Some marine life in the deep Gulf hasn't bounced back from the 2010 Deepwater Horizon oil spill, according to one of the longest analyses of deep-water animals to date.
And there's no clear timeline for recovery.
Between 4 million and 4.9 million barrels of oil were released into the depths of the Gulf, followed by 770,000 gallons of chemical dispersant to break up oil slicks into droplets.
A group of nearly 50 scientists across 11 institutions banded together over the years to form the DEEPEND Consortium, studying the impacts on the marine animals that swim from the surface down to 1,500 meters.
They’ve gone on two- to three-week long research cruises 12 times, in which they deployed a netting system that drops six nets at different levels of the water column at the same time to collect the animals they study.
“We recognize it's a very rare habitat, and it's not an easy ecosystem to study. So, because of all of this, we are extremely cognizant of collecting and saving every single organism we get,” said Heather Judkins, an invertebrate zoologist with the University of South Florida.
“We have all of them preserved in various locations at our institutions for future studies. Some of these need to have guts removed. Some of them need to have tissue samples dealt with.”
Between 2011 and 2023, they found oil-related compounds still lingering in deep-water fish eggs and in the tissue of cephalopods, like squid.
Contamination like this can cause death or developmental damage that can prevent mating in some cases.
Overall, the researchers documented a decline of 64% in fishes, 62% in large crustaceans and 60% in small squid and other cephalopods. Plus, krill declined by nearly 73%, lanternfishes by 63%, and bristlemouth fishes by 69%.
"The declines that we saw in terms of abundance, some of the declines we saw in terms of genetic diversity and in terms of acoustics was quite alarming and surprising over a short time period,” said Heather Bracken-Grissom, a marine evolutionary biologist at Florida International University.
They paired the net samplings with acoustic surveys, led by Kevin Boswell at FIU.
“We saw the same thing acoustically, where we saw backscatters decline significantly … All summed up together, this was a pretty large-scale event that occurred, and I think probably surprised us all,” said Boswell.
In 2011, dense patches of these prey animals were common but then they pretty much disappeared – and they’re essential for feeding whales, dolphins, tuna, sharks, seabirds, and other predators.
"Think about our tuna and our other big commercial fishes, the marine mammals, of course, birds ... So, there could be changes in their feeding and behavior patterns due to the less abundance of their prey,” said Judkins.
Although they observed declines across all three major groups of fishes, crustaceans, and cephalopods, there was some genetic diversity observed depending on the species.
“Not everything is going to be affected similarly. And depending on reproduction and how long they live and different strategies, they probably, at the individual species level, are responding a little bit differently,” said Bracken-Grissom.
The consortium's findings were recently peer-reviewed and published in the scientific journal PNAS, entitled Immense but not immutable: A sudden and sustained decline in deep-pelagic life in a large oceanic ecosystem.
The scientists, led by led by Tracey T. Sutton from Nova Southeastern University, are going on their next research cruise in June of 2027, but they're looking for future funding to keep the documentation going.
