Response to Light 
Nauplii used in all experiments were light adapted as fluorescent bulbs in 
the temperature boxes were on continuously. When transferred to the darkfield 
stage, larvae tended to disperse to the beaker walls with ceiling lights on. With 
these lights extinguished, nauplii tended to swim away from the beaker walls. 
Direction of travel upon entering or leaving the camera field exhibited no 
particular orientation. Ongoing studies indicate dark adapted B. amphitrite 
nauplii will exhibit a weak photonegative response to substage light over a 
five-minute period (Forward & Lang, personal observation). 
Balanus spp. stage II nauplii exhibit similar response to sudden changes in 
light intensity. When overhead white room lights are turned on, Balanus nauplii 
will approximately double linear velocities, then within 4-6 seconds return to 
initial swimming speeds (Figure 18-2). Turning overhead lights off has 
essentially the opposite effect; nauplii will cease locomotion for about five 
seconds and then return to initial swimming speeds (Figure 18-3). 
Figure 18-2. Example of running average linear velocity 
(mm/sec) for sample of ten stage II Balanus venustus 
nauplii exposed to sudden light increase. 
NOTE: Dashed line indicates time at which overhead white light stimulus was 
applied. Filtered (820 nm peak transmission) substage light was present 
throughout experiment for recording purposes. 
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