Scientists from the University of New South Wales (UNSW) and the University of Queensland used machine-learning to analyse more than 700,000 satellite images to map the extent of and change in tidal flats around the globe.
The study, published in Nature, found tidal flat ecosystems in some countries declined by as much as 16% in the years from 1984 to 2016.
Tidal flats are mud flats, sand flats or wide rocky reef platforms that are important coastal ecosystems. They act as buffers to storms and sea level rise and provide habitat for many species, including migratory birds and fish nurseries.
Almost 50% of the global extent of tidal flats is concentrated in just eight countries: Indonesia, China, Australia, the US, Canada, India, Brazil and Myanmar.