More than 16 years after the Deepwater Horizon disaster fouled the Gulf of Mexico, the deep-sea creatures living hundreds to thousands of feet below the surface still haven't bounced back. A new peer-reviewed study finds that populations of deep-water fish, crustaceans and squid declined significantly after the 2010 spill and have yet to recover.
The research, published in the journal PNAS, combined more than 2,000 net samples with acoustic surveys and genetic analyses gathered across more than a decade of fieldwork, according to Florida International University. Researchers analyzed net samples collected between 2011 and 2023 and examined genetic diversity across three lanternfish species to track how the Gulf's hidden ecosystem has shifted since the spill. The team was led by Tracey T. Sutton of Nova Southeastern University and included FIU marine scientists Kevin Boswell, Heather Bracken-Grissom, Marta D'Elia and Pedro A. Peres.
The numbers are stark. FIU reported declines of 64 percent in fish species, 62 percent in large crustaceans and 60 percent in small squid and other cephalopods, while krill fell by nearly 73 percent, lanternfish by 63 percent and bristlemouth fish by 69 percent. The Guardian reported slightly different figures drawn from the same body of research, putting the fish decline at 63.5 percent, macrocrustaceans including shrimp and krill at 62 percent, and cephalopods such as squid and octopus at 59.7 percent between 2011 and 2015.
A Vanishing Food Source for the Gulf's Giants
Dense patches of prey that were common in 2011 have virtually disappeared, the FIU account notes. Those concentrations once served as essential food resources for whales, dolphins, tuna, sharks and seabirds, and their disappearance strikes at the base of the Gulf's deep-water food web.
The affected habitat, known as the deep-scattering layer, extends between 600 and 5,000 feet below the surface and accounts for more than 90 percent of the Gulf's volume, supporting what researchers describe as an extraordinarily rich assemblage of marine life. Deep-water animals in this zone provide food for the Gulf's largest predators and transport carbon from surface waters into the deep ocean — meaning their losses may weaken marine food webs and reduce the ocean's capacity to store carbon.
Ruling Out Other Causes
Researchers ruled out several alternative explanations after accounting for sampling consistency and differences among the Gulf's water masses, finding no corresponding changes in deep-water temperature, oxygen or food availability that could otherwise explain the decline. As reported by NBC News, one researcher put it simply: “None of those vary with the decline. The event that did was the oil spill.” The Guardian's account similarly describes the finding that natural factors like temperature, oxygen and food availability did not vary with the decline as confirming the spill as the primary cause, though the study itself stops short of establishing direct causation — its authors instead identify the Deepwater Horizon spill and its associated response efforts as the most plausible explanation for the timing and scale of the declines.
The 2010 disaster released between 4 million and 4.9 million barrels of oil into the Gulf, and response efforts injected roughly 770,000 gallons of chemical dispersant near the wellhead in an attempt to break up the slick. Oil-related compounds have since been detected in deep-water fish eggs and cephalopod tissue, and researchers note that this kind of contamination can cause mortality, developmental damage and reduced fitness in affected animals — and may even interfere with smell, potentially hampering deep-sea fish from locating mates.
Scientists Describe a Persistent, Uncertain Future
“Genetic diversity is nature’s insurance policy,” said Heather Bracken-Grissom, one of the FIU scientists on the research team. She said it is the foundation for species to adapt and survive, and that its loss reduces evolutionary potential. Kevin Boswell added that the changes measured through independent methods demonstrate significant change in the midwater ecosystem. Pedro A. Peres noted that even abundant, widespread species can undergo substantial changes that may go unnoticed without sustained monitoring.
Sampling since 2015 has shown that the low populations have remained depressed, with a slight rise in 2022 and 2023 that did not prove statistically significant or lasting, per NBC News. The researchers concluded that the Gulf may have entered a persistently depleted ecological state with no clear timeline for recovery. Per WUSF, the team plans to continue tracking the Gulf's recovery, with its next research cruise scheduled for June 2027.
The findings arrive alongside other post-spill research raising similar alarms about the Gulf's top predators. A separate 2024 study examining the region's whales and dolphins found population drops as high as 83 percent, according to the same NBC News report — a reminder that the consequences of the spill have rippled far beyond the wellhead itself, reaching both the smallest prey species and the largest animals that depend on them.
