For 24 hour exposures, concentrations of Cu below 100 ppb were clearly 
sublethal to the nauplii tested. Delay in development of B. improvisus nauplii 
occurred at 50 ppb Cu and changes in swimming behavior were evident at 
15-25 ppb Cu. At the lowest Cu test levels, responses were restricted to 
increased MLV, but at higher sublethal concentrations MLV was depressed and 
swimming patterns became atypical. A stimulatory effect of very low levels of 
copper on swimming activity has also been reported for brook trout (9.5 ppb 
Cu) (9) and with sea urchin sperm (<20 ppb Cu) (28). 
Forward and Costlow (12) also observed increased swimming activity of 
crab larvae exposed to 0.1 ppm of an insect juvenile hormone mimic, although 
larval development was not perceptively affected until 1.0 ppm was reached. 
On the other hand, sublethal concentrations of mercury and oil are reported to 
depress activity of marine crustaceans at nearly all levels tested (8, 18). 
Stebbing (23) suggests that apparent stimulatory effects of heavy metal ions on 
growth in marine hydriods and other groups are often only temporary and may 
represent a normal response to stressors. 
Observations on swimming of B. improvisus nauplii indicate that not only 
the linear velocity, but also the pattern is altered by Cu. Nauplii swimming in 
convoluted paths (Figure 18-7) tends to increase in number in the presence of 
copper above control levels. As copper concentrations exceed 50 ppb, paths 
with a distinct “wobble” became evident (Figure 18-7). This latter pattern is 
possibly a consequence of impaired or abnormal beating of appendages. This 
would lead to reduced feeding abilities, as feeding in cirriped larvae is a direct 
function of appendage movement. The increased development time to cyprid 
observed at higher sublethal copper concentrations may be the result of 
difficulties in feeding. 
The present study has consistently observed altered swimming behavior of 
cirriped larvae at Cu concentrations far below 24 hour toxic levels. Basic 
changes in swimming speed per se may prove useful indicators of pollution 
stress, but also of great interest are additional effects on larval motile responses 
to environmental stimuli or cues (light, chemical, gravity, etc.). The latter may 
prove more meaningful in predicting safe levels of pollutants. If short-term 
behavioral reaction can be satisfactorly correlated with long-term detrimental 
effects, the potential exists for rapid screening of toxic levels using this motile 
behavioral qualification technique. Further studies relating observed behavioral 
responses to other physiological parameters, and ultimately larval success, are 
planned. 
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