Model Suggests Dugong Grazing Could Boost Seagrass Carbon Storage

A modeling study published in Frontiers in Marine Science suggests that dugong grazing could increase seagrass carbon capture by 2.4 times and sediment carbon storage by 2.63 times in Bahrain's Halodule seagrass beds. Researchers Oswald Schmitz of Yale University and Reem AlMealla of Nuwat for Environmental Research and Education built a mathematical model tracking carbon and nitrogen flows among sediment, seagrass, and dugongs across a 145-square-kilometer area supporting roughly 700 animals.

The model compared scenarios with and without dugongs, finding that grazing which removes up to 96% of aboveground biomass and 73% of belowground biomass can still enhance carbon storage through rapid nutrient cycling. Dugong waste returns nutrients to the system faster than microbial decomposition, stimulating regrowth that outweighs carbon lost to grazing. The central estimate indicates an additional 79,700 metric tons of carbon captured annually and 638,000 metric tons stored in sediment.

However, the uncertainty ranges are enormous. The carbon capture boost ranges from 1.1 to 4.2 times, while sediment storage boost ranges from 1.1 to 7.6 times. Additional sediment carbon storage could be as low as 14,500 tons or as high as 1.36 million tons, a nearly hundredfold spread. These wide ranges exist because critical parameters were never directly measured in dugongs; researchers borrowed assumptions from studies of terrestrial grazers, sea urchins, sea turtles, and burrowing shrimp.

The authors explicitly state that the magnitude of dugong effects on seagrass net primary production and net ecosystem carbon balance has not been measured. Baseline conditions without dugongs fell within literature-reported ranges, and a single field survey near a dugong hotspot found sediment carbon 25% higher than even the model's upper estimate, but this does not validate the broader model.

The model also reveals structural fragility: a carbon-balanced ecosystem supporting roughly 700 dugongs only emerges within a narrow band of parameter values. Modest environmental disruption, such as coastal development already altering Bahrain's shoreline, could destabilize the dynamic the model describes.

Dugongs are classified as vulnerable globally, with populations functionally extinct or severely depleted across much of their historic range. If megafauna genuinely amplify blue carbon storage as the model suggests, dugong population declines could represent an underappreciated climate cost beyond biodiversity loss. The researchers frame their work as a first approximation demonstrating why animal functional roles deserve inclusion in blue carbon strategy, not proof that the numbers are correct.