The behavior of Dungeness crabs, Cancer magister, was observed to determine not only whether oil exposure produced behavioral effects, but also whether crabs could change their behavior to mitigate any exposure effects. Dungeness crabs clearly detected the presence of petroleum hydrocarbons but did not avoid oil under all circumstances. The effects of oil exposure on chemoreception and feeding behavior in Dungeness crabs were determined after measuring the high sensitivity of the crabs to chemical food cues. After 24 h of continuous exposure to 0.3 mg/l of oil-contaminated water, the proportion of crabs showing changes in antennular behavior was significantly reduced. Within 1 hour after return to clean water the antennular response recovered. Field and laboratory experiments then examined how oiled sediment influenced predation on littleneck clams by Dungeness crabs. In field enclosures, crabs consumed more clams from oiled than clean sand. The potential difficulty in finding food due to chemosensory disruption by petroleum hydrocarbons was apparently offset by an oilinduced, change in prey behavior. To the extent that oiled sediment renders prey species more vulnerable to crab predation and crabs switch prey, harvesting of vulnerable prey by crabs would reduce their representation in the benthic fauna and produce ecological effects far different than those predicted from a series of conventional toxicity tests.

"July 1981." "EPA-600/7-81-093." Includes bibliographical references (pages 64-71).