Our planet’s coastlines – where land and ocean meet in a constant conversation, shaped by tides, winds, and time.

Though they account for just a narrow slice of Earth’s surface, coastal ecosystems play an outsized role in the planet’s health.

They store carbon.

They buffer storms.

They shelter marine life and support millions of people worldwide.

And yet, they are among the most threatened environments on Earth.

To protect them, we need to understand them.

And to understand them, we need to see how they change over time.

That’s where Landsat comes in.

Since 1972, the Landsat program—a joint partnership between NASA and the U.S. Geological Survey—have used satellites to orbit the Earth, monitoring the constantly evolving surface of our planet.

With an archive spanning over half a century, Landsat lets scientists watch coastlines evolve across decades, revealing trends that might otherwise be invisible.

Like what happened to mangroves along the coasts of Florida.

The Sunshine State is home to the vast majority of mangroves in the United States.

These salt-tolerant forests protect shorelines from erosion, serve as fish nurseries, and sequester large amounts of carbon.

But they’re also vulnerable—especially to hurricanes, an unfortunately frequent seasonal occurrence in Florida

Using decades of Landsat data, researchers developed a new tool called DECODER for tracking mangrove conditions over time.

Short for DEtection and Characterization Of tiDal wEtland change and Recovery, DECODER analyzed how vegetation signals change after disturbances, allowing researchers to identify whether a mangrove forest is recovering, declining, or holding steady, information vital for understanding resilience.

In some areas, mangroves bounce back quickly after storms.

In others, they enter long-term decline—or never recover at all.

With the help of Landsat, researchers can map these unseen patterns across the entire state, year after year, helping to guide restoration efforts where they’re needed most.

While Florida’s mangroves struggle to adapt to a rapidly changing world, far to the north in Eastern Canada, a very different story is playing out.

Beneath the waters of the Gulf of St. Lawrence, you’ll find sprawling underwater meadows of eelgrass – a foundational seagrass species in coastal ecosystems.

Seagrasses like eelgrass stabilize sediment, absorb carbon, and offer shelter for fish and invertebrates.

But around the world, these meadows are shrinking—threatened by warming seas, murky waters, and coastal development.

So, when researchers from the Université du Québec decided to track decades of eelgrass growth in the waters of the Gulf of St. Lawrence, they were pleasantly surprised to find they were actually expanding.

By analyzing 40 years of Landsat imagery—specifically those taken at low tide, when eelgrass beds become visible—researchers tracked the growth of meadows in four key regions.

And they found a remarkable pattern – in each subregion, eelgrass coverage increased significantly.

In every region, eelgrass coverage expanded—some meadows growing ten, even twenty times larger than they were in the 1980s.

In the Bay of Sept-Îles, eelgrass now blankets over 80% of the intertidal zone.

Exactly what is behind this resurgence is still being investigated – it may be linked to warming temperatures, reduced sea ice, or changes in sediment and currents.

But one thing is clear: without Landsat, this story might have gone entirely unnoticed.

While it may sound intimidating, you don’t need to be scientist to track the health of Earth’s coastal ecosystems with Landsat.

And for those looking to explore coastal changes themselves from the comfort of their own homes, there’s a new tool.

NASA’s STREAM tool—short for Satellite Time-Series and Region Analysis for Marine Environments—puts Landsat water quality data right at your fingertips.

From water transparency to suspended sediment and chlorophyll levels, STREAM helps users visualize how the coastal zone is changing across space and time.

It’s just one more way Landsat is helping us understand what’s happening at the edge of land and sea.

Because whether it’s a thriving meadow of eelgrass along the coast of Quebec or a struggling mangrove forest in Florida, the health of coastal ecosystems tells us something deeper about the planet itself.

With Landsat, we can track these subtle signs of change—growth where we thought there was loss, and vulnerability where we hoped for resilience.

And in a world where the pace of change is accelerating, that long-term perspective matters more than ever.

The tide is always moving. And Landsat gives us a way to follow it.