Lighthouses are centuries-old symbols of our relationship with coastal hazards. Now the roughly 700 lighthouses that span the entire U.S. coastline — some of our oldest coastal structures — serve as markers to track shoreline erosion and sea level rise.

Some islands, like Seahorse Key, are slowing running out of time.

Most current sea rise prediction models suggest that the Gulf will not creep threateningly close to the Seahorse Key lighthouse until around year 2100. But, by that time, much of the lower-elevated parts of the island it towers over will be under water.

Woven into the cultural fabric of the Cedar Key area, the lighthouse at Seahorse has persevered through everything from Civil War occupation to record-breaking hurricanes. But sea level rise isn’t sentimental. It does not spare our historic monuments.

The Seahorse Key lighthouse

The sea around the cluster of islands is rising at a rate of 1.87 millimeters per year. That doesn't seem like much, but Mark Clark, a UF wetland ecologist, said it adds up.

"It’s one of those really hard things to see," Clark said.

Clark stood near Cedar Key's Joe Raines Beach as he pointed to Seahorse Key in the distance. The beach, named for a local man who opened it to the public, is full of muddy gravel instead of the white sand you’d expect. Over the past two decades, the shoreline in front of Joe Raines Beach down to the nearby Tyree Canal has been eroding.

Cedar Key's Joe Raines Beach in fall of 2016.

Clark and colleagues are in the middle of a new project designed to halt the erosion and reverse it by restoring the beach in an engineered way. A living shoreline, as the project is called, adapts to natural processes and changes more readily than a seawall.

But the living shoreline is no long-term fix for sea rise.

“Any effort you’re doing right now is a temporary measure,” Clark said. “You’re buying time.”

Walking along the beach at Seahorse Key, fiddler and horseshoe crabs scurry where sand and water meet. Small nurse sharks curiously stalk the shore. Loggerhead sea turtles and sting rays are regularly spotted in the foggy water, as are manatees making their way south to Crystal River for the winter. Raccoons, rats and reptiles inhabit the island. And an invasive trees frog lives there, with its ingenious way of reproducing on a freshwaterless island: it skips the tadpole stage, developing completely inside eggs laid in rainwater collected on leaves.