Marine life in the Gulf of Mexico plummeted by about 60% after BP’s 2010 Deepwater Horizon oil spill and has still not fully recovered, according to a new study.
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. According to the study published Monday in PNAS, the disaster – which also killed 11 people and injured 17 others – led to the “sudden, severe and persistent declines in the abundance” of marine life for more than a decade.
Conducted using acoustic sonar, multi-depth trawling nets and genetic studies, the study revealed dramatic population drops across the gulf between 2011 and 2015: fish declined by 63.5%, macrocrustaceans including shrimp and krill fell by 62% – severely affecting a primary food source for whales – 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. They also noted that natural factors like temperature, oxygen and food availability did not vary with the decline, confirming the spill as the primary cause.
The marine species most severely affected were also among the most vital to open-ocean ecosystems and global food webs. Krill, a primary food source for deep-sea fish and shrimp, plunged by 72.8%. Bristlemouths – likely the most abundant backboned animals on Earth – fell by 69%. Meanwhile, 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.
Because large amounts of marine species were instantly killed or affected due to chemicals stored in their eggs, this led to sharp reductions in population sizes, in turn leading to reduced genetic variations, the study found.
Scientists examined genetic diversity in three lanternfish species that suffered severe population crashes, which subsequently led to inbreeding among the survivors.
“The rate of genomic diversity decline is remarkable given the short temporal scale,” the study noted.
The study also examined chemical dispersants applied during the oil spill cleanup. While these agents break oil into smaller droplets, they also spread polycyclic aromatic hydrocarbons (PAHs) – among 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. The study further highlighted that residual oil – even at sublethal concentrations – may have hindered the ability of certain species, including damselfish and stingrays, to locate mates through olfactory cues.
“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,” the study’s lead researcher, Tracey Sutton, a biological oceanographer at Florida’s Nova Southeastern University, said.
“That was the idea [of the dispersants]. 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,” he 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. We need … to be as absolutely careful as can possibly be,” Sutton continued.
Similarly, Pedro A Peres, one of the study’s co-authors and a researcher at Florida International University’s Institute of Environment, said: “Our findings are particularly concerning because these are species that are abundant, widespread and historically might not have been considered vulnerable. What we are seeing suggests that even species that appear abundant can experience substantial changes that may go unnoticed without monitoring.”
Meanwhile, BP spokesperson Paul Takahashi in a statement said: “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 … We have worked hard to build a safer and stronger BP. We have made many changes intended to help prevent an event like this from ever happening again. He added that the company has spent more than $69m for the Gulf region’s recovery.
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 over the spill. The disaster also affected coastal communities in Mexico, which, as of 2020, had yet to receive any compensation. BP has denied that the oil from the spill reached Mexican waters.
