Effects of oiled sediment on predation on the littleneck clam, Protothaca staminea, by the Dungeness crab, Cancer magister

Field and laboratory experiments examined how oiled sediment influenced predation on littleneck clams, Protothaca staminea, by Dungeness crabs, Cancer magister. In two field enclosure experiments lasting 13 and 29 days crabs consumed more clams from oiled than clean sand. Clams were shallower in oiled than clean sand. To test whether the observed increase in predation rate on clams from oiled sand was due to shallow burial, a 19-day laboratory experiment examined predation rates on clams buried in different depths of sand. The high consumption of clams from shallow-clean sand indicated that shallow burial could have accounted for most but not all the higher consumption of clams in oiled sand. In a second laboratory experiment without crabs, clams were again shallower in oiled than clean sand. Clams did not actively emerge from oiled sand but did burrow slower into oiled sand. Shallow burial and slow reburrowing in oiled sand led to increased predation of littleneck clams through increasing the accessibility of clams to Dungeness crabs.