FISHERY BULLETIN: VOL. 79, NO. 4 



Table 2.— Percentage of Dungeness crabs detecting the clam extract (FDCE) after exposure to continuously flowing seawater 



contaminated with Prudhoe Bay crude oil. 



After 24- h exposure 



FDCE 



(g/i) 



Treatment 



No. Detecting 

 tested (%) 



After 24 fi in clean water 



No. Detecting 

 tested (%) \^ 



After 48 h in clean water 



No. Detecting 

 tested (%) 



\ 



16.0 0.999 



3.46 .937 



.40 .473 



1.18 0.723 

 .05 .177 

 .13 .282 



1.96 838 

 106 697 

 197 840 



Percentage of Dungeness crabs probing with the chelae upon presentation of a clam extract (FDCE) after exposure 



2.18 0.860 

 ,329 .434 

 924 .664 



0.114 0.265 

 ,395 .470 

 .793 .627 



2.20 0.862 

 102 687 



1.10 .705 



Table 4. — Percentage of Dungeness crabs responding to a clam 

 extract (FDCE) presented in clean water 1 h after 24-h exposure 

 to oil-contaminated seawater. 



FDCE 



(g/i) 



Treat- 

 ment 



No. 

 tested 



Crabs detecting Crabs cfielae probing 



10- 



10" 



Control 



0.002 0.040 



.551 



.681 



.542 



.591 



89 

 80 

 

 3 

 

 



0.952 0.671 



1.118 



.710 



antennular flicking was not affected by expo- 

 sure. The antennular flicking rate during the 

 minute before introduction of the clam extract 

 did not vary under exposure, control or recovery 

 conditions over both experiments (median test, 

 X^ = 2.62, df = 7, P = 0.08). The overall grand 

 median flicking rate was 33 flicks/min ( n = 653). 

 The median antennular flicking rate for resting 

 Dungeness crabs was previously found to be 30 

 flicks/min (Pearson et al. 1979). 



DISCUSSION 



Whereas our exposure regime was low, brief, 

 and well-characterized compared with most of the 

 oil effects studies to date, we must clarify the 

 circumstances to which our exposure is applicable. 

 We exposed Dungeness crabs for 24 h to oil- 

 contaminated seawater (0.27 ppm total hydro- 

 carbons by IR) in which dissolved monoaromatic 

 hydrocarbons (0.247 ppm) predominated. Our sys- 

 tem produced this oil-contaminated seawater by 



continuous mixing of fresh oil with flowing sea- 

 water (9° C) followed by separation of floating 

 oil and diversion of nonfloating mixture to the 

 exposure chambers (Vanderhorst et al. 1977). 



For a study of its kind we believe our exposure 

 regime to be the best characterized to date, but the 

 exposure regime is not representative of all, or 

 perhaps even most, oil spill situations. Concentra- 

 tions of total oil in the water ranging from 0.1 

 to 1.0 and lasting several days have indeed been 

 reported (Grahl-Nielsen 1978; Calder and Boehm 

 in press), but in such cases detection of substantial 

 amounts of alkane (saturate) hydrocarbons indi- 

 cated that an unknown but substantial amount 

 of oil was emulsified, i.e., present as droplets. 

 Because only 27( of the total hydrocarbons in 

 our oil-contaminated seawater were saturates 

 (Anderson et al. 1980), our exposure regime did 

 not mimic situations where emulsified oil and 

 high proportions of saturate hydrocarbons exist. 

 The chemosensory effects of emulsified oil remain 

 to be studied. Our results are most applicable to 

 situations where dissolved monoaromatic hydro- 

 carbons predominate in the water column. 



When oil is spilled, monoaromatic hydrocarbons 

 usually do not attain high concentrations in the 

 water column but rather are rapidly lost by 

 evaporation (McAuliffe 1977a, b). During the last 

 3 d of a 21-d platform spill in the Gulf of Mexico 

 McAuliffe et al. (1975) measured total low molec- 

 ular weight (Ci-Cg) hydrocarbons in the water 

 column using a gas equilibration method similar 



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