The Deepwater Horizon (DWH) event - the largest marine oil spill in global history - was associated in time with a complex and diverse set of ecosystem changes. Four major “ecotypes” including the open ocean pelagic, deep benthic, continental shelf, and coastal/inshore habitats were affected. Despite nearly 10 years since the event, not all resources have recovered to pre-spill levels and some are projected to take decades to perhaps a century or more to recover. Two major reservoirs of DWH oil remain in the environment (deep benthic and coastal wetlands); in some cases little oil weathering has occurred resulting in ongoing toxic contamination. Although containing a significant proportion of the majority of the Gulf’s biodiversity of fishes and benthos, prior to DWH the deep sea was particularly poorly studied. New information collected post-DWH indicates a widespread decline in mid-water fish and deep-water benthos species. Distribution shifts of open ocean delphinids coincided with the spill.

Continental shelf resources impacted by the spill included many species of commercial and recreational fisheries importance. Shelf communities exhibited moderate to significant declines coincident with the spill. Recovery of shelf resources is complicated by increased lionfish abundance post-spill. Inshore resources (and particularly bottlenose dolphin, American oyster and blue crab) were impacted not only by oil pollution but countermeasures used to mitigate oil impacts, and especially the release of large quantities of fresh water into coastal marshlands. While some inshore resources have recovered, DWH impacts may have weakened the resiliency of some species and communities potentially making them more susceptible to a wide range of ongoing stressors including sea level rise, ocean warming, acidification, chronic toxic exposures and others. Long-term ecosystem remediation programs (e.g., marsh reconstruction) may very well have consequential impacts for a range of ecologically and economically important resources affected by DWH. The oil industry has been steadily moving to deeper waters of the Gulf. In 2018 more than half of Gulf oil was derived from the “ultra-deep” (e.g., > 1,500 m). Thus there is an urgent need to better quantify the productivity and vulnerability of deep sea resources to future oil spills.