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 higli-humidity 

 environments where exposure of developing embryos to desiccation stress 

 would be minimized (23). In contrast, M 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 

 begirming 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 



iij 

 o 



CO 



_l 

 Q. 



< 

 o 



CO 

 UJ 



_i 

 m 

 < 



12 - 



6 8- 



Q - 



CONTROL, 



O 4 - 



d 5/5 5/12 



5/25 



6/3 6/10 

 DATE 



7/8 7/15 



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). Arrows indicate the transfer of two control containers to "0.01 " ppm. 

 Mean total petroleum hydrocarbon concentrations ± s.d. (N) at each nominal 

 concentration were "0.01 " ppm: 0.020 ± 0.008 (9); "0.1 " ppm: 0.082 ±0.044 

 (20). 



146 



