Figure 18-3. Example of reaction of a single stage 11 Balanus 
venustus nauplius to sudden light decrease. 
NOTE: Dashed line indicates time at which overhead white light was extin¬ 
guished. Filtered (830 nm peak transmission) substage light was present 
throughout experiment for recording purposes. 
Chthamalus fragilis exposed to similar light changes exhibited little response 
in terms of MLV. The distinctive response seen with Balanus nauplii was clearly 
absent. 
Response to Temperature 
Newly hatched nauplii from the same brood (incubated at 20°C) were 
subdivided and placed into various temperature boxes for 24 hours to test the 
effects of temperature on swimming velocity (Table 18-1). The metal 
lightshield, glass filters, and beaker with larvae were equilibrated to the test 
temperature, then transferred immediately to the microscope stage for brief 
taping. Readings with a temperature probe indicated a maximum 2°C shift 
toward ambient occurred during taping. 
Even with the potential of a 2°C deviation in test temperatures, certain 
geographical distinctions are suggested between swimming velocity and 
temperature (Table 18-1). Data from Balanus amphitrite and B. improvisus 
nauplii from South Carolina adults suggest a direct relationship of increased 
swimming velocity with increased temperature. In contrast, B. improvisus 
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