NEW PAPER: Immense but not immutable: A sudden and sustained decline in deep-pelagic life in a large oceanic ecosystem
It's been a long time in the works, but I am so excited to be able to share our new research paper, "Immense but not immutable: A sudden and sustained decline in deep-pelagic life in a large oceanic ecosystem", which was published as an open-access research paper this week in PNAS.
This work is the culmination of 16 years of work from the DEEPEND research consortium highlights evidence for a major decrease in the abundances of deep-living pelagic micronekton (small fishes, crustaceans, and cephalopods between roughly 2 and 20 cm in length) in the years following the Deepwater Horizon oil spill in the Gulf of Mexico back in 2011. In the paper, we use an unprecedented time-series of data spanning 2011 to 2023 to show that numbers of these animals declined by roughly two-thirds between 2011 and 2015 and still show no sign of recovery to date. Data from net catches are reinforced by complementary active acoustic data and genomic data that show similar trends in the midwater fauna, indicating that real and substantive change has occurred in the deep-pelagic Gulf, with real consequences for predatory species (e.g., fishes and marine mammals) that prey upon them. Indeed, similar long-term work on toothed whales in the Gulf suggests that those species that feed on lanternfishes (one of the major fish groups in the deep midwater) have also experienced major declines since 2010.
Shrimp, fishes and cephalopods have all declined by around 60% in the years following the oil spill and are showing no recovery to date. Images copyright Dante Fenolio / DEEPEND.
While we can't be certain about the causes of the decline, we have spent much of the past several years ruling out various possibilities that this event was driven by changes in temperature, oxygen, or other environmental changes. None of those fit the bill, and so we are left with the oil spill and the chemical dispersants added to region in the immediate aftermath as the most likely causes of the observed decline.
Importantly, the lack of observed recovery in the ecosystem so far suggests that these ecosystems may be far more vulnerable to human impacts than we had previously thought. The deep-pelagic realm has often been considered relatively robust to change due to its vast size and the fact that the fauna are highly dispersed which should facilitate immigration from other regions and aid in recovery. High biodiversity ecosystems, like we have in the deep-pelagic Gulf, are also thought to be generally more robust against impacts. The fact that we are seeing such a persistent decline not only highlights the potential vulnerabilities of these vast areas of the deep oceans, but highlights how much we still have to learn about them.
If you have questions about the paper, please feel free to reach out.
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