A series of experiments in Willapa Bay, Washington, indicates the degree to which the presence of spilled oil modifies the burrowing behavior of infauna and the extent to which they redistribute oil into the sediment. Small amounts of North Slope crude oil introduced at low tide directly into burrow openings (mostly made by the crustacean Callianassa) caused a limited and temporary reduction in the number of burrow openings. The presence of low concentrations of oil to depths of 30 cm shows that the fauna mixed this oil into the sediment. In contrast, a layer of oil-saturated sand < 1 cm thick buried about 5 cm below the sediment surface sharply reduced the number of burrow openings. After a year a few new burrows penetrated only the margins of the experimental plot (e en though chemical studies showed that the oil was biodegraded in 6 months). Cores showed a dramatic reduction in bioturbation under the buried oily sand layer.

The experiments suggest that small amounts of oil temporarily stranded by tides have no long-range effect on burrowing behavior. The fauna, however, are capable of introducing measurable amounts of oil into the subsurface, where it is retained long after the stranded oil has moved elsewhere. A buried layer of oily sand greatly reduced infaunal activity, presumably because

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the oil presents an impenetrable physical barrier that can persist after the oil itself is degraded by bacteria.

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