You’ve heard of rainforests. You’ve heard of coral reefs. But there’s a third ecosystem quietly doing heavy lifting for the planet, one most Australians have never even seen.
Seagrasses are flowering plants that grow entirely underwater in shallow coastal bays and estuaries. They look unremarkable, like tufts of grass on the seafloor, but they are among the most productive ecosystems on Earth. Australia holds roughly 10 percent of the world’s seagrass species, 160,000 square kilometres exist globally, and these plants have been photosynthesising on the seafloor for 100 million years.
The map tells a striking story. Hover over any country to see its seagrass carbon stock, and watch the bubbles for how much seagrass extent has been lost over time.
Australia, outlined in red on the map, stores an estimated 13.2 teragrams of carbon in its seagrass meadows. That’s more than twice its nearest rival, Indonesia, and roughly a third of the entire global total.
Yet seagrass receives a fraction of the conservation funding directed at coral reefs, despite storing carbon for centuries rather than decades.
Researchers expected decline across most bioregions, but the scale of loss in Australia’s two bioregions has exceeded those expectations.
Hover over the bars on the right to see the actual net change in seagrass extent for each bioregion since 1880. Australia sits across the Temperate Southern Oceans, down 22.4 percent, and the Tropical Indo Pacific, down 16.2 percent, both marked with a star.
The drivers behind these declines are well documented: agricultural runoff, coastal development, and increasingly frequent marine heatwaves. Unlike forests, seagrass meadows can take decades to recover after a major disturbance.
Here’s what most climate reporting misses. When seagrass dies, it doesn’t just stop absorbing carbon, it releases centuries of buried carbon back into the atmosphere.
Most of that carbon isn’t in the seagrass leaves themselves. It’s locked in the sediment beneath the meadow, built up over millennia. When the plants disappear, the sediment carbon is what gets released.
At stake is the equivalent of more than a year of emissions from every car in Australia, sitting in shallow coastal waters, largely unprotected.
Australia is the world’s single largest seagrass carbon reserve. At 13.2 teragrams of carbon, Australia’s seagrass meadows store more than twice as much carbon as the next highest country, Indonesia, and account for roughly a third of the global total identified by Gomis et al. (2025). This single fact reframes seagrass conservation from a niche ecological concern into a matter of national climate significance.
Decline has been worse than researchers expected, even though decline was expected. Across the seven seagrass bioregions studied by Dunic et al. (2021), most researchers anticipated some level of decline. However, when comparing those expectations against the actual net change in seagrass extent (Gomis et al. 2025), Australia’s two bioregions, the Temperate Southern Oceans and the Tropical Indo Pacific, show losses of 22.4 percent and 16.2 percent respectively. The gap between expectation and reality suggests that existing monitoring and modelling may be underestimating the pace of seagrass loss, with implications for how confidently we can rely on current projections.
Most of the carbon at risk is invisible, because it is underground. A common assumption is that the carbon value of an ecosystem lies mainly in its visible biomass, the leaves and stems. The data tells a different story: sediment carbon accumulated over millennia represents the overwhelming majority of what is at risk, dwarfing the carbon held in plant biomass itself. This has a direct policy implication: protecting seagrass is not just about protecting plants, it is about protecting the seafloor sediment beneath them, which means activities like dredging and bottom trawling pose a disproportionate risk relative to their visible footprint.
The carbon at stake is comparable to a major national emissions source. The carbon currently at risk in Australia’s seagrass meadows is broadly equivalent to more than a year of emissions from the entire Australian car fleet. Framed this way, seagrass protection is not a marginal environmental issue but a climate mitigation opportunity on a scale comparable to major transport policy interventions, at potentially a fraction of the cost.
There is a clear and underused policy lever. Unlike many climate solutions that require new technology, seagrass protection mostly requires reducing existing pressures, agricultural runoff, coastal development, and dredging, that are already regulated to varying degrees. Combined with emerging blue carbon credit frameworks, this suggests Australia has a comparatively low cost, high impact climate action available that remains largely outside public discussion.
Seagrass restoration projects are underway in Western Australia, Queensland, and South Australia. Blue carbon credits, which allow seagrass restoration to be traded as a climate solution, are gaining traction in Australian policy.
Reducing agricultural runoff and coastal development pressures costs a fraction of what seagrass is worth as a carbon asset.
The story isn’t without hope. Seagrass, unlike many ecosystems, can recover if we reduce the pressures driving its loss.
Several restoration projects are already underway across Australia’s coastline, and blue carbon policy frameworks are beginning to recognise seagrass alongside mangroves and saltmarshes.
But protection requires awareness, and right now, almost none exists. That’s the story Australia needs to tell.
Dunic, J. C., Brown, C. J., Connolly, R. M., Turschwell, M. P., & Côté, I. M. (2021). Long‐term declines and recovery of meadow area across the world’s seagrass bioregions. Global Change Biology, 27(17). https://doi.org/10.1111/gcb.15684
Gomis, E., Strydom, S., Foster, N. R., Montemayor, D., Mateo, M. A., Serrano, E., Inostroza, K., McCallum, R., Lafratta, A., Webster, C. L., O’Dea, C. M., Said, N. E., Dunham, N., Bernasconi, R., Werner, A., Vitelli, F., Viena Puigcorbé, D’Cruz, A., Salinas, C., & McMahon, K. M. (2025). Global estimates of seagrass blue carbon stocks in biomass and net primary production. Nature Communications, 16(1), 9530–9530. https://doi.org/10.1038/s41467-025-64667-6
Salinas, C., Duarte, C. M., Lavery, P. S., Pere Masque, Arias-Ortiz, A., Leon, J., Callaghan, D., Kendrick, G. A., & Serrano, O. (2020). Seagrass losses since mid-20th century fuelled CO2 emissions from soil carbon stocks [dataset]. Research Online. https://doi.org/10.25958/5ed5bab3b80bc
Australian Bureau of Statistics. (2023). Australian Bureau of Statistics, Australian Government. Abs.gov.au. https://www.abs.gov.au