Marine life in the Gulf of Mexico has still not fully recovered from BP's 2010 Deepwater Horizon oil spill, with populations having plummeted by about 60% after the disaster, according to a study published Monday in PNAS. The April 2010 explosion of an offshore drilling unit 50 miles off the Louisiana coast triggered the largest marine oil spill in history, releasing 134m gallons of oil into the ocean and killing 11 people while injuring 17 others. The study, conducted using acoustic sonar, multi-depth trawling nets and genetic studies, revealed dramatic population drops across the gulf between 2011 and 2015: fish declined by 63.5%, macrocrustaceans including shrimp and krill fell by 62%, and cephalopods such as squid and octopus dropped by 59.7%. Researchers found that the post-spill population crash outpaced any decline recorded in similar waters over the past 60 years.
The species most severely affected were among the most vital to marine ecosystems and food webs. Krill, a primary food source for deep-sea fish and whales, plunged by 72.8%. Bristlemouths, likely the most abundant backboned animals on Earth, fell by 69%, while lanternfishes, which sustain seabirds, dolphins, sharks and commercial fisheries, dropped by 62.9%. A 2023 survey of the area found that many of these populations have not recovered sustainably. The study found that large amounts of marine species were instantly killed or affected due to chemicals stored in their eggs, leading to sharp reductions in population sizes and reduced genetic variations. Scientists examined genetic diversity in three lanternfish species that suffered severe population crashes, which subsequently led to inbreeding among the survivors, with the study noting that the rate of genomic diversity decline was remarkable given the short temporal scale.
Chemical dispersants applied during cleanup also contributed to ongoing damage. While these agents break oil into smaller droplets, they also spread polycyclic aromatic hydrocarbons (PAHs) - crude oil's most toxic components - deep into the water column, increasing toxicity exposure for mid-water and deep-sea marine life. Six years after the spill, researchers found elevated levels of PAHs in deep-sea fish eggs and cephalopod tissues, which severely impaired reproduction. Residual oil at sublethal concentrations may have hindered the ability of certain species including damselfish and stingrays to locate mates through olfactory cues.
Tracey Sutton, the study's lead researcher and biological oceanographer at Nova Southeastern University, explained the tradeoff of using dispersants: "If you keep the oil from coming to the surface, then it won't be affecting as many shallow water animals or humans that were there to work on the spill. What that tends to do is break up the oil into smaller droplets, which allowed it to stay deep in the water column. So that probably was not a good thing for these deep pelagic things that we work on, because now you've got this kind of minefield of small oil-laden particles floating around and staying at depth instead of coming to the surface." Sutton added: "We need to consider the deep ocean to be a very fragile system, not this thing that is so large we can't disturb it."
In 2015, BP agreed to pay a record $18.7bn in penalties and damages after the US justice department and four states sued the company. BP said it has spent more than $69m for the Gulf region's recovery. A BP spokesperson stated: "We will never forget the 11 people who lost their lives. Sixteen years later, we remain keenly aware that we must always put safety first." The disaster also affected coastal communities in Mexico, which as of 2020 had yet to receive any compensation, with BP denying that oil from the spill reached Mexican waters. Since the spill, thousands of people have also filed lawsuits over long-term health problems they attribute to cleanup efforts, with research linking exposure to the spill with increased cancer risks, higher rates of chronic respiratory conditions, heart disease, headaches, memory loss and blurred vision.