Coastal developments and sea level rise have caused a decline in tidal flats along the world coastline, according to research that has mapped the ecosystem for the first time.
Scientists from the University of New South Wales (UNSW) and the University of Queensland use machine learning to analyze more than 700,000 satellite images to map the levels and changes of tidal flats throughout the world.
The study, published in Nature, found tidal flat ecosystems in several countries declined by 16% in the years from 1984 to 2016.
Tidal flats are mud flats, sand flats or wide rock platforms that are important coastal ecosystems. They act as buffer storms and sea level rise and provide habitat for many species, including migratory birds and fish nurseries.
Nearly 50% of the global area of tides is concentrated in only eight countries: Indonesia, China, Australia, US, Canada, India, Brazil and Myanmar.
Nicholas Murray, lead author of the study and a senior researcher at the ecosystem science center at the University of New South Wales, said that because tidal flats are often at least partially covered in water, they are difficult to monitor in the past.
"This is a big ecosystem," he said. "It exists throughout the planet and is very vulnerable to threats, but we don't know where they are, which limits the ability to monitor them."
The research team worked with Google and used computational resources to analyze every satellite image ever collected from the world coastline.
They found that tidal plains, as an ecosystem, are as global as mangroves and that coastal developments and sea level rise, in particular, are causing them to decline.
In parts of China and Western Europe, they found tidal flats that reached 18 km in height. In Australia, they occur throughout the country, including places like Moreton Bay in Queensland and along the Gulf of Carpentaria.
For 17% of the world, there is enough data available to measure the decline from 1984 to 2016.
In these locations, which are mostly in China, the US, and countries in the Middle East, they find a decline in tides of 16%.
For 61% more in the world, there is enough data to analyze changes from 1999 to 2016 and research shows a 3.1% decline in this period.
Murray says airports, aquaculture and other infrastructure that have been built on tidal flats in countries like China are the main threat. Reducing the flow of sediment from rivers throughout the world also causes a reduction in the amount of sediment deposited as tidal plains.
Murray said the dam was one of the main drivers of reduced sediment flow from rivers. He said further analysis would be needed of the continuing impact of another major threat – sea level rise.
"This study has really provided data to start making these links," he said. "This means you can really begin to understand the impact of sea level rise and coastal development."
The researchers suggest this study could be used to advance protected areas for tidal plains, which are not always historically well protected because they fall between land and sea.
Maps are publicly available and Murray said he had laid the foundations for an ongoing monitoring system.
"The easiest way to think about this is, for decades we have been able to observe deforestation," he said. "We can now do that for tidal flat ecosystems.
"We can identify places where tidal flat ecosystems are being lost and the main driver of that loss, which will enable us to respond with conservation actions."