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 ( A T = 10.1 ± 
0.6°C). After the 15 minute exposure period, larvae were siphoned into the 
predation tank using silicon 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). This 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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