The sun is setting over the coastal marshes where mainland Georgia dissolves into muck, spartina grass and saltwater, then re-forms as barrier islands. The tide is out, and below the Jekyll Island Club Wharf the water has receded, exposing mud and tiny oxbow rivers rushing around clumps of grass.

A shrimp boat motors past, bulging nets hanging from its arms. Birds swarm around it, circling the masts in a halo of black.

Georgia’s barrier islands are nothing like those we’re accustomed to in South Florida. They are low-key, devoid of high-rises and freeways. Separated from the mainland by ecologically rich marshlands, the islands are — officially or unofficially — wildlife refuges, supporting sea turtles, roseate spoonbills, marsh wrens, oysters and hundreds of other species. The sea is simultaneously friend and foe, depositing sand to form delicate dunes in one spot while viciously eating away the land elsewhere on the same island.

Each island is unique and memorable. A century or more ago, wealthy industrialists built lavish mansions, summer “cottages” and hunting lodges on some islands. Others supported plantations where slaves worked crops of sea cotton, indigo or rice. The Georgia coast was a buffer between English settlers to the north and Spanish colonists in Florida, with many landings protected by forts.

Today a fleet based in Brunswick works the waters around these islands, netting shrimp and other seafood. Some of the Gilded Age mansions are rotting away; others have been refurbished and are run as inns. Sapelo Island has a Gullah community, founded by former slaves. Jekyll Island has a rehabilitation center for injured sea turtles. There are luxury resorts, marine research stations, protected Indian shell mounds, wild horses, fishing piers that double as social venues and old forts that have been turned into parks.

Some of the islands along Georgia’s 150-mile coastline are wildlife sanctuaries or research stations not open to the public; others are private. This tale isn’t a comprehensive report but a story about seven islands, south to north, visited over 18 months.

CUMBERLAND ISLAND

It is New Year’s Day, cold and wet, and the people getting on the ferry ahead of me are going camping. They are carrying suitcases, camping gear, at least 20 bundles of firewood, cases of bottled water and big trash bags stuffed with drinks, groceries and other goods. There is no food or anything else for sale on the island, so they bring everything they could possibly need.

Unlike the campers, my sister and I are on a day trip. We’ve packed only sandwiches and sweatshirts in a backpack and will be returning to St. Marys on the mainland this afternoon.

Cumberland Island, the 19th century retreat of a branch of the Carnegie family, is a national seashore managed by the National Park Service, just across the Florida state line. The only places to spend the night are the inn and the campground. There are no stores. Miss the return ferry, we’re warned several times, and we’ll spend the night in the open with no gear or food.

With a little over four hours to spend, we limit ourselves to the southern end of the 17-mile-long island. We’ll have to skip the tiny First African Baptist church where John Kennedy Jr. and Carolyn Bessettte were married in 1996, the Plum Orchard Georgian Revival mansion built by the Carnegie family, the isolated and elegant Greyfield Inn where rooms start at $395 a night, meals included. But that will leave us time for a guided tour by a park ranger that includes the ruins of the Carnegies’ Dungeness mansion, a quick hike on our own to the beach on the eastern shore where we spot a few of the island’s famous wild horses and a brisk walk to the next ferry landing, about a mile north of where we first came ashore.