week old) 

 did not show significant treatment differences in any of the parameters 

 measured. 



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