What If Gone

Species → Dugong

Dugong

Dugong dugon

No reliable global figure — the species is too dispersed across its…
Extinction risk Vulnerable
Ecosystem engineerMarine environmentMarine herbivoreMegaherbivoreCarbon
Dugong (Dugong dugon)
Photo: Julien Willem, Wikimedia Commons (CC BY-SA 3.0)

What if it disappeared?

Impact Moderate
1 year

Without a dugong grazing a seagrass meadow hard, it no longer gets the push that makes it regrow richer in nitrogen: within the first year, the gap can reach 35% less than a meadow that stayed under active grazing.

Documented
Detail

Aragones, L.V., Lawler, I.R., Foley, W.J. et Marsh, H. (2006). Dugong grazing and turtle cropping: grazing optimization in tropical seagrass systems? Oecologia, 149(4), 635–647.

By experimentally simulating light and intensive grazing on two tropical Queensland seagrass meadows, then measuring regrowth after 11 to 13 months, the authors show that the dugong's preferred species (Halophila ovalis and Halodule uninervis) that stay intensively grazed regrow with nitrogen concentrations 35% and 25% higher, respectively, than areas left ungrazed — the state a meadow would return to within the first year without dugongs. A gain tempered by lower starch and higher fiber content, and one that green turtle grazing partly reproduces (+30% nitrogen on Halophila ovalis).

10 years

That loss carries over into stored carbon: according to a model of a comparable meadow in Bahrain, a site left without dugongs for years would capture roughly two and a half times less carbon in its sediment than a meadow still grazed by a population of about 700 individuals.

Extrapolated
Detail

Extrapolation à partir de Schmitz, O.J. et AlMealla, R.K. (2026). Integrating megafauna into blue carbon strategies: dugongs could enhance seagrass carbon storage. Frontiers in Marine Science, 13, 1816090 — un modèle, pas une mesure de terrain du stock de carbone avant et après broutage.

The model estimates that roughly 700 dugongs on a 145 km² meadow in Bahrain would multiply the ecosystem's net primary production and net carbon balance by 2.4 on average (range 1.1 to 4.2) and sediment carbon storage by 2.6 on average (range 1.1 to 7.6), representing about 79,000 additional tonnes of carbon captured each year. This is a numerical projection, not a repeated field measurement before and after an actual disappearance.

What's missing to confirm it: No direct field measurement, before and after an actual disappearance of dugongs on a comparable meadow, yet confirms the pace at which this gap in carbon storage would widen over a decade.

100 years

Along Queensland's urban coast, the dugong population fell from about 72,000 individuals in the early 1960s to about 4,220 in the mid-1990s, down to just 3.1% of its original level. If this near-disappearance held for a century, the seagrass meadows they once grazed would plausibly have lost, on a wide scale, the regrowth vigor and nitrogen richness that grazing sustained elsewhere.

Hypothesis
1000 years

Over a thousand years, even if dugongs returned in force, the meadow likely would not simply spring back to its earlier form: the species that benefit least from grazing would have had plenty of time to dominate the seabed, and the carbon that failed to accumulate throughout that time would not be made up all at once.

Hypothesis

Documentation

Last verified: August 16, 2026