A Macroinfaunal Ecosystem Engineer May Facilitate Recovery of Benthic Invertebrates and Accompanying Ecosystem Services After an Oil Spill

Knowledge of the ecological mechanisms that influence recovery after oil spills is needed to better manage, mitigate, and restore impacted ecosystems, but the species interactions responsible for these mechanisms are poorly known. Here, we report on a species interaction in the aftermath of the Deepwater Horizon (DwH) oil spill that may facilitate biotic recovery. Although macroinfauna were extirpated in heavily oiled salt marshes after the DwH, amphipods recovered by 4.5 years, and maintained elevated densities, up to 20 × higher, compared to reference sites for 2 years thereafter. Many invertebrates were recovering during this period, and we compared the densities of 10 taxa with the density of amphipods to ask if recovery may have been affected by the abundance of amphipods. Correlation analysis revealed that copepod species richness and the densities of the polychaete Manayunkia aestuarina , ostracods, the kinorhynch Echinoderes coulii , and juvenile gastropods were unrelated to amphipod density. However, the densities of nematodes, copepods (adults and larvae), the tanaid Hargeria rapax , juvenile bivalves, and juvenile polychaetes were positively correlated with amphipod abundance. More than 90% of the amphipods were Apocorophium louisianum . Studies with closely related species indicate that this species is a burrowing and bioturbating ecosystem engineer that grazes benthic microalgae. We hypothesize that amphipod grazing increased the supply and/or availability of microalgae to surface- and suspension-feeding invertebrates either by stimulating microalgal primary production or by suspending microalgal particles, or both. The high abundance of amphipods may therefore have enhanced the resilience of, and ecological benefits provided by, many benthic invertebrates in heavily oiled marshes undergoing ecosystem recovery.