Many of the estuaries in the United States were once much larger than previously known, a critical finding as policymakers work to protect and restore these ecosystems. … The finding on current and historical estuary size comes from a study, published in November in the journal Biological Conservation, exploring how 30 of the country’s estuaries have changed from as early as 1842 to today. The study determined that estuaries along the Pacific Coast have lost, on average, more than 60% of their tidal marshes since mapping began, while tidal marshes along the East Coast have decreased in size by 8% over that span. Conversely, some Gulf of Mexico estuaries have remained stable or grown over time—migrating landward into adjacent forests—while others in that region have barely shrunk at all.