Though the effects of anthropogenic disturbances on coastal marsh plant communities have been extensively studied, responses of marsh soil microbiota to severe disturbance are not well understood. Over 1000 miles of shoreline across the northern Gulf of Mexico were oiled because of the 2010 Deepwater Horizon spill, with the Louisiana coast sustaining the heaviest oiling. Work done in 2011 and 2012 associated changes in salt marsh soil microbial communities with the abundance of hydrocarbons present in the soil. However, few studies have addressed fungal communities in addition to prokaryote communities, or continued into 2013.
In the winter, summer and fall of 2013, we sampled soil at a heavily-oiled and a lightly-oiled salt marsh in Southern Louisiana to understand progressive changes in soil microbial communities and residual hydrocarbons. We sequenced ribosomal DNA to profile the prokaryote and fungal communities of the soil and quantified abundance of polycyclic aromatic hydrocarbons (PAHs) to examine whether PAH abundance corresponded to changes in diversity and community composition. We hypothesized that the increased presence of PAHs drives communities to be more homogenous and less diverse.
Results/Conclusions
We predicted that the heavily-oiled marsh would harbor more depauperate, homogenous communities than the lightly-oiled marsh. We also expected communities to converge through time as oil decayed and natural drivers of salt marsh communities overpowered the influence of the oil. However, we found that the abundance of PAHs only weakly correlated to changes in community composition within bacterial communities, but not fungal communities, and did not explain differences between sites or sampling times. Diversity and community composition of our two sites remained significantly different for both prokaryotes and fungi at, and between, each sampling period. Contrary to our predictions, communities were more heterogeneous at the heavily-oiled site, a result we believe is due to environmental variability interacting with a patchy distribution of oil. Three years after the oil spill, it appears that local variation within each salt marsh was swamping effects that oil might have had on microbial communities. Further work is underway that aims to determine whether differences in soil microbial communities affect plant microbial associates, and the extent to which interactions between the oil, plant and microbial community explain variability in microbial community composition.