Shifting Sands A pre-Civil War lighthouse and its species-rich island face sea level rise

The unnamed hurricane hit at dawn without warning. Its tidal wave and winds swept away an entire town on Florida's Atsena Otie Key in 1896, leaving people clinging to red cedars.

Legend has it the lighthouse a few miles northwest, sitting atop an ancient sand dune that stretches across a seahorse-shaped island like its backbone, stayed lit throughout the storm. Today, Atsena Otie Key and the lighthouse at Seahorse Key are part of thirteen barrier islands making up the Cedar Keys National Wildlife Refuge in Florida’s Big Bend region, the largest estuary in the U.S, even larger than Chesapeake Bay.

More than a century after the 1896 hurricane, there is still no record of the lighthouse at Seahorse Key — the outermost island of the refuge and home to the University of Florida's Seahorse Key Marine Lab — ever sustaining major damage from a natural disaster. During Hurricane Hermine in September of 2016, the building lost a single screened window. Nearby, kayaks floated through the streets of Cedar Key unmanned as storm surge inundated the town.

At nearly 50 feet above sea level, the lighthouse is built at the highest elevation on Florida’s west coast. The mortar between its whitewashed bricks has baked in the sun for 162 years, though every one appears to be in place as the day it was built. Its painted hardwood floors have been repainted numerous times. Peeling reveals conflicting shades of green. But the floors do not creak.

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.

"Seahorse Key has been a really important site for a long time," said Peter Frederick, a UF wetlands ecologist. “It’s been a major, long-term, multi-species rookery."

There are indicators, however, that the birds’ primary prey, fish, is changing. Mike Allen, director of the Nature Coast Biological Station, said climate change has caused fish normally found further south, like the common snook and some tropical parrotfish, to show up in area waters.

But Allen said the most immediate threat to the region isn’t climate change or sea rise, it’s groundwater pumping. The drawing down of the Floridan Aquifer has resulted in saltwater intrusion. In 2012, Cedar Key's residents were told not to drink the tap water, until Hurricane Debbie recharged the aquifer.

“If there’s a threat to the region, it is changing freshwater flows that are going to change the estuaries,” he said.

Estuaries harbor a dense variety of plant and animal life in the brackish waters where fresh water drains into the salty seawater.

The Cedar Keys shelter estuaries between the islands and the mainland from the powerful forces of tides, winds and storms. They also protect towns, beaches and marshes from the full effects of the sea.

Still, these ever-changing islands are fragile.

"Keeping these islands in our future is something we have to be very vigilant about," Frederick said.

The simplest solution is to reduce our carbon footprint and burn fewer fossil fuels, as recent research has shown that curbing emissions can help prevent the seas from rising. But evidence from the past suggest seas could rise by at least 20 feet, if we change nothing.

While watching a scarlet sunset sink into the semi-glassy Gulf from its beach, or climbing the steel, spiral staircase to see a billion stars from the top of the lighthouse, it is easy to forget the threats facing Seahorse Key.

But that's the nature of barrier islands: They absorb the dangers.

On a boat dock at Seahorse Key, Captain Kenny McCain with UF’s Marine Lab told visiting students a story about the days when fishermen would hide their boats in the island’s cove during hurricanes.

“They’d say you’d hardly even know a storm was blowing,” McCain said.

Story by Stephenie Livingston, UF News

Nature photos by Jenny Adler, UF Ph.D. student and National Geographic Young Explorer, with additional images by Alisson Clark and Stephenie Livingston

Credits:

UF News

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