Deepwater Horizon Spill Linked to Lasting Declines in Gulf Twilight-Zone Marine Life

The damage reached deep into the Gulf’s food web

The striking result is how broadly marine life declined in the Gulf’s twilight zone after the 2010 Deepwater Horizon disaster. A study published Monday in

PNAS found that, by 2015, fish counts in the affected area were down 63.5% from 2011. Crustaceans such as shrimp and krill had fallen 62%, while squid and octopuses were down 59.7%. The BP-operated well failed and released 134 million gallons of oil; the explosion and spill are described here, with details on the failed well here. The decline has persisted. Researchers sampled the same Gulf location in 2011 and again three and a half years later, using nets at six depths and acoustic sonar to survey waters from the surface to 5,000 feet (1,500 meters). Their later counts were only one-quarter to one-third of the earlier levels. Lead author Tracey Sutton, a biological oceanographer at Nova Southeastern University, said the team examined temperature, oxygen and food supply, but found those variables did not track the drop. The spill’s timing did. Sutton said the evidence points to the oil spill as the most likely cause, while acknowledging the team could not prove a direct causal link. Follow-up sampling through 2015 and beyond found the populations stayed low. A modest uptick in 2022 and 2023 was neither statistically significant nor sustained. That lack of recovery is more consequential than a single post-spill snapshot.

Evidence points to lasting harm

Sutton’s team drew on three kinds of evidence: animals caught in nets, sonar readings and genetic analysis indicating declining diversity associated with inbreeding. Sutton said many animals died soon after the explosion, which killed 11 workers, and during nearly five months of oil and gas leaks. Contaminants were also stored in survivors’ eggs, he said, leaving later generations weaker and more compromised. The losses hit species that anchor the food web. Krill numbers fell 72%, Sutton reported. Lanternfish, recognizable by blue-green lights along their bodies, were down to about a third of their former abundance. Dragonfish, with sharp teeth, light-producing organs and a lure on the head, also suffered major declines. These small and mid-sized animals feed many larger species, including whales and dolphins, so their losses can reshape the wider community. Study co-author Isabel Romero, a chemical oceanographer at the University of South Carolina, said oil and cleanup dispersants harmed fish in different ways. Oil is more toxic overall, while dispersants break it into smaller droplets that can expose animals deeper in the water column. Former National Science Foundation Director Rita Colwell, a University of Maryland environmental microbiologist who led a 10-year, $500 million BP-funded spill research program, said dispersants caused serious problems. She argued that future responses should avoid them and consider agents that encourage oil-consuming microbes. BP spokesperson Paul Takahashi said the accident “forever changed” the company and that BP had made changes intended to prevent a similar event.

A connected ecosystem that remains poorly understood

The research also changes how scientists describe the Gulf’s midwater ecosystem. Sutton said animals move between depths: some surface predators dive, while deep-water species rise at night. The ocean therefore behaves as a connected, pulsing system, rather than a set of isolated layers. The area had not been studied before the 2010 spill, leaving researchers without a pre-spill baseline. That gap matters. Scripps Institution of Oceanography marine scientist Kaitlin Frasier, who was not involved in the study, said scientists know more about space in some ways than the inner ocean. She warned that areas people cannot see are too easily assumed to be healthy, despite the evidence of serious damage. Frasier’s own 2024 study of Gulf whales and dolphins found population declines of as much as 83%. Dalhousie University marine scientist Boris Worm, also not involved in the research, said a single drilling-rig failure caused extensive damage across thousands of square kilometers, with little visible recovery more than 13 years later. Worm and Colwell said the spill’s effects should inform debate over deep-sea mining and expanded deep-water oil drilling. The study cannot settle every question about cause, but its long record of low populations makes the costs of disturbing poorly monitored waters hard to dismiss. The Associated Press says its climate and environmental coverage receives financial support from private foundations, while AP retains responsibility for its content. Its standards for working with outside groups, supporter list and funded coverage areas are available at AP.org.