Oil exposure modified the normal pattern of egg capsule deposition by adult 
N. obsoletus (Figures 11-5 and 11-6). Control snails tended to climb up the 
sides of the containers and deposit egg capsules mostly on the underside of the 
lid (Table 11-4). In the intertidal zone where spawning occurs, this behavior 
would contribute to placement of egg capsules into high-humidity 
environments where exposure of developing embryos to desiccation stress 
would be minimized (23). In contrast,TV. obsoletus exposed to the “0.01” ppm 
and “0.1” ppm oil deposited capsules primarily on the container sides (Table 
11-4). This effect was consistently most pronounced in May and June, at the 
beginning of the reproductive season (Figures 11-5 and 11-6). After 15-20 
days, lid deposition began to increase for oil-exposed snails in both runs. 
However, lid deposition by control snails remained greater than that by 
LlI 
Q 
Figure 11-5. influence of No. 2 fuel oil on egg capsule 
deposition behavior of N. obsoletus, 1976. 
NOTE: Exposures were initiated 2/13/76. Each point represents data pooled 
from 2-4 replicate containers holding fifty snails each. The total number of 
capsules deposited were: 19,492 (control); 9,894 ("0.01" ppm); 11,287 ("0.1" 
ppm), indicates the transfer of two control containers to "0.01" ppm. Mean 
total petroleum hydrocarbon concentrations ± s.d. (N) at each nominal con¬ 
centration were "0.01" ppm: 0.020 ±0.008 (9); "0.1" ppm: 0.082 ±0 044 
(20). 
146 
