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 11-5). 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 ( Ucinerea ), there was no demonstrable effect of oil 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 11-6. Growth of N. obsoletus larvae (jam 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. fornicata 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. 
irroratus 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. irroratus 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. 
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