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
Over one year, Queensland

By grazing a seagrass meadow intensively, the dugong stimulates regrowth of seagrass that is richer in nitrogen — up to 35% more than an ungrazed meadow after a year — rather than simply depleting the resource it feeds on.

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 1 to 4 months and after 11 to 13 months, the authors show that the dugong's preferred species (Halophila ovalis and Halodule uninervis) regrow with nitrogen concentrations 35% and 25% higher, respectively, than ungrazed controls after a year — a gain nonetheless tempered by lower starch and higher fiber content. Green turtle grazing produces a comparable effect (+30% nitrogen on Halophila ovalis).

Over 37 years, Queensland

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 — a decline of 8.7% a year, down to just 3.1% of its original level.

Documented
Detail

Marsh, H., De'ath, G., Gribble, N. et Lane, B. (2005). Historical marine population estimates: Triggers or targets for conservation? The dugong case study. Ecological Applications, 15(2), 481–492.

The authors reconstruct the scale of the decline by combining 1990s aerial surveys with the bycatch rate of dugongs in shark control nets installed along six coastal sites between 16.5°S and 28°S — an indirect method, but the only continuous series available since the 1960s, before systematic aerial surveys began.

By modeling, Bahrain

A model applied to a 145 km² seagrass meadow in Bahrain estimates that a population of about 700 dugongs would multiply sediment carbon storage there by 2.6 on average — but this is a numerical projection, not yet a direct field measurement.

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 dugong presence 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 roughly 79,000 additional tonnes of carbon captured each year across the study area. The wide ranges reflect the uncertainty of a modeling exercise rather than a repeated field measurement.

What's missing to confirm it: No direct field measurement, before/after an actual change in dugong density, yet confirms the magnitude of this carbon-storage effect predicted by the model.

Documentation

Last verified: August 14, 2026