According to studies that first discovered ecosystems, the development of coastal zones and rising sea levels cause a decrease in tidal plains along the coastline of the world.
Scientists from the University of New South Wales (UNSW) and the University of Queensland used machine learning to analyze more than 700,000 satellite images to map the extent and changes of tidal plains around the globe.
A study published in the journal Nature found that tidal ecosystems in some countries declined by as much as 16% between 1984 and 2016.
Tidal plains are mud, sandy or wide rocky reef platforms that are important coastal ecosystems. They act as a buffer for storms and rising sea levels and provide habitat for many species, including migratory birds and fish farms.
Almost 50% of the global area of tidal flats is concentrated in just eight countries: Indonesia, China, Australia, USA, Canada, India, Brazil and Myanmar.
Nicholas Murray, lead author and senior researcher at the Center for the Study of Ecosystems at the University of New South Wales, said that tidal plains were often at least partially covered by water that was difficult to control in the past.
“This is a large ecosystem,” he said. “It's all over the planet and very susceptible to threats, but we don’t know where they are, which limits their monitoring capabilities.”
The research team worked with Google and used its computing resources to analyze all the satellite images ever collected on the coastlines of the world.
They found that tidal plains, like an ecosystem, were as extensive around the world as mangrove forests, and that the development of coastal zones and rising sea levels, in particular, caused their decline.
In some areas of China and Western Europe, they found tidal plains up to 18 km wide. In Australia, they are found throughout the country, including in places such as the Moreton Bay in Queensland and along the Gulf of Carpentaria.
For 17% of the world, there was enough data to measure the decline from 1984 to 2016.
In these places, which were mainly in China, the United States and the countries of the Middle East, they found a 16% decrease in tidal ebb.
For another 61% of the countries in the world, there was enough data to analyze changes from 1999 to 2016, and the study showed a decrease of 3.1% during this period.
Murray said that the main threats were airports, aquaculture and other infrastructure, which was built on top of tidal flats in countries such as China. Reducing sediment flows from rivers around the world has also led to a decrease in the amount of sediment in the form of tidal ebb.
Murray said dams were a major factor in reducing sediment discharge from rivers. He said that further analysis would be needed of the continuing impact of another key threat, rising sea levels.
“This study did provide data for creating these links,” he said. "This means that you can really begin to understand the impact of rising sea levels and coastal development."
The researchers suggest that the study could be used to promote protected areas for tidal flats, which have not always been so well protected historically because they are between land and sea.
The map is publicly available, and Murray said that it laid the foundations for a permanent monitoring system.
“The easiest way to think about it is for decades we have seen deforestation,” he said. “Now we can do this for tidal ecosystems.
"We can identify places where tidal flat ecosystems are lost, and the main driving forces of these losses, which will allow us to take conservation measures."