Three large transite-sided enclosures, constructed in a tidal salt marsh in southeastern Virginia, were utilized to evaluate the effects of crude oil spillage on selected microbial populations. Unweathered Louisiana crude oil was spilled in one enclosure, artificially weathered South Louisiana crude in another, and the third served as a control. Each enclosure was constructed so as to allow unhampered exchange with tidal flow on the tidal creek side.

Heterotrophic bacteria and fungi, chitinolytic, cellulytic and petroleum-degrading bacterial populations from the tidal creek, and sediments in intertidal, mid- and back-marsh zones were enumerated at selected intervals following the oil spills. Dominant petroleum-degrading and heterotrophic bacterial isolates were selected for taxonomic grouping.

Within several days following the spills, the levels of petroleum-degrading bacteria rose by several orders of magnitude relative to the control enclosure. This differential has been maintained for approximately one year. Plots of the ratio of oil-degrading to heterotrophic bacteria reveal enhancement of the petroleum degrading component of the heterotrophic population. Mean levels of chitinolytic, cellulytic, heterotrophic bacteria and fungi were not statistically different in the oil and control enclosures. The potential significance of these observations is discussed.

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