FISHERY BULLETIN: VOL. 79, NO. 4 



our behavioral results indicate direct structural 

 damage to chemosensory cells was unlikely, 

 which of the other mechanisms actually produced 

 the observed chemosensory impairment remains 

 an open question. 



Decapod crustaceans have two chemoreceptor 

 systems, one seated in the antennules and another 

 in the dactyls, chelae, and mouth parts (Luther 

 1930; Case and Gwilliam 1961; Levandowsky and 

 Hodgson 1965; Hazlett 1968, 1971a, b). The obser- 

 vation that after presentation with a clam extract 

 a significant proportion of exposed crabs showed 

 chelae probing without the normally preceding 

 increase in antennular flicking suggests that 

 24-h exposure to our oil-contaminated seawater 

 depressed the functioning of the antennular sys- 

 tem in Dungeness crabs while, at least as far 

 as we can determine, not significantly affecting 

 the dactyl chemoreceptor system. Perhaps longer 

 exposure would have affected the dactyl system. 



The practical implication that needs further 

 investigation is how the observed impairment of 

 the chemosensory antennular flicking response 

 would affect food foraging by the Dungeness crab. 

 Whereas the exact role of the antennules in food 

 finding is not fully understood, abundant evidence 

 exists for the involvement of the antennules 

 in food searching. Upon water-borne chemical 

 stimulation, increases in antennular flicking 

 rate precede food searching behaviors in the 

 Dungeness crab (Pearson et al. 1979) and the blue 

 crab (Pearson and 011a 1977). Because the electro- 

 physiological work of Schmitt and Ache (1979) 

 demonstrated that antennular flicking enhances 

 perception of changes in the chemical milieu, 

 increased flicking would presumably further 

 enhance detection of rapid chemical changes. 

 In the spiny lobster, Panulirus argus, chemical 

 stimulation of the antennules usually initiated 

 feeding behavior although chemical-tactile stimu- 

 lation of the dactyl was more effective (Maynard 

 and Sallee 1970). In hermit crabs intact anten- 

 nules were necessary to sustain feeding behavior 

 when contact with food is not direct and immedi- 

 ate (Hazlett 1968). Ablation of the antennules 

 impaired the ability of the pelagic shrimp, Acetes 

 sibogae australis, to follow food scent trails 

 although antennular ablation did not prevent the 

 detection of scent trails (Hamner and Hamner 

 1977). The ablation experiments of Reeder and 

 Ache (1980) showed that chemosensory input from 

 the lateral aesthetasc hair tufts of the antennules 

 triggers food searching by P. argus and guides 



the spiny lobster to a distant odor source. Our 

 observation of an impaired chemosensory anten- 

 nular flicking response coupled with the good 

 evidence of antennular involvement in food find- 

 ing indicated that difficulty in finding food in 

 the presence of petroleum hydrocarbons is a possi- 

 bility for Dungeness crabs. If the antennular 

 chemoreceptor system is as critical to successful 

 guidance to distant odor sources in the Dungeness 

 crab as the results of Reeder and Ache (1980) 

 showed it is for the spiny lobster, then we par- 

 ticularly need to investigate whether entry to 

 baited traps is affected when dissolved aromatic 

 or other hydrocarbons are present. 



ACKNOWLEDGMENTS 



This work was supported by the National 

 Oceanic and Atmospheric Administration of the 

 U.S. Department of Commerce under the Inter- 

 agency Energy-Environment Program of the U.S. 

 Environmental Protection Agency. 



We thank J. W. Anderson for his valuable 

 discussions. Chemical analyses were performed 

 by J. W. Blaylock and J. Webster. 



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