brachyuran larvae (10). The increase in swimming velocity of larvae following 
light increase cannot be fully described without consideration of possible 
directional response. Of practical relevance to our video taping and analysis 
procedures is that both responses are of brief duration, limited to the first 
three to five seconds of an acute illumination change, and can be detected from 
calculations of the MLV. The significance of these responses are not yet 
understood. Similar behavioral characteristics were not observed in stage II 
nauplii of Chthamalus and are also reported lacking in Balanus balanoides (6). 
Temperature is known to directly affect swimming rate of invertebrate 
larvae (15, 23). All temperatures tested here on second stage nauplii were 
within ranges allowing complete development of the barnacles (14). It is clear 
for all species tested that small temperature shifts can alter swimming speeds. 
The basic influence of temperature observed on larval swimming rates is 
probably primarily a function of species and thermal history, yet initial results 
with these barnacle nauplii suggest other factors may prove significant. For 
example, Balanus improvisus collected from Rhode Island and South Carolina 
and maintained at identical laboratory conditions for over one month, released 
larvae having apparently different swimming rates relative to temperature. 
Maximum MLV occurred at 25°C for South Carolina larvae and at 22°C for 
Rhode Island larvae. Similar differences in response were observed in B. 
amphitrite from South Carolina and C. fragilis from Rhode Island. Replicate 
tests with different hatches are needed to confirm whether geographical 
variations persist. 
To determine whether swimming patterns of barnacle nauplii are altered by 
toxic substances, stage II nauplii were exposed to different copper 
concentrations. Our exposure time to copper was limited to 24 hours. No algae 
food was added during this period to preclude complexing of the metal by the 
algae. Deprivation of food for 24 hours is not deleterious to the larvae. A 24 
hour LC50 of between 200-350 ppb Cu for B. amphitrite nauplii at 20°C and 
between 150-200 ppb Cu for B. improvisus nauplii at 26°C was observed. 
Similar toxic concentrations have been reported for Balanus crenatus nauplii 
(19) and Balanus eburneus nauplii (5). Cyprid larvae or adults were more 
resistant to copper in both these studies. 
Differences in LC50’s observed for B. amphitrite and B. improvisus nauplii 
may be related to temperature. Higher temperatures can increase copper 
toxicity (3) or at least give this appearance in short-term experiments (21). 
Weiss (26), however, found B. amphitrite to be more tolerant of Cu than B. 
improvisus at settlement. In either case, toxic etlects of Cu are often 
cumulative (3); both LC50 levels and sublethal effects probably occur at lower 
concentrations with increased exposure times. 
285 
