Naked amoebas and bacteria in an oil-impacted salt marsh community

Populations of soil amoebas were monitored in two salt marshes in Staten Island, NY for 2 years. One site, Gulfport Reach on the Arthur Kill, has been highly impacted by numerous oil spills. In particular, in 1990 a massive no. 2 fuel oil spill from a ruptured pipe flooded the area; its sediments had total petroleum hydrocarbon (TPH) concentrations in the range 800-46,000 ppm. A reference site I I km away, on the Atlantic coast, had low TPH levels. Amoeba population densities were in general higher in the impacted sediments. In laboratory microcosm experiments, sediment samples from unimpacted sites were treated with added fresh (unweathered) hydrocarbons (no. 2 fuel oil) and cultured; these also yielded higher amoeba numbers than untreated controls. Four distinct amoeba morphotypes were monitored. Changes in population levels of total amoebas were correlated in the two sites, particularly for morphotype 2 (r = 0.83). The ratios of total amoebas to total bacterial numbers were also correlated (r = 0.85) between the sites. This suggests the amoebas may function as generalists, and that their trophic relation to bacterial prey is not much affected by the presence of petroleum hydrocarbons, but rather may reflect regional parameters such as ambient temperature or other physical factors.