100 
Figure 11-4. Survival of C. irroratus during development 
at different oil concentrations. 
NOTE: Mean oil concentrations ± s.d. (N) were "0.01" ppm: 0.011 ppm 
±0.009 (14); "0.1" ppm: 0.094 ppm ±0.027 (14); "1.0" ppm: 0.913 ppm ± 
0.210 (14). 
Onset of egg capsule deposition by snails exposed to “0.01” ppm and “0.1” 
ppm was delayed by about two weeks relative to controls in 1976, and delayed 
up to one week in 1977. Encapsulated embryos produced by these oil-exposed 
snails, and transferred to control conditions, developed to hatching without 
noticeable abnormality. In a mid-summer experiment, control individuals 
produced many capsules within three days of collection from the field, but 
those held at “1.0” ppm never deposited any capsules. 
Egg capsule production is used here as an index of fecundity for both N. 
obsoletus and U. cinerea , since exposure to oil did not alter the average number 
of eggs per capsule (Table 11-2). 
Egg capsule production by N. obsoletus held at “0.1” ppm may be reduced 
relative to control, and “0.01” ppm snails (Table 11-3, line “e”), although 
these data are insufficient for statistical analysis. Results are inconclusive due 
to the death of an unknown number of females during the test breeding period, 
precluding accurate calculation of individual fecundity. 
143 
