Oil Spills Wreak Havoc on the Bottom of the Ocean, Even a Decade Later

A series of studies since the spill have shown a wide range of toxic effects on marine organisms, from impaired development and reproduction to increased mortality and lasting health problems in dolphins and whales. The new paper suggests that lingering pollutants may interfere with some species’ ability to find mates in the dark by disrupting their highly developed sense of smell.

The impacts continue to ripple through the ecosystem, said lead author Tracey Sutton, a professor of marine and environmental sciences at Nova Southeastern University in Florida. A 2024 study found an 80 percent decline in deep-diving toothed whales, he said.

“We used to have a big resident population of sperm whales right off the Mississippi River, but we haven’t seen a sperm whale in 10 years,” he said. Large predators need big, occasional dense patches of prey, and those have disappeared, he added.

Scientists have developed accurate ways to count fish. For this study, they started with a baseline from nine months of sampling in 2011 and compared it with nine subsequent surveys between 2015 and 2023. The researchers sampled deep-pelagic habitat along a large grid around the spill site from about 650 feet below the surface to about a mile down. The deep-pelagic zone accounts for about 90 percent of the Gulf’s total volume.

Across a grid of stations, scientists on slippery decks lowered and hoisted nets that open and close at different depths, with experts from different species groups to identify the catch. They sampled around noon and midnight to account for species that migrate vertically each day. Ship-mounted scientific echosounders provided an independent check, measuring sound reflected by marine life in the water column.

The research is “comprehensive and carefully composed,” marine biologist Bruce Robison, a senior scientist at the Monterey Bay Aquarium Research Institute, said via email. “There is no other study that I know of with such an incredible number of net samples,” added Robison, who did not participate in the new study.

The research focuses on species that are not commercially fished and shows for the first time that human impacts can deplete marine life even in very deep ocean water, he said.

“It is important for the public to understand just how disastrous this oil spill was,” Robison said. “The Gulf has not recovered, and it’s been over 15 years.” Robison said other activities, such as deep-sea mining, could also have severe negative consequences for deepwater pelagic ecosystems by discharging wastewater containing metals or lubricants.

Three lines of evidence—net hauls, acoustic surveys, and genetic sampling—corroborate each other, which is “unusually strong evidence to support his conclusions,” said Jeffrey Drazen, a marine ecologist at the University of Hawaii at Manoa, who did not participate in the new study.

The study examines all possible causes of the decline and shows only one aligns with the scientific evidence, he said.

“Through logical elimination,” he said, “and without actually pointing a finger, they leave no doubt that the oil spill is the cause of the decline.”