Selected microbial parameters were monitored in sediments from a pristine and an oil-field salt marsh. Although numbers of hydrocarbonoclastic bacteria and fungi were significantly greater in the oil field, the values did not show a strong correlation with levels of hydrocarbons (r = 0.43 and r = 0.49, respectively). However, a high correlation was noted between ratios of hydrocarbonoclastic and total aerobic heterotrophic bacteria and levels of hydrocarbons as well as the relative concentration of hydrocarbons (ratio of hydrocarbons to chloroform extractables) (r = 0.87 and r = 0.77, respectively). Data suggest that this first ratio is a more valid microbial indicator of hydrocarbon abundance than other factors examined. Significant differences in the ratio of pigmented to total colony-forming units, the ratio of different to total colony-forming units, and the diversity index were noted between the natural and oil-field marsh. It is suggested that the presence of hydrocarbons alters the relative abundance of the most predominant aerobic heterotrophic bacteria.
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