References
[1] Irigoien, X., Klevjer, T. A., Røstad, A., et al. (2014). Large mesopelagic fishes biomass and trophic efficiency in the open ocean. Nature Communications, 5, 3271. https://doi.org/10.1038/ncomms4271
[2] Martin, A., Boyd, P., Buesseler, K., et al. (2020). The oceans’ twilight zone must be studied now, before it is too late. Nature, 580, 26–28. https://doi.org/10.1038/d41586-020-00915-7
[3] Behrenfeld, M. J., Gaube, P., Della Penna, A., et al. (2019). Global satellite-observed daily vertical migrations of ocean animals. Nature, 576, 257–261. https://doi.org/10.1038/s41586-019-1796-9
[4] Pinti, J., DeVries, T., Norin, T., et al. (2023). Model estimates of metazoans' contributions to the biological carbon pump. Biogeosciences, 20(5), 997–1009. https://doi.org/10.5194/bg-20-997-2023
[5] Martin, A. H., Scheffold, M. I. E., & O'Leary, B. C. (2023). Changing the narrative and perspective surrounding marine fish. Marine Policy, 156, 105806. https://doi.org/10.1016/j.marpol.2023.105806
[6] Martin, A., Boyd, P., Buesseler, K., et al. (2020). The oceans’ twilight zone must be studied now, before it is too late. Nature, 580, 26–28. https://doi.org/10.1038/d41586-020-00915-7
[7] Martin, A. H., Scheffold, M. I. E., & O'Leary, B. C. (2023). Changing the narrative and perspective surrounding marine fish. Marine Policy, 156, 105806. https://doi.org/10.1016/j.marpol.2023.105806
[8] Schmitz, O. J. et al. 2023. Trophic rewilding can expand natural climate solutions. Nature Climate Change 13: 324–333. https://doi.org/10.1038/s41558-023-01631-6
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Mesopelagic Fish
Every night, billions of fish migrate through the ocean’s “twilight zone,” helping move carbon from the surface into the deep sea, where it can remain stored for centuries.
Between 200 and 1,000 metres below the ocean’s surface lies the mesopelagic zone - a vast and dimly lit layer often called the ocean’s “twilight zone.” Too deep for most sunlight to penetrate, this ecosystem stretches across the entire globe and is assumed to contain the largest concentrations of fish biomass on Earth.[1] Despite its scale, it remains one of the least studied parts of the ocean.[2]
Every night, billions of mesopelagic fish rise toward the surface to feed on plankton and other carbon-rich organisms. Before dawn, they descend again into deeper waters to avoid predators. Scientists describe this daily movement, known as diel vertical migration, as one of the largest animal migrations on Earth.[3] [4]
As these fish move through the water column, they also transport carbon. Carbon consumed near the surface is carried into deeper waters through respiration, waste production, and eventually the sinking of dead organisms. Because this carbon is transported to the deep, it can remain isolated from the atmosphere for centuries, making these migrations an important part of the ocean’s biological carbon pump.[4]
Recent research suggests this role may be even more significant than previously understood. A 2023 modelling study found that fish and other marine animals account for only around 20% of carbon exported from the ocean's surface, but are responsible for more than 50% of all carbon that ends up sequestered by the biological pump. Marine animals tend to transport carbon to greater depths, where it stays locked away for around 250 years on average, far longer than previously reported for other components of the biological pump.[4]
Mesopelagic fish are also a vital link in the ocean food web. As both predator and prey, they feed on plankton, shrimp, and other small organisms, while also serving as a major food source for larger animals including tuna, whales, squid, dolphins, sharks, and seabirds.[5] Their decline could therefore affect not only carbon storage, but also the wider structure and stability of marine ecosystems.
Until recently, the mesopelagic zone has remained only lightly exploited by commercial fishing. However, growing interest in using mesopelagic fish for fishmeal and fish oil in aquaculture and livestock feed is increasing pressure on this ecosystem. Scientists warn that large-scale extraction could weaken natural carbon-storage processes in the open ocean while disrupting marine food webs that depend on these fish.[6] [7]
Indeed, global marine fish contribute an estimated 5.5 gigatonnes of carbon each year through their movement and interactions within marine food chains, with mesopelagic fish playing a particularly important role in marine fish carbon flux.[8]
Mesopelagic Fish
Every night, billions of fish migrate through the ocean’s “twilight zone,” helping move carbon from the surface into the deep sea, where it can remain stored for centuries.
Between 200 and 1,000 metres below the ocean’s surface lies the mesopelagic zone - a vast and dimly lit layer often called the ocean’s “twilight zone.” Too deep for most sunlight to penetrate, this ecosystem stretches across the entire globe and is assumed to contain the largest concentrations of fish biomass on Earth.[1] Despite its scale, it remains one of the least studied parts of the ocean.[2]
Every night, billions of mesopelagic fish rise toward the surface to feed on plankton and other carbon-rich organisms. Before dawn, they descend again into deeper waters to avoid predators. Scientists describe this daily movement, known as diel vertical migration, as one of the largest animal migrations on Earth.[3] [4]
As these fish move through the water column, they also transport carbon. Carbon consumed near the surface is carried into deeper waters through respiration, waste production, and eventually the sinking of dead organisms. Because this carbon is transported to the deep, it can remain isolated from the atmosphere for centuries, making these migrations an important part of the ocean’s biological carbon pump.[4]
Recent research suggests this role may be even more significant than previously understood. A 2023 modelling study found that fish and other marine animals account for only around 20% of carbon exported from the ocean's surface, but are responsible for more than 50% of all carbon that ends up sequestered by the biological pump. Marine animals tend to transport carbon to greater depths, where it stays locked away for around 250 years on average, far longer than previously reported for other components of the biological pump.[4]
Mesopelagic fish are also a vital link in the ocean food web. As both predator and prey, they feed on plankton, shrimp, and other small organisms, while also serving as a major food source for larger animals including tuna, whales, squid, dolphins, sharks, and seabirds.[5] Their decline could therefore affect not only carbon storage, but also the wider structure and stability of marine ecosystems.
Until recently, the mesopelagic zone has remained only lightly exploited by commercial fishing. However, growing interest in using mesopelagic fish for fishmeal and fish oil in aquaculture and livestock feed is increasing pressure on this ecosystem. Scientists warn that large-scale extraction could weaken natural carbon-storage processes in the open ocean while disrupting marine food webs that depend on these fish.[6] [7]
Indeed, global marine fish contribute an estimated 5.5 gigatonnes of carbon each year through their movement and interactions within marine food chains, with mesopelagic fish playing a particularly important role in marine fish carbon flux.[8]