Dry Tortugas National Park


Dry Tortugas National Park is a national park of the United States located about west of Key West in the Gulf of Mexico, in the United States. The park preserves Fort Jefferson and the several Dry Tortugas islands, the westernmost and most isolated of the Florida Keys. The archipelago's coral reefs are the least disturbed of the Florida Keys reefs.
The park is noted for abundant sea life, tropical bird breeding grounds, colorful coral reefs, and shipwrecks and sunken treasures. The park's centerpiece is Fort Jefferson, a massive but unfinished coastal fortress. Fort Jefferson is the largest brick masonry structure in the Western Hemisphere, composed of more than 16 million bricks. Dry Tortugas is unique in its combination of a largely undisturbed tropical ecosystem with significant historic artifacts. The park is accessible only by seaplane or boat and has averaged about 63,000 visitors annually in the period from 2008 to 2017. Activities include snorkeling, picnicking, birdwatching, camping, scuba diving, saltwater fishing and kayaking. Overnight camping is limited to eight primitive campsites at the Garden Key campground, located just south of Fort Jefferson.
Dry Tortugas National Park is part of the Everglades & Dry Tortugas Biosphere Reserve, established by UNESCO in 1976 under its Man and the Biosphere Programme.

Geography

The Dry Tortugas is a small archipelago of coral islands about west of Key West, Florida. They represent the westernmost extent of the Florida Keys, though several reefs and submarine banks continue westward outside the park, beyond the Tortugas.
The park area is more than 99 percent water. The northern and western portions of the park, including the central island group, were designated a research natural area in 2007, in which no marine life may be taken, nor may vessels anchor. Vessels wishing to moor in this area must use designated mooring buoys or docks. About 54 percent of the park remains open for fishing. The park is bordered on the east, south and west by the Florida Keys National Marine Sanctuary, and on the northwest by the Tortugas Ecological Reserve.
The keys are low and irregular. Some have thin growths of mangroves, and various other vegetation, while the smallest have only small patches of grass, or no plant life. There are nominally seven islands, but there have been up to eleven during the past two centuries. The islands are continually changing in size and shape, and the number of distinct landmasses varies, as changing water levels expose and cover the lower islands and sandy land bridges between some of the islands. Some of the smaller islands have disappeared and reappeared multiple times as a result of hurricane impact. The major islands within the park are, roughly from west to east, Loggerhead Key, Garden Key, Bush Key, Long Key, Hospital Key, Middle Key, and East Key. The total land area within the park varies with water level. The total land area is about.
IslandAcres% of total
Total144.39100
Loggerhead Key64.2544.49
Garden Key4229.09
Bush Key29.6520.54
Long Key21.39
Hospital Key0.990.69
Middle Key1.51.04
East Key42.77

  • Loggerhead Key, in size, with an area of is the largest. This island has the highest elevation in the Dry Tortugas, at. The Dry Tortugas lighthouse, high, is on this island.
  • Garden Key, with Fort Jefferson and the inactive Garden Key lighthouse. It is east of Loggerhead Key. Garden Key is the second largest island in the chain, at in size, with an area of. The original size, before construction of Fort Jefferson, has been estimated at.
  • Bush Key, formerly named Hog Island because of the hogs that were raised there to provide fresh meat for the prisoners at Fort Jefferson, just a few meters east of Garden Key. At times, Bush Key is connected to Garden Key by a sand bar. The island is the third largest,, area, less than high. Bush Key is the site of a large tern rookery. It is closed to visitors from February to September to protect nesting sooty terns and brown noddies.
  • Long Key, south of the eastern end of Bush Key, in size, area of. At times it is connected to Bush Key by a sandbar.
  • Hospital Key, so called because a hospital for the inmates of Fort Jefferson had been built there in the 1870s. The island was formerly called Middle Key or Sand Key. It lies northeast of Garden Key and Bush Key,. Its area is, and it is above sea level at its highest point.
  • Middle Key, east of Hospital key,, area. Due to various seasonal changes, storm patterns and tidal cycles it is not always above sea level, disappearing for weeks or months, only to reappear again.
  • East Key, east of Middle Key,, area, over high.
The three westernmost keys, which are also the three largest keys, make up about 93 percent of the total land area of the group.

Former islands

Formerly existing keys were :
  • Southwest Key, disappeared by 1875, today a shoal south off of Loggerhead Reef.
  • Bird Key, was about southwest of Garden Key, disappeared in 1935. Current names in the area are Bird Key Bank and Bird Key Harbor. The Key was the site of numerous Union soldiers' graves during the Civil War.
  • North Key, probably identical with former Booby Island, current name in the area is North Key Harbor, an anchorage WSW of Pulaski Shoal, disappeared by 1875.
  • Northeast Key, was between East Key and North Key, slightly to the North, disappeared by 1875.

    Shoals with lights

  • Pulaski Shoal, marking the northeast edge of the group at, is not an island, but the former location of the Pulaski Shoal Light.
  • Iowa Rock, halfway between Garden Key and Hospital Key, is another site of a navigational light built in shallow water. It was destroyed by Hurricane Hugo, with three bare stumps left.

    Geology

The Dry Tortugas is the western extension of an arcuate chain of Pleistocene reef and oolitic limestone islands, with the eastern limit in the vicinity of Miami. These Florida Keys are the surface expression of the thick southern Florida carbonate platform, which has been accumulating sediments since the Early Cretaceous. Two stratigraphic units are exposed at the surface, the Key Largo Limestone and the Miami Limestone. The Key Largo Limestone are reefs up to 200 ft thick, parallel to the shelf edge, consisting of hermatypic corals and calcarenites. The Miami Limestone is less than 49 ft thick, and in general is found behind the Key Largo Limestone reef, but overlies it in the western extent of the keys. It consists of a bryozoan facies and an oolitic facies and represents a subtidal shoal. Additionally, excellent examples of Holocene carbonate-sand deposits are found in the Dry Tortugas, consisting mainly of disarticulated Halimeda plates. Between the Dry Tortugas and Key West is a 39 ft thick example of these sand deposits, known as "the quicksands".

Climate

Dry Tortugas has a tropical savanna climate, with a rainy season coinciding with the Atlantic hurricane season from May to October and a dry season extending from November through April. Despite occasional exposure to tropical systems, the Dry Tortugas is the driest place in Florida with an annual precipitation of about. There is no large jungle or forest canopy area on the islands, and the sandy soil and intense sun only enhance the drought-like conditions often found on the islands. Seasonally there is little temperature variation, with high temperatures in summer around and low temperatures in winter around. Like the rest of the lower keys, there has never been a recorded frost or freeze. The hardiness zone is 12a, with an annual mean minimum temperature of.

History

The first European to see the Dry Tortugas was Juan Ponce de León, who visited on June 21, 1513. Ponce de León caught 160 sea turtles there and subsequently referred to the islands as the "Tortugas". They are called Dry owing to the absence of surface fresh water on the island. The name is the second oldest surviving European place-name in the US.
The archipelago includes a high concentration of historically significant shipwrecks dating from the 17th century to the present. In 1742 wrecked in the Dry Tortugas. The stranded crew lived on Garden Key for 56 days, and fought a battle with a Spanish sloop, before sailing to Jamaica in several boats.
Florida was acquired from Spain by the United States in 1819. The Dry Tortugas were seen as a strategic point for the control of the Straits of Florida and the Gulf of Mexico. Work on a lighthouse on Garden Key started in 1825. In 1856 work on a new, more powerful lighthouse on Loggerhead Key was started to replace the Garden Key light.
John James Audubon visited the Tortugas in 1832 and so did Louis Agassiz in 1858.
The Dry Tortugas is also rich in maritime history. In 1989 Seahawk Deep Ocean Technology explored a shipwreck believed to be part of the 1622 Spanish treasure fleet. The wreck located in of water, yielded olive jars, copper, gold, silver, glass and other cultural artifacts. On September 6, 1622, the Nuestra Señora de Atocha was driven by a severe hurricane onto a coral reef near the Dry Tortugas, about west of Key West. Mel Fisher and his company discovered the wreck July 20, 1985. The estimated $450 million cache recovered, known as "The Atocha Motherlode", included 40 tons of gold and silver; there were some 114,000 of the Spanish silver coins known as pieces of eight, gold coins, Colombian emeralds, gold and silver artifacts, and 1,000 silver ingots. In addition to the Atocha, Fisher's company, Salvors Inc., found remains of several nearby shipwrecks, including the Atocha's sister galleon the Santa Margarita, lost in the same year, and the remains of a slave ship known as the Henrietta Marie, lost in 1700.