Recovery of saltmarsh meiofauna six years after the Deepwater Horizon oil spill

We examined the recovery of infauna from the 2010 Deepwater Horizon oil spill in reference, moderately and heavily oiled Louisiana, USA salt marshes. Although density and diversity were severely impacted by the spill initially, total meiofauna, nematodes, copepods, and annelids, excluding the polychaete Manayunkia aestuarina, recovered in about 3 years in near synchrony with Spartina alterniflora stem density. However other common taxa either recovered more slowly (i.e., juvenile bivalves and amphipods) or remained significantly lower in density at oiled compared to reference sites 6 years after the spill. Specifically, M. aestuarina, the tanaid Hargeria rapax, the kinorhynch Echinoderes coulli, ostracods, and juvenile gastropods did not recover at the heavily oiled sites, and M. aestuarina and E. coulli failed to recover at moderately oiled sites. Several factors possibly contributed to slow recovery even after the re-establishment of aboveground vegetation. The concentration of petroleum hydrocarbons (TPH) remained elevated at moderately and heavily oil sites, and the direct toxic effects of oil may have been long lasting for intolerant fauna; the densities of E. coulli and M. aestuarina across all samples were inversely correlated with TPH. In addition, several of the slowly recovering taxa also disperse slowly. Finally, live belowground biomass of roots and rhizomes (a key indicator of sediment quality) remained significantly reduced at heavily and moderately oiled sites, and belowground biomass and the densities of M. aestuarina and juvenile gastropods were positively correlated. We conclude that the factors controlling the rate and intensity of infaunal recovery from the DHOS differed among taxa and over time. The factors that were important later in the recovery process were not dissimilar to those affecting succession following marsh restoration by planting S. alterniflora, and the legacy of oiling from the spill did not greatly slow the recovery of infauna compared to that observed in restored wetlands. At current rates, full recovery of the infaunal community will require about a decade at moderately oiled and longer at heavily oiled sites.