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Perdido Key is a barrier island on the north coast of the Gulf of Mexico. The island extends from Pensacola Pass on the east to Perdido Pass on the west. Most of the island is in Florida, with the western end of the island in Alabama. Santa Rosa Island is to the east of the island, and Alabama Point is to the west. Perdido Key was attached to the mainland until the 1940s when a canal separated it from the mainland. The eastern part of the island forms part of the Gulf Islands National Seashore, which includes the Perdido Key Historic District, the site of three shore batteries that once defended Pensacola Bay. The rest of the island, with the exception of the Perdido Key State Park, has been developed as a resort and residential community. As a barrier island, Perdidio Key is subject to changes due to wave action and longshore currents, particularly from hurricanes. The endangered Perdido Key beach mouse is Endemism to the island.
Perdido Key is connected to the Florida mainland via the Theo Baars Bridge across the Intracoastal Waterway on Florida State Road 292 and to the Alabama mainland via the Perdido Pass Bridge on Alabama State Route 182. Ono Island is connected to the Alabama portion of Perdido Key by a private bridge.
Perdido Pass, the western end of Perdido Key, was about east of its present location until early in the 20th century. The barrier spit on the western (Alabama) side of the inlet, Point Ornocor, overlapped what is now Perdido Key, extending for several miles parallel to and on the north side of Perdido Key. As a result, the water passage from Perdido Pass to Perdido Bay was long, narrow and winding, passing between Perdido Key and Point Orconor, doubling the end of the point and then passing back between the point and the Florida shore on the north side. In early 1906, local residents dug a new inlet through Point Ornocor about west of the old inlet. The new inlet was widened by the 1906 Mississippi hurricane. The old inlet then silted up and closed, with the result that the portion of Point Ornocor east of the new inlet was attached to Perdido Key and the Florida mainland. The original waterway from the old Perdido Pass to Perdido Bay became known as Old River. A passage later opened from the western end of Old River to the Bayou St. John near the new Perdido Pass, separating what is now Ono Island from Perdido Key. The spit ending on the west side of Perdido Pass is now known as Alabama Point. Alabama and Florida settled the location of the state line in 1953, placing it at the location of the old Perdido Pass. In the early 1940s the Gulf Intracoastal Waterway was constructed between Perdido Key and the mainland, including the dredging of a canal through the neck of the peninsula connecting Perdido Key to the mainland, thus turning Perdido Key into an island.
Perdido Key is shifting westward due to longshore drift. Both Pensacola Pass and Perdido Pass have historically moved westward. The westward flowing longshore current accretes sand on the up-current (eastern) sides of the passes and erodes sand from the down-current (western) sides. The site of the original Fort McRee, built in 1830 on the eastern end of Perdido Key (then known as Foster's Bank), was in the channel in the middle of Pensacola Pass by 1979. Pensacola Pass has been dredged since 1883 to maintain a channel into Pensacola Bay for United States Navy and other ships. The dredging has interrupted the natural transport of sand across the inlet from Santa Rosa Island to Perdido Key, with the result that Pensacola Pass is a net sediment sink. This has starved the eastern end of Perdido Key of sand, leading to the erosion of that part of the island.
Much of the sand that makes up Perdido Key comes from the Gulf of Mexico floor offshore of the island. About of sand is deposited on the island from offshore each year. Part of that sand is carried west by longshore currents. Another part of the sand is carried, at infrequent intervals, across the island to and beyond the north side of the islands by Overwash during hurricanes. With the reduction of sand crossing Pensacola Pass due to dredging of the inlet, most of the eastern half of the island is eroding, while the western half of the islands is accreting sand. The easternmost part of the island is receiving sand dredged from the inlet in a beach nourishment project. In the period from 1920 until 2013, the easternmost of the island lost an average of of shoreline per year.
Perdido Key has been severely damaged by several hurricanes since the 1970s; Frederic in 1979, Erin in August 1995, Hurricane Opal in October 1995, Hurricane Ivan in 2004, Hurricane Dennis in 2005, and Hurricane Sally in 2020 damaged or destroyed foredunes and eroded beaches, causing the shoreline to retreat northward as much as in each storm. Ivan brought a storm surge to the island, damaging secondary dunes as well as washing away foredunes, and causing washovers. Sally breached the eastern end of the island in three places, creating new inlets, all of which closed again within eight months. Vegetation on Perdido Key can take many years to recover from damage caused by hurricane winds.
In 1898, construction was started on two coastal artillery installations, Battery Center and Battery Slemmer, at Fort McRee, to the west of the ruins of the mid-19th century fort on Foster's Bank (Perdido Key). The batteries were part of defenses for Pensacola Bay, which also included batteries at Fort Barrancas and Fort Pickens. The batteries were completed in 1900. Battery Slemmer was deactivated in 1918. Battery Center's guns were removed in 1920. Construction of new defenses for Pensacola Bay started in 1940. Battery 233 was built behind the ruins of Battery Slemmer on Perdido Key. Battery 233 had not yet received its intended guns when World War II ended in 1945 and Fort McRee, including the battery, was deactivated. The ruins of batteries Center, Slemmer, and 233 are preserved in the Perdido Key Historic District.
A long-term survey of the Perdido Key unit of the Gulf Islands National Seashore identified 384 plant species. Four plant species on the island are of concern for conservation. Chrysopsis godfreyi (Godfrey's goldenaster) is rated "imperiled" on the NatureServe conservation status scale. Schizachyrium maritimum (gulf bluestem) and Polygonum smallianum (largeleaf jointweed) are rated "vulnerable" on the NatureServe conservation status scale. Crocanthemum arenicola (syn. Helianthemum arenicola) (gulf coast frostweed) has a limited distribution, occurring only along the north coast of the Gulf of Mexico, from Franklin County, Florida to Harrison County, Mississippi.
Animals found on Perdido Key include the endangered Perdido Key beach mouse and two nesting shorebirds, Charadrius nivosus (snow plover) and Sternula antillarum (least tern). Loggerhead sea turtles ( Caretta caretta) occasionally lay eggs in nests on the island. Ridley sea turtles ( Lepidochyles spp.) have left nests on the island on rare occasions. Various shorebirds and migrating birds use the island for resting and foraging.
Parks
The Perdido Key unit of the Gulf Islands National Seashore started with the Fort McRee site at the extreme eastern end of the island, which was transferred from the US Department of Defense to the National Park Service in 1971. Rosamond Johnson Beach, just to the east of the middle of the island, was added to the national seashore in 1973. In 1977–1978, of the island between Rosamond Johnson Beach and Fort McRee were acquired and added to the Rosamund Johnson Beach Area of the national seashore.
Ecology
Perdido Key has deep, sandy soils. In the undeveloped parts of the island, swales between dunes host a patchwork of mesic , coastal Shrubland, and coastal . Those habitats may be flooded by storm surges, after which they are colonized by Halophyte. Swampy areas north of the dunes are drained by creeks. Salt marshes occur along the north side of the island.
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