Recovery of Saltmarsh Macroinfauna After the Deepwater Horizon Oil Spill

Abstract To examine invertebrate community recovery after the 2010 Deepwater Horizon oil spill, we monitored the recovery of macroinfauna in replicated reference, moderately and heavily oiled salt marshes in Barataria Bay Louisiana for 8.5 years after the spill. Plants suffered near 100% mortality in heavily oiled marshes, profoundly altering the sedimentary environment. Plants in moderately oiled marshes did not suffer extensive mortality but experienced reduced above- and belowground plant biomass. A community analysis based on 40 macroinfaunal taxa was conducted during early (2011–2012), middle (2013–2017), and late (2017–2018) stages of recovery. The early stage was marked by very low taxonomic diversity (< 1–4 taxa per sample) and low total macroinfaunal abundance (0– < 8000 m −2 ) across all marshes, while the middle stage was denoted by relatively high diversity (7–8 taxa per sample) and very high abundances in heavily oiled marshes where densities exceeded reference and regional means by factors of 4–5. The community in the heavily oiled marshes diverged from reference and moderately oiled marshes during the middle recovery period when the crustaceans Apocorophium louisianum and Leptochelia rapax , the polychaete Alitta succinea , and oligochaetes dramatically increased in abundance, while at the same time, abundance increases of the polychaetes Manayunkia aestuarina , Streblospio gynobrachiata , and Capitellidae sp. lagged behind increasing trends at reference and moderately oiled sites. Macroinfaunal community similarity in moderately oiled marshes differed from reference and heavily oiled marshes in the middle recovery stage but did not differ from reference sites the during late recovery stage. Heavily oiled community similarity not only differed from moderately oiled and reference marshes in all three recovery stages but remained different from reference sites on the last collection date. These observations indicate that moderately oiled marshes recovered by about 8 years, but that heavily oiled marshes will likely require more than a decade to reach equivalency with reference sites.