PEARSON ET AL.: CHEMOSENSORY ANTENNULAR FLICKING RESPONSE 



to ours and found concentrations ranging from 

 0.002 to 0.010 ppm at 5 and 10 m. Near-surface 

 concentrations ranged from a maximum of 0.200 

 ppm near the platform (230 m) to 0.002 ppm at a 

 distance (1.5 km). About half these C1-C9 hydro- 

 carbons, i.e., 0.100 ppm, were the monoaromatics 

 predominating in our oil-contaminated seawater. 

 During four 10.5-barrel experimental spills con- 

 centrations of C2-C10 aromatic hydrocarbons 

 ranged from 0.002 to 0.050 ppm at 1.5 m within 20 

 min after the spill and were not detectable after 1 h 

 (McAuliffe 1977b). Because the low temperature 

 (9° C) of our seawater and perhaps other system 

 properties slow evaporative loss, our system pro- 

 duced oil-contaminated seawater with a mono- 

 aromatic concentration 2.5 to 5 times higher than 

 those reported in the water column during spills. 

 While our higher concentration has not been 

 reported, it is conceivable that subsurface leak- 

 age of fresh oil from pipelines or sunken vessels 

 into cold water could produce exposures similar 

 to ours. 



One example of how cold temperature and other 

 hydrographic conditions may combine to prevent 

 evaporative loss and allow monoaromatic concen- 

 trations more persistent and higher than those 

 cited above for oil spills is found in Valdez Arm, 

 Alaska. Because of the stratification of the water 

 column typical of a fjord, effluent from the oil 

 tanker ballast water treatment facility at Valdez 

 does not mix uniformly but instead is confined to a 

 lens near the bottom. The treatment facility 

 releases about 4.5 x lOM (12 x 10^ gal) daily 

 (Lysyj et al. 1979) with average concentrations of 

 monoaromatic hydrocarbons between 5.1 and 6.4 

 ppm (Lysyj et al. 1979, 1981; Rice et al. 1981). The 

 distribution of monoaromatics in the receiving 

 body was studied by Lysyj et al. (1981) who 

 found the monoaromatics trapped within a narrow 

 ( 10 m) zone of maximum concentration that spread 

 horizontally 2 to 3 km in a thin pancake shape. 

 Depth of the pancake varied with season from 

 50 to 65 m and approached the bottom. A mono- 

 aromatic concentration of 0.021 ppm was found 

 2 m off the bottom, and the maximum mono- 

 aromatic concentration observed was 0.127 ppm, 

 half of the exposure concentration used here. 

 Our exposure regime then may be most applicable 

 to situations where there is chronic release of 

 monoaromatic hydrocarbons under hydrographic 

 conditions, e.g., low temperatures and stratifi- 

 cation of the water column, that prevent evapora- 

 tive loss. 



The observed chemosensory impairment under 

 oil exposure could have derived from several pos- 

 sible mechanisms, structural damage to chemo- 

 receptor cells, anesthesia of chemoreceptors or 

 other neurons, masking of food cue odor by oil, 

 oil-induced changes in motivation, or coating 

 or matting of the sensory hairs of the antennule 

 by oil. The rapid recovery of the antennular flick- 

 ing response eliminates only direct structural 

 damage to the chemoreceptor cells as a possibility. 

 Cellular damage would have required a recov- 

 ery period of days whereas other mechanisms, 

 such as masking or anesthesia, would have been 

 rapidly reversible upon return to clean seawater 

 (Johnson 1977). Anesthesia of the chemoreceptor 

 or higher level neurons remains possible because 

 our oil-contaminated seawater contained several 

 aromatic and saturate hydrocarbons known to 

 produce anesthesia or reversible narcosis in 

 barnacle larvae (Crisp et al. 1967). Dungeness 

 crabs do detect the water-soluble fraction of 

 Prudhoe Bay crude oil at 10 "* ppm (Pearson et al. 

 1980) so that masking of the clam extract by the 

 odor of oil was also possible. Odor masking by oil 

 was also suggested by Atema and Stein (1974) as 

 one possible mechanism behind a longer food 

 finding time in the northern lobster, Homarus 

 americanus. A change in feeding motivation was 

 also suggested by Atema and Stein, but the 

 observation in our first experiment of no differ- 

 ence between exposed and control conditions in 

 the proportion of Dungeness crabs showing the 

 chelae probing indicative of food searching argues 

 against a change in motivation having occurred 

 here. Antennular flicking enhances the ability of 

 crustaceans to detect changes in the chemical 

 milieu by splaying out the sensory hairs and 

 increasing the passage of stimulative chemicals to 

 the sensory neurons (Schmitt and Ache 1979), and 

 oil might impair chemosensory function by slow- 

 ing the passage of stimulating chemicals through 

 coating or matting of the sensory hairs. Because 

 our system produced oil-contaminated seawater 

 with only 2% saturate hydrocarbons (Anderson et 

 al. 1980) and thus little oil existed as emulsified 

 droplets rather than dissolved hydrocarbons, we 

 feel that in our system coating of the sensory 

 hairs was not as likely as one of the other 

 mechanisms. In a spill like the Amoco Cadiz 

 where large amounts of oil are emulsified by 

 turbulence (Calder and Boehm in press) physical 

 blockage of chemical cues by the coating of sensory 

 hairs is a possibility that needs study. Whereas 



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