100 - 
Figure 11-3. Batch variability in N. obsoletus larval 
survival upon exposure to "1.0" ppm fuel oil (WAF). 
NOTE: Experiment "A" employed 15 larvae/vial and ran 4 days. Experiment 
"B" employed 20 larvae/vial and ran 8 days. The range of mortality observed 
in the 3 replicates run at each concentration is indicated. Oil concentrations 
are reported as Mean ppm ± s.d. (N measurements). 
Static exposures of larval C. fornicata ran only three days. No mortality was 
observed at any oil level tested. However, no larvae were observed swimming at 
“1.0” ppm by day two. Activity was normal at lower oil concentrations. 
Moreover, the guts of larvae at “1.0” ppm were empty of food by the second 
day, whereas veligers at lower oil concentrations continued to feed during the 
three-day experiment. In the flow-through exposure, veligers held at “1.0” 
ppm also stopped swimming by the second day of the experiment. These larvae 
were alive but emaciated by day four, and dead by day six. Crepidnla fornicata 
larva had good survival at lower oil levels, although growth rates were affected 
as discussed below. 
Gastropod Reproduction 
Adults of N. obsoletus collected in February, 1976, and October, 1976, 
deposited their first egg capsules in laboratory control containers on 4/30/76 
and 5/6/77, respectively, when the water temperature warmed to 
approximately 10°C. Sastry (27) also obtained egg capsules at 10°C from N. 
obsoletus collected in January at Beaufort, North Carolina. 
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