Populations of deep-sea fish, crustaceans and cephalopods in the Gulf of Mexico have declined by nearly 60 per cent to 85 per cent over a short period, with no significant recovery recorded for more than a decade, according to a new study published in the journal Proceedings of the National Academy of Sciences (PNAS).
The study, titled ‘Immense but not immutable: A sudden and sustained decline in deep-pelagic life in a large oceanic ecosystem’, found that the decline began around 2011, shortly after the 2010 Deepwater Horizon oil spill, one of the largest marine oil spills in history.
Researchers identified the spill and the associated mitigation measures as the most plausible explanation for the decline, as they found no natural environmental factors that could account for the changes.
The research examined marine life from the surface to depths of 1,500 metre over a 12.5-year period, using deep-sea net sampling, acoustic surveys and genomic analysis. The findings showed that fish abundance fell by 63.5 per cent, crustaceans by 62 per cent and small cephalopods by 59.7 per cent between the 2011 baseline and subsequent surveys conducted from 2015 to 2023.
Some ecologically important groups recorded even steeper declines. Krill populations fell by 72.8 per cent, bristlemouth fish by 69 per cent and lanternfish by 62.9 per cent. These species play an important role in marine food webs, serving as prey for larger fish, sharks, whales and seabirds.
The researchers also found evidence of declining genetic diversity in two of the three lanternfish species examined. Reduced genetic variation can affect a population’s ability to reproduce, adapt to environmental changes and recover from disturbances.
The study ruled out methodological differences in sampling, changes in water temperature, oxygen levels and food availability as likely explanations. The researchers also found that the decline was independently supported by acoustic measurements of marine life in the water column.
The 2010 Deepwater Horizon disaster released an estimated 4 to 4.9 million barrels of oil into the Gulf over 87 days. Researchers noted that oil residues continued to be detected in deep-sea organisms years after the spill, indicating prolonged exposure.
The decline could have wider ecological consequences. Deep-pelagic animals migrate vertically between deep and surface waters, helping transport carbon to the deep ocean and supporting marine food chains. Their reduced abundance could affect carbon cycling and the availability of prey for larger marine animals.
The researchers said the Gulf’s deep-sea ecosystem appeared to have shifted to a persistently low-abundance state, with its recovery timeline still unknown, pointing at the fact that even vast and relatively remote ocean ecosystems are vulnerable to human-induced disturbances.
