oil-exposed snails, with one exception (i.e., 6/10/76). After transfer of two 

 control containers to "0.1" ppm, lid deposition decreased and remained 

 suppressed for some 30 days (Figure 1 1-5). In a similar experiment conducted 

 the next spring, control containers were transferred to "0.1" ppm and 

 containers held at "0.1" ppm were transferred to control conditions. Shifts in 

 deposition patterns were again observed (Figure 11-6), although not until after 

 four weeks for the former control group of snails. 



With oyster drills {U. cinerea), there was no demonstrable effect of oU on 

 fecundity when tested by one-way analysis of variance (P > 0.25), nor 

 did exposure to "0.01" ppm and "0.1" ppm have any statistically significant 

 effect on egg capsule placement. Egg capsule deposition behavior of oyster 

 drills was affected by oil, however. No drills held at "0.1" ppm deposited 

 capsules on the undersides of the container lids, in contrast to 13% to 14% lid 

 deposition in 0.01 ppm and control treatments, respectively (Table 11-5). 



Larval Growth 



The influence of No. 2 fuel oil (WAF) on larval growth of three invertebrate 

 species is summarized in Table 1 1 -6. Growth of A', obsoletus larvae (jum shell 

 length) was dramatically impaired at "0.01" ppm and "1.0" ppm, but was only 

 slightly reduced at "0.1" ppm. This curious response pattern was observed in 

 two experiments involving different hatches of larvae. In contrast, the effect of 

 oil on larval growth of C fomicata correlated positively with increasing oil 

 concentration in the static experiments. Reduced growth was also evident at 

 "0.1" ppm in the single flow-through experiment conducted. Growth of C 

 inoratus larvae, measured as change in mean dry weight /individual, declined 

 relative to controls as development proceeded at the "0.1" ppm concentration. 

 The dry weight of oil-exposed larvae was only 70.1 percent of control weight 

 for the Stage IV zoea, and only 63 percent of control weight for the Stage V 

 zoea. However, these same C inoratus larvae exhibited no differences in 

 molting frequency or in carapace length with respect to control individuals. 

 Cancer irroratus larvae in all sublethal oil treatments (i.e., all below "1 .0" ppm) 

 reached the megalops stage in 25-28 days. 



DISCUSSION 



The concentration of hydrocarbons lethal to larvae is generally believed to 

 be about one-tenth of the concentration lethal to adults (14, 21). In our study, 

 a nominal concentration of 1.0 ppm was lethal to adults and larvae alike, 

 although 50% mortality of larval N. obsoletus occurred much sooner for larvae 

 than for adults. Exposure to "0.01" ppm and "0.1" ppm produced mainly 

 sublethal effects in both larvae and adults of this species. 



149 



