Figure 18-7. Examples of computer tracked paths for stage II 
Balanus improvisus nauplii and assigned rate of change of 
direction values (degrees/sec.): A) 114, B) 53, C) 152, D) 373. 
NOTE: Paths A, B are typical of control conditions; path C occurs more fre¬ 
quently with copper present; path D was observed only above 50 ppb copper. 
DISCUSSION 
Initial results have demonstrated possible use of invertebrate larval 
swimming behavior as a sublethal response index. It has also been shown that 
for this index to be reliable, the effects of basic experimental variables such as 
temperature and light regime on the swimming response of test organisms 
should be understood. 
Although previous studies on cirriped and brachyuran larvae (2, 11, 25) 
indicate no phototactic response is evident above 650 nm, cirriped nauplii 
appeared to exhibit a weak response to the present substage light. Spectral 
sensitivity of the species tested appears to extend further into the red than 
previously reported. 
Balanus venustus and B. amphitrite nauplii exhibited two responses to 
sudden changes in light. The cessation of swimming by nauplii following a 
sudden light decrease is similar to the “sinking response” described for 
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