Dugongs and blue carbon connect in a new modeling study, suggesting that the grazing marine mammals could enhance seagrass carbon capture by 2.4 times and sediment carbon storage by 2.63 times.
Dugongs and blue carbon research published in Frontiers in Marine Science addresses a genuine gap in climate accounting. Seagrass meadows cover less than 0.2% of the ocean but store carbon disproportionate to their footprint, making them increasingly central to countries’ climate pledges under the Paris Agreement. Yet most seagrass carbon budgets assume the ecosystem is controlled purely from the bottom up, by sediment nutrients and plant growth, largely ignoring what grazing animals do to that equation.
Dugongs or sea cows feed almost exclusively on seagrass and can have a dramatic impact, stripping up to 96% of aboveground biomass and 73% of belowground biomass from grazed patches. That destructive capacity is precisely why earlier assumptions treated dugongs as a carbon liability rather than an asset. Researchers Oswald Schmitz of Yale University and Reem AlMealla of Nuwat for Environmental Research and Education in Bahrain built a mathematical model to test whether that assumption holds.
The study focused on Bahrain’s Halodule seagrass beds, a 145-square-kilometer area supporting one of the largest known dugong populations outside Australia, with an aggregate herd size of around 700 animals and a total population estimated between 530 and 1,798. The model tracked carbon and nitrogen flows among sediment, seagrass, and dugongs, comparing scenarios with and without dugongs.
Bahrain’s Halodule seagrass beds support one of the largest known dugong populations outside Australia, with herds of roughly 700 animals. Photo by Benjamin L. Jones on Unsplash.
Grazing that removes nearly all standing biomass can still help store more carbon, according to the model, through a mechanism rooted in nutrient cycling rather than biomass preservation. Dugong waste, urine, feces, and carcass matter release nutrients rapidly back into the system, bypassing the slower process of microbial decomposition. That fast recycling appears to stimulate seagrass regrowth vigorously enough to outweigh the carbon lost through grazing itself.
The magnitude of the modeled effect is substantial. Across the full 145-square-kilometer of the dugongs and blue carbon study area, dugong presence corresponds to an estimated additional 79,700 metric tons of carbon captured annually and 638,000 metric tons stored in sediment. Researchers note this is comparable in scale to 10 to 30 percent of Bahrain’s annual emissions from sectors like transport, oil and gas production, and aviation, a striking comparison if the numbers hold up.
They may not hold up precisely. The uncertainty ranges attached to these figures are enormous. The estimated boost to carbon capture ranges from 1.1 to 4.2 times, and the boost to sediment storage ranges from 1.1 to 7.6 times, meaning the true effect could be marginal or dramatically larger than the central estimate suggests. The metric-ton ranges are even starker: additional sediment carbon storage could be as low as 14,500 tons or as high as 1.36 million tons, a nearly hundredfold spread.
That uncertainty exists because critical parameters were never directly measured in dugongs. The dugongs and blue carbon researchers had to borrow assumptions from studies of terrestrial grazers, sea urchins, sea turtles, and burrowing shrimp to estimate how dugong foraging affects nutrient uptake and sediment disturbance. The authors are explicit about this limitation: “the magnitude of dugong effects on seagrass NPP and NECB has not been measured,” meaning the model’s central predictions cannot yet be checked against direct field data on dugongs themselves.
What the researchers compared against real measurements were baseline conditions without dugongs, which fell within literature-reported ranges, and a field survey near a known dugong hotspot that found sediment carbon 25% higher than even the upper end of the model’s dugong-present estimate. That’s suggestive, but a single targeted comparison in one small area doesn’t validate the broader model, and the authors explicitly call for controlled field research that directly quantifies dugong effects on carbon cycling.
There’s also a structural fragility buried in the modeling: the researchers found that a carbon-balanced ecosystem supporting roughly 700 dugongs only emerges within a narrow band of parameter values, meaning that modest environmental disruption, such as the coastal development already altering Bahrain’s shoreline, could destabilize the very dynamic the model describes.
The implications extend beyond Bahrain if the findings hold. Dugongs are classified as vulnerable globally, with populations functionally extinct or severely depleted across much of their historic range in Southeast Asia and East Africa. If megafauna genuinely amplify blue carbon storage as this model suggests, then dugong population declines represent an underappreciated climate cost, not merely a biodiversity one, and the conservation of grazing marine mammals could belong in national carbon accounting alongside mangrove and seagrass protection itself.
Dugongs and blue carbon remain, for now, a promising hypothesis built on a mathematically sound but empirically thin foundation. The researchers frame their own work accurately: a first approximation demonstrating why animal functional roles deserve inclusion in blue carbon strategy, not proof that the numbers are right.
