Dry Tortugas National Park

Park Information

• Date Established: January 4, 1935 (Fort Jefferson National Monument); October 26, 1992 (Dry Tortugas National Park)
• Location: Key West, Florida
• Area: 100 square miles (259 square kilometers)

Overview

Dry Tortugas National Park is located off the coast of Key West, Florida. The islands rim the main shipping channel between the Atlantic Ocean, Gulf of Mexico, and the western Caribbean Sea. Spanish explorers and merchants often stopped on the islands while using the shipping channel and voyaging along the Gulf Coast. The islands are low and flat; over the centuries, hundreds of ships have met their doom in the hazardous coral reefs.

The Dry Tortugas comprise seven keys in the Gulf of Mexico: Bush, East, Garden, Hospital, Loggerhead, Long, and Middle. More than 99 percent of the park is water. The park was established to protect the islands and marine ecosystems, and to preserve the structures and many shipwrecks in the area.

A major attraction is historic Fort Jefferson. This former military structure was also a prison and housed, among others, four men who were convicted of conspiring to assassinate President Abraham Lincoln. Five of the islands are nature reserves. Many visitors to the park are drawn to the bird populations. Snorkelers explore the coral reefs, with abundant tropical fish, and scuba divers explore shipwreck sites. Other activities include kayaking, fishing, and camping.

History

Ponce de Leon discovered the islands in 1513 and named them Las Tortugas for the giant sea turtles he found in the waters. Sailors later called the islands the Dry Tortugas because they did not have freshwater.

A lighthouse was built on Garden Key in 1825 to warn ships to avoid the reefs, and a brick tower lighthouse was constructed in 1858 on Loggerhead Key. Garden Key, the main island, is the site of Fort Jefferson, the largest all-masonry fort in the United States. This hexagonal structure, which features two thousand arches, was envisioned as a military fortification to protect commerce in the shipping channel. It was used as a prison late in the nineteenth century. The fort is encircled by a wall that was begun before the American Civil War (1861–1865). The first bricks, which form the base of the wall, were purchased around 1845 from a place near Pensacola, Florida. These pink and brown bricks were used when construction began in 1846. With the outbreak of war, Southern merchants refused to honor their contracts. Builders turned to New England brick makers, who provided the remainder of the materials—the traditional dark red bricks of which the top section is made. Construction ended in 1875, although the fort was incomplete, because of concerns that further building would increase already troubling subsidence problems.

When President Franklin D. Roosevelt signed the Antiquities Act on January 4, 1935, he designated Fort Jefferson National Monument. It was at that time 47,125 acres, but was expanded in 1983. An act of Congress designated it Dry Tortugas National Park on October 26, 1992.

The islands are primarily composed of sand, so they are constantly changing as the currents and winds act upon them. Hurricanes sometimes drastically alter the size and shape of the islands. Sediment primarily drifts westward, and as a result, Bush Key has slowly been moving closer to Garden Key. In some cases, land bridges between islands appear and disappear frequently. Five of the islands are off-limits to humans and show no evidence of human habitation. Modern visitors travel to the remote park by ferry, seaplane, or boat.

Live coral reefs in the park have been growing for more than eleven thousand years, but since the 1980s their health has been declining because of bleaching and disease. The park has established a number of coral reef rehabilitation programs and wildlife protection areas.

Because of its location, Dry Tortugas National Park is sometimes in the path of dangerous weather. In 2022, the islands were directly struck by Hurricane Ian. Two years later, the park was once again struck by Hurricane Helene. Both hurricanes resulted in temporary closures of parts of the park for damage assessment and repair.

Geology and Ecology

Florida, including the keys, is located on a platform known as the Florida plateau. It was formed by marine sedimentation and volcanic activity about 530 million years ago, and was part of Pangaea, the supercontinent. Pangaea gradually split because of the movement of the tectonic plates of the crust. Florida was between the masses that eventually drifted apart to become the Americas and Africa. About two million years ago, much more of the land was exposed because sea levels were much lower. The land was much drier as well. About ten thousand years ago, near the end of the last ice age, Paleoindians settled in Florida. As the ice age ended, sea levels rose and the climate became wetter.

Much of the Florida plateau is composed of sedimentary rock, from deposits during periods of high sea levels. The portions of the platform below water level were constantly eroded by waves and currents, but coral reefs established themselves in many areas of the submerged platform. As sea creatures and algae died and sank to the bottom, the calcium carbonate formed sedimentary limestone bedrock. The southwestern Florida Keys were formed when the ocean levels dropped and exposed coral reefs and sandbars. The sandbars eventually fossilized, forming the rocks of the islands. This limestone, formed during the Pleistocene Epoch, is the bedrock of all the Florida Keys.

Loggerhead Key is the only island in Dry Tortugas National Park that has outcrops of beach rock. This sedimentary rock along the shoreline formed beneath a thin layer of unconsolidated sediments in the area between high and low tides. This develops because evaporation causes seawater to become highly concentrated with calcium carbonate, which acts as a glue to bind some sediments, such as shells and coral. Beachrock is often fractured, with breaks called joints that point toward the sea.

The seabed in the park varies. Coral reefs include more than fifty species, primarily brain and star corals, as well as threatened species, such as elkhorn and staghorn. Some areas of the park contain seagrass beds, which are important habitats for marine life such as small organisms and juvenile reef fish. Seagrass beds trap sediment and protect the coral from erosion, which is a concern because the region is prone to hurricanes. Other areas of the seabed are sediments, which include particles of Key Largo Limestone as well as gravel, sand, silt, and fine-grained mud. Some small areas of unconsolidated sediment thinly cover the rock substrate, known as hardbottom or pavement. In the park, the pavement is limited to sedimentary stone.

The wildlife is varied. Endangered sea turtles nest on some beaches between May and October, and as a result, these beaches are often closed at times to protect the hatchlings. The islands frequently host birds migrating between North and South America. Year-round residents include brown pelicans, double-crested cormorants, frigate birds, and sandpipers.

Bibliography

Allen, Ginger M., and Martin B. Main. “Florida’s Geological History.” University of Florida Institute of Food and Agricultural Sciences, Aug. 2014, edis.ifas.ufl.edu/uw208. Accessed 8 Dec. 2024.

“Explore a 19th Century Fort and Snorkel Crystal Clear Water with Incredible Marine Life.” National Park Service, 20 June 2021, www.nps.gov/drto/index.htm. Accessed 8 Dec. 2024.

“Geology.” National Park Service, 29 July 2015, www.nps.gov/drto/learn/nature/geology.htm. Accessed 8 Dec. 2024.

“History & Culture.” National Park Service, 11 Jan. 2018, www.nps.gov/drto/learn/historyculture/index.htm. Accessed 8 Dec. 2024.

“Nature & Science.” National Park Service, 28 Sept. 2018, www.nps.gov/drto/learn/nature/index.htm. Accessed 8 Dec. 2024.

"South Florida National Parks Report Status After Hurricane Helene." National Park Service, 28 Sept. 2024, www.nps.gov/drto/learn/news/post-hurricane-helene-status.htm. Accessed 8 Dec. 2024.

Van Buren, Alex. “A Guide to Dry Tortugas National Park.” Travel + Leisure, 20 Feb. 2023, www.travelandleisure.com/trip-ideas/national-parks/dry-tortugas-national-park-guide. Accessed 8 Dec. 2024.