10 15 



SECONDS 



2 



25 



Figure 1 8-3. Example of reaction of a single stage 1 1 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 Uttle 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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