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 

 v^thin 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 CaroUna and C. fragilis from Rhode Island. Replicate 

 tests v^th 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 concen- 

 trations. Our exposure time to copper was limited to 24 hours. No algal 

 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 LCSO'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 effects of Cu are often 

 cumulative (3); both LC50 levels and sublethal effects probably occur at lower 

 concentrations with increased exposure times. 



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