A global map of tidal flats - sand, rock, or mud flats that undergo regular tidal inundation - and changes to these coastal ecosystems is published online in Nature this week. The findings reveal that in regions with sufficient data (17.1% of the mapped area), 16% of tidal flats have been lost in the period from 1984 to 2016.
Tidal flat ecosystems provide important services such as storm protection, shoreline stabilization, and food production, which support the livelihoods of millions of people worldwide. However, they are under intense pressure from various factors, including coastal development, sea-level rise, and erosion. Despite being among the most widespread coastal ecosystems, the global distribution and status of tidal flats remain unknown, hindering efforts to manage and protect them.
Nicholas Murray and colleagues used around 700,000 satellite images to map the global extent and change in tidal flats from 1984 to 2016. The authors found that at least 127,921 km2 of the Earth’s surface are tidal flat ecosystems, an area similar to that occupied globally by mangroves. About 50% of tidal flats occur in just eight countries, located across three continents: Asia, North America, and South America. By country, Indonesia has the greatest extent of tidal flats, followed by China and Australia. In regions where the authors had sufficient satellite data over the 33-year timeframe, they found that tidal flats have declined by about 16%. This suggests a potential global loss of more than 20,000 km2 of tidal flats since 1984.