port how antennular behavior was used to deter- 

 mine the concentrations at which the Dungeness 

 crab, Cancer magister (Dana), detected petroleum 

 hydrocarbons. 



For decapod crustaceans the antennules have 

 been considered the site of distance chemorecep- 

 tion (Hazlett 1971), and their flicking may be 

 analogous to sniffing in vertebrates (Fuzessery 

 1978). Previous work has shown that in the blue 

 crab, Callinectes sapidus, the antennular behavior 

 indicating detection of food substances (Pearson 

 and 011a 1977) also indicated detection of the 

 petroleum hydrocarbon naphthalene ( Pearson and 

 011a 1979, 1980) and the water soluble fraction 

 of crude oil (Pearson et al. in press). In the 

 Dungeness crab, similar antennular behavior, 

 i.e., a change in orientation and increased flicking 

 rate, also indicated detection of food substances 

 (Pearson et al. 1979). Here we used these changes 

 in antennular behavior to determine chemosen- 

 sory detection thresholds in the Dungeness crab 

 for naphthalene and the water soluble fraction 

 (WSF) of Prudhoe Bay crude oil. 



Materials and Methods 



Dungeness crabs, trapped in the Strait of Juan 

 de Fuca, Wash., were held outdoors in 1,200 1 

 tanks under the conditions described by Pearson 

 et al. (1979). The seawater temperatures (± SD) 

 during the naphthalene and WSF experiments 

 were 12.7°±0.6° C and 10.6°±0.3° C; the salin- 

 ities, 31.6 ±0.91, and 32.0±0.0'L; the dissolved 

 oxygen, 6.9 + 0.7 mg/1 and 7.3 ±0.5 mg/1; and the 

 pH, 8.12 ± 0.17 and 8.02 ± 0.16. 



Experimental Solutions 



Saturated solutions of naphthalene were pre- 

 pared by adding naphthalene crystals to seawater 

 filtered through a 0.4 /xm Nucleopore^ membrane. 

 These stock solutions were stirred continuously at 

 room temperature on a magnetic stirrer and were 

 used after at least 18 h of stirring and no more than 

 5 d from first use. On each day of testing, a portion 

 of the stock solution was siphoned off and passed 

 through a 100 ml glass syringe fitted with a 

 Millipore prefilter (Type A025) to remove any 

 naphthalene crystals. Less than 1 h before testing, 



The use of trademarks does not imply endorsement by 

 National Marine Fisheries Service, NOAA or Battelle, Pacific 

 Northwest Laboratories. 



serial dilutions of this filtered stock naphthalene 

 solution were made with seawater freshly filtered 

 through a 0.4 ^tm membrane. An aliquot of the 

 filtered seawater used for dilution served as the 

 control solution. Experimental and control solu- 

 tions were kept in a water bath at ambient 

 seawater temperature during testing. 



On each day of testing, samples of the stock 

 solution and 10 ~^ dilution were analyzed for 

 naphthalene content. Ten milliliters of hexane 

 were vigorously shaken with 50 ml of sample 

 solution for 1 min. This hexane was removed and 

 analyzed for naphthalene content by capillary GC 

 methods (Bean et al. 1978). The stock naphthalene 

 solution was 22.9±2.1 mg/1, and the 10~^ dilution 

 was 2. 2± 0.2 mg/1. 



The WSF of Prudhoe Bay crude oil was prepared 

 freshly each day by methods similar to Anderson 

 et al. (1974). In a 19 1 glass bottle, one part oil was 

 gently poured over nine parts membrane-filtered 

 seawater. Before the oil was added, a glass siphon 

 tube inserted through a stopper covered with 

 aluminum foil was placed in the filtered seawater. 

 With the bottle stoppered, the seawater was slowly 

 stirred on a magnetic stirrer for 20 h at room 

 temperature. The stirring speed was adjusted so 

 that the vortex did not extend more than 25% of 

 the distance to the bottom of the bottle. After 

 mixing, the oil and water phases were allowed to 

 separate for 1 h. The water phase was then 

 siphoned from below the oil phase and filtered 

 through a prefilter under very low pressure to 

 remove any remaining oil droplets. Serial dilu- 

 tions of the resulting WSF were then immediately 

 made with freshly membrane-filtered seawater 

 and kept in a water bath at ambient seawater 

 temperature during use. The membrane-filtered 

 seawater used for dilution was the control solu- 

 tion. The stock WSF was analyzed by capillary gas 

 chromatography for diaromatic and triaromatic 

 hydrocarbons (Bean et al. 1978), and by gas 

 partitioning analysis modified from McAuliffe 

 (1971) for monoaromatics. 



Chemosensory Threshold Determination 



The apparatus and procedures of Pearson et al. 

 (1979) were used here. In brief, glass testing 

 chambers were arranged on four trays, 10 cham- 

 bers to a tray, and the trays were surrounded by 

 blinds. The experimental solutions were intro- 

 duced into each testing chamber through an inlet 

 manifold connected to a glass funnel. Seawater 



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