Species → Leatherback Sea Turtle
Leatherback Sea Turtle
Dermochelys coriacea
What if it disappeared?
Impact LowAn adult leatherback consumes an average of 330 kg of jellyfish per day, up to 840 kg on some days — averaging 73% of its own body weight daily — and returns year after year to specific areas where jellyfish aggregate across dozens of square kilometers.
DocumentedDetail
Heaslip, S.G., Iverson, S.J., Bowen, W.D. et James, M.C. (2012). Jellyfish Support High Energy Intake of Leatherback Sea Turtles (Dermochelys coriacea): Video Evidence from Animal-Borne Cameras. PLoS ONE, 7(3), e33259.
Measured using animal-borne cameras, which directly filmed feeding events. A complementary study (Houghton et al. 2006, Ecology) tracked jellyfish (Rhizostoma octopus) aggregation zones by aerial survey that stayed consistent year after year in the Celtic Sea, which turtles return to exploit as reliable feeding hotspots.
The idea that declining leatherback turtles (and other jellyfish predators) trigger jellyfish blooms is widely repeated in popular science writing — but a systematic review of the studies underpinning it judged the evidence largely indirect, with most of the cited articles merely showing that jellyfish have predators, without demonstrating that a decline in those predators actually increases jellyfish.
InsufficientDetail
Pitt, K.A., Lucas, C.H., Condon, R.H., Duarte, C.M. et Stewart-Koster, B. (2018). Claims That Anthropogenic Stressors Facilitate Jellyfish Blooms Have Been Amplified Beyond the Available Evidence: A Systematic Review. Frontiers in Marine Science, 5, 451.
Of the 11 articles specifically supporting the "overfishing of jellyfish predators → jellyfish bloom" mechanism, 9 rely on inference rather than a direct demonstration of the cause-and-effect link. The authors also note that jellyfish populations follow natural cycles spanning decades, which can produce misleading correlations with environmental variables absent any real causal link. This is a rare case in this reference where the claim most widely repeated by the public is precisely the one least solidly demonstrated.
The decline already under way in the Pacific (up to a 99% drop projected by 2040) could, in principle, provide a real-world test of the link between leatherback disappearance and jellyfish proliferation — but that still requires systematic monitoring of the jellyfish population in the same waters to yield an answer rather than yet another circumstantial correlation.
ExtrapolatedDetail
Extrapolation à partir des données de déclin de l'UICN sur la population du Pacifique et de la mise en garde méthodologique de Pitt et al. (2018), sans qu'un tel suivi comparatif n'ait encore été mené.
The Pacific decline is one of the best-documented and fastest for any large marine predator in this reference. It represents a real opportunity to rigorously test the jellyfish-turtle hypothesis, provided independent monitoring of jellyfish populations in the same waters accompanies the turtle monitoring already under way.
What's missing to confirm it: Direct comparative monitoring of Pacific jellyfish populations, conducted alongside leatherback turtle monitoring, would make it possible to test the hypothesis rather than rely on inference.
Documentation
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IUCN Red List — Dermochelys coriacea, statut mondial et régional (Pacifique / Atlantique Nord-Ouest)
Accessed August 7, 2026
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Heaslip, Iverson, Bowen & James (2012) — Jellyfish Support High Energy Intake of Leatherback Sea Turtles, PLoS ONE
Accessed August 7, 2026
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Houghton, Doyle, Wilson, Davenport & Hays (2006) — Jellyfish aggregations and leatherback turtle foraging patterns, Ecology
Accessed August 7, 2026
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Pitt, Lucas, Condon, Duarte & Stewart-Koster (2018) — Claims That Anthropogenic Stressors Facilitate Jellyfish Blooms Have Been Amplified Beyond the Available Evidence, Frontiers in Marine Science
Accessed August 7, 2026
Last verified: August 7, 2026